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TRANSPORTATION ENGINEERING I
Department of Civil Enginnering
(B.Tech 4
th semester)
Faculty Name : M.Ankita
CONTENTS
PART – A
UNIT – 1
PRINCIPLES OF TRANSPORTATION ENGINEERING:
Importance of transportation, Different modes of transportation and comparison,
Characteristics of road transport Jayakar committee recommendations, and
implementation – Central Road Fund, Indian Roads Congress, Central Road Research
Institute
04 Hrs
UNIT – 2
HIGHWAY DEVELOPMENT AND PLANNING:
Road types and classification, road patterns, planning surveys, master plan – saturation
system of road planning, phasing road development in India, problems on best
alignment among alternate proposals Salient Features of 3rd and 4th twenty year road
development plans and Policies, Present scenario of road development in India (NHDP
& PMGSY) and in Karnataka (KSHIP & KRDCL) Road development plan - vision
2021.
06 Hrs
UNIT – 3
HIGHWAY ALIGNMENT AND SURVEYS:
Ideal Alignment, Factors affecting the alignment, Engineering surveys-Map study,
Reconnaissance, Preliminary and Final location & detailed survey, Reports and
drawings for new and re-aligned projects
04 Hrs
HIGHWAY GEOMETRIC DESIGN – I:
Importance, Terrain classification, Design speed, Factors affecting geometric design,
Cross sectional elements-Camber- width of pavement- Shoulders-, Width of
formation- Right of way, Typical cross-sections
05 Hrs
UNIT – 4
HIGHWAY GEOMETRIC DESIGN – II:
Sight Distance- Restrictions to sight distance- Stopping sight distance- Overtaking sight
distance- overtaking zones- Examples on SSD and OSD- Sight distance at intersections,
Horizontal alignment-Radius of Curve- Super elevation – Extra widening- Transition
curve and its length, setback distance – Examples, Vertical alignment-Gradient-summit
and valley curves with examples.
07 Hrs
UNIT – 5
PAVEMENT MATERIALS:
Subgrade soil – desirable properties-HRB soil classification-determination of CBR and
modulus of subgrade reaction-Examples on CBR and Modulus of subgrade reaction,
Aggregates- Desirable properties and list of tests, Bituminous materials-Explanation on
Tar, bitumen, cutback and emulsion-List of tests on bituminous materials.
06 Hrs
UNIT – 6
PAVEMENT DESIGN:
Pavement types, component parts of flexible and rigid pavements and their functions,
design factors, ESWL and its determination-Examples, Flexible pavement- Design of
flexible pavements as per IRC;37-2001-Examples, Rigid pavement- Westergaard‟s equations for load and temperature stresses- Examples- Design of slab thickness only as
per IRC:58-2002
06 Hrs
UNIT – 7
PAVEMENT CONSTRUCTION:
Earthwork –cutting-Filling, Preparation of subgrade, Specification and construction of
i) Granular Sub base, ii) WBM Base, iii) WMM base, iv) Bituminous Macadam, v)
Dense Bituminous Macadam vi) Bituminous Concrete, vii) Dry Lean Concrete sub base
and PQC viii) concrete roads
05 Hrs
HIGHWAY DRAINAGE:
Significance and requirements, Surface drainage system and design-
Examples, sub surface drainage system, design of filter materials
03 Hrs UNIT – 8
HIGHWAY ECONOMICS:
Highway user benefits, VOC using charts only-Examples, Economic analysis - annual
cost method-Benefit Cost Ratio method-NPV-IRR methods- Examples, Highway
financing-BOT-BOOT concepts
06 Hrs
4
TEXT BOOKS:
1. Highway Engineering – S K Khanna and C E G Justo, Nem Chand Bros, Roorkee 2. Highway Engineering - L R Kadiyali, Khanna Publishers, New Delhi
3. Transportation Engineering – K P Subramanium, Scitech Publications, Chennai 4. Transportation Engineering – James H Banks, Mc. Graw. Hill Pub. New Delhi
5. Highway Engineeering –R. Sreenivasa Kumar, University Press. Pvt.Ltd. Hyderabad
REFERENCE BOOKS:
1. Relevant IRC Codes
2. Specifications for Roads and Bridges-MoRT&H, IRC, New Delhi. 3. Transportation Engineering – C. Jotin Khisty, B. Kent lal, PHI Learning Pvt Ltd,
New Delhi.
LIST OF CONTENTS
UNIT-1 PRINCIPLES OF TRANSPORTATION ENGINEERING 1
Introduction 09
Importance of Transportation 10
Different Modes of Transportation 12
Characteristics and Comparison of Different Modes 14
Jayakar Committee Recommendations and Implementation 16
Central Research Fund (CRF) 17
Indian Road Congress (IRC) 17
Central Road Research Institute (CRRI) 18
UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING
Introduction 19
Classification of roads 21
Road patterns 22
Planning Surveys 23
Master plan 25
Saturation System 26
Road development Plan 27
UNIT-3 HIGHWAY ALIGNMENT
Alignment 30
Requirements 30
Factors Controlling Alignment 31
UNIT-4 HIGHWAY GEOMETRIC DESIGN 1 & 2
Introduction 33
6
Factors affecting geometric design 33
Camber 35
Width of carriageway 36
Kerbs 36
Road margins 37
Shoulders 37
Parking Lanes 37
Bus- Bays 37
Service roads 38
Footpath 38
Guard Rails 38
Width of Formation 38
Right of way 39
Sight Distance 40
Types of Sight Distance 40
Stopping sight distance 42
Overtaking sight distance 43
Overtaking zones 45
Horizontal curves 46
Analysis of super-elevation 48
Horizontal Transition curves 52
Length of Transition curves 53
Setback Distance 54
Vertical alignment 57
Gradient 58
Summit Curve
Valley curve 61
UNIT-5 PAVEMENT MATERIALS
Introduction 65
Subgrade Soil 65
Desirable Properties 65
Soil Classification 66
Highway research board (HRB) classification of soils 66
California bearing ratio (CBR) test 67
AGGREGATES 73
Tests on Road aggregate 74
BITUMINOUS MATERIALS 75
Types of bituminous materials 75
Tests on Bitumen 76
Bituminous Emulsion 78
BITUMINOUS PAVING MIXES 81
UNIT-6 INTRODUCTION TO PAVEMENT DESIGN
Requirements of a pavement 82
Types of pavements 82
Flexible Pavements 82
Rigid Pavements 83
Types of Rigid pavements 84
Factors affecting Pavement design 85
IRC method of Design of Flexible Pavements 89
Rigid pavement Design 92
8
Wheel load Stresses- Westergaard‟s equation 92
UNIT-7 HIGHWAY CONSTRUCTION
Introduction 95
Earthwork 95
Construction of Earth Roads 99
Construction of Gravel Roads 100
Construction of WBM Roads 101
Construction of Bituminous Pavements 105
Construction procedure for Bituminous Concrete 110
HIGHWAY DRAINAGE 117
Introduction 117
Importance of Highway Drainage 117
UNIT-8 HIGHWAY ECONOMICS & FINANCE
Introduction 122
Highway User benefits 122
Annual Highway Cost 136
HIGHWAY FINANCE 128
Highway financing in India 128
9
UNIT-I PRINCIPLES OF TRANSPORTATION
ENGINEERING-I
INTRODUCTION
Basic Definition: A facility consisting of the means and equipment necessary for the
movement of passengers or goods. At its most basic, the term “transportation system”
is used to refer to the equipment and logistics of transporting passengers and goods. It
covers movement by all forms of transport, from cars and buses to boats, aircraft and
even space travel. Transportation systems are employed in troop movement logistics
and planning, as well as in running the local school bus service.
Function: The purpose of a transportation system is to coordinate the movement of
people, goods and vehicles in order to utilize routes most efficiently. When
implemented, transportation systems seek to reduce transport costs and improve
delivery times through effective timetabling and route management. Periodic re-
evaluations and the development of alternative routes allow for timely changes to the
transportation system in order to maintain efficiency.
Features: A standard transportation system will usually feature multiple timetables
designed to inform the user of where each vehicle in the fleet is expected to be at any
given point in time. These timetables are developed alongside an array of route plans
designed to coordinate vehicle movements in a way that prevents bottlenecks in any
one location.
Benefits: The main benefit of implementing a transportation system is delivery of
goods and personnel to their destinations in a timely manner. This in turn increases the
efficiency of vehicle use, as the same vehicle can be used for “multi-drop” jobs, such
as bus services or home delivery networks, far more effectively when their routes are
planned in advance rather than being generated “on the fly.”
Size: Transportation systems are developed in a wide variety of sizes. Local transport
networks spanning the bus network for a city and its suburbs are common, as are
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country-wide delivery networks for haulage firms. Airlines use international
transportation systems to coordinate their flights. The larger the distance being covered,
the more effective the use of vehicles when a transportation system is used.
IMPORTANCE OF TRANSPORTATION
The world that we live in now will most likely be impossible had it not been for
innovations in transportation. There would not have been any great infrastructure,
industrialization, or massive production, if transportation was incompetent. Life would
not have kept up with the fast changing times if there were no huge trucks, bulldozers,
trailers, cargo ships, or large aircrafts to carry them to different places. In other words,
the global society would not have experienced comfort and convenience had it not been
for advancements in the transportation sector. Today, humanity has technology to thank
for all the wonderful things that it currently enjoys now.
Transportation is vital for the economic development of any region since every
commodity produced whether it is food, clothing, industrial products or medicine needs
transport at all stages from production to distribution. In the production stage
transportation is required for carrying raw materials like seeds, manure, coal, steel etc.
In the distribution stage transportation is required from the production centre‟s viz;
farms and factories to the marketing centres and later to the retailers and the consumers
for distribution.
The transportation has lots of advantages and even disadvantages. The more
focus is on advantages as we cannot think about the life without transportation. The
importance of transportation may include:
Availability of raw materials: Transportation helps in carrying the raw
materials from one place to another place. Initially raw materials are made at one
place and are being transported to another place for processing and for
manufacturing goods.
Availability of goods to the customer: The goods are being transported from
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one place to another place. These goods which are produced at one place are
transported
to other distant places for their usage. It flexibly moves the goods from one
place to another place.
Enhances the Standard Of Living: It improves the standard of living. As the
transportation of each and every good is being done then the productivity
increases which results in the reduced or the effective costs. Because of
reduction in the cost they can use different commodities for different purposes
and can lead a secure life.
Helps a lot during the emergencies and even during natural disasters:
Transportation helps during the natural disturbances. It helps in quick moving
from one place to another place and supplies the required operations.
Helps for the employment: Transportation provides employment for many
people as drivers, captains, conductors, cabin crew and even the people are used
for the construction of different types of transportation vehicles. And even by the
use of transportation the remote people are being employed with the access to
the urban facilities and the opportunities.
Helps in mobility of the laborers: Many people are traveling to other countries
on their employment basis. Transportation plays an important role in such cases.
Helps for bringing nations together: Transportation on the whole is used for
globalization i.e. it brings nations together and it creates awareness about the
cultural activities and even about the industries and helps a lot for importing and
exporting of different goods.
These above are some of the necessities which make us to use transportation.
The importance and adequacy of transportation system of a country indicates its
economic and social development.
Economic Activity: Two important factors well known in economic activity are:
Production or supply and
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Consumption for human wants or demand.
Social Effects: The various social effects of transportation may be further classified into: Sectionalism and transportation
Concentration of population into urban
area Aspect of safety, law and order.
DIFFERENT MODES OF TRANSPORTATION
Three basic modes of transport are by land, water and air. Land has given
development of road and rail transport. Water and air have developed waterways and
airways respectively. Apart from these major modes of transportation, other modes
include pipelines, elevators, belt conveyors, cable cars, aerial ropeways and monorails.
Pipe lines are used for the transportation of water, other fluids and even solid particles
The four major modes of transportation are:
Roadways or highways
Railways
Airways
Waterways.
Airways:
The transportation by air is the fastest among the four modes.
Air also provides more comfort apart from saving in transportation time for the
passengers and the goods between the airports.
Waterways:
Transportation by water is the slowest among the four modes.
This mode needs minimum energy to haul load through unit distance The transportation by water is possible between the ports on the sea routes or along
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the rivers or canals where inland transportation facilities are available.
Railways:
The transportation along the railway track could be advantageous by railways
between the stations both for the passengers and goods, particularly for longer
distances.
The energy requirement to haul unit load through unit distance by the railway is
only a fraction (one fourth to one sixth) of the required by road.
Hence, full advantage of this mode of transportation should be taken for the
transportation of bulk goods along land where the railway facilities are
available.
Roadways:
The transportation by road is the only mode which could give maximum service
to one and all.
The road or highways not only include the modern highway system but also the
city streets, feeder roads and village roads, catering for a wide-range of road
vehicles and the pedestrians.
This mode has also maximum flexibility for travel with reference to route,
direction, time and speed of travel etc. through any mode of road vehicle.
It is possible to provide door to door service by road transport.
The other three modes (railways; water ways; airways) has to depend on the
roadway for the service.
Ultimately, road network is therefore needed not only to serve as feeder system
for other modes of transportation and to supplement them, but also to provide
independent facility for road travel by a well planned network of roads
throughout
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CHARACTERISTICS AND COMPARISON OF DIFFERENT MODES
It is accepted that the fact road transport is the nearest to the people. The
passengers and goods have to be first transported by road before reaching a railway
station or an airport. It is seen that road network alone could serve the remotest villages
of the vast country like occurs.
The various characteristics (advantages) and disadvantages of different mode of
transport are briefly listed here:
Roadways:
Advantages:
Flexibility: It offers complete freedom to the road users.
It requires relatively smaller investments and cheaper in construction with respect to
other modes.
It serves the whole community alike the other modes.
For short distance travel it saves time.
These are used by various types of vehicles.
Disadvantages:
Speed is related to accidents and more accidents results due to higher speed.
Not suitable for long distance travel
Power required per tonne is more.
Railways:
Advantages:
Can transport heavy loads of goods at higher speed
Power required per tonne is less compared to roadways
Chances of accidents are less.
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Disadvantages:
Entry and exist points are fixed
Requires controlling system and no freedom of movement
Establishment and maintenance cost is higher.
Waterways:
Advantages:
Cheapest: Cost per tonne is lowest
Possess highest load carrying capacity
Leads to the development of the industries.
Disadvantages:
Slow in operation and consumes more time
Depends on weather condition
Chances of attack by other countries on naval ships are more.
Ocean tides affect the loading and unloading operation
The route is circuitous.
Airways:
Advantages:
It has highest speed
Intercontinental travel is possible
Journey is continuous over land and water
Disadvantages:
Highest operating cost (cost/tonne is more)
Load carrying capacity is lowest
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Depends on weather condition
Should follow the flight rules.
JAYAKAR COMMITTEE RECOMMENDATIONS AND IMPLEMENTATION
RECOMMENDATIONS: Over a period after the First World War, motor vehicles
using the roads increased and this demanded a better road network which can carry
mixed traffic conditions. The existing roads when not capable to withstand the mixed
traffic conditions. For the improvement of roads in India government of India appointed
Mr. Jayakar Committee to study the situations and to recommend suitable measures for
road improvement in 1927 and a report was submitted in 1928 with following
recommendations:
Road development in the country should be considered as a national interest. As
the provincial and local government do not have the financial and technical
capacity for road development.
Extra tax to be levied from the road users as fund to develop road.
A Semi-official technical body has to be formed to collect and pool technical
knowhow from various parts of the country and to act as an advisory body on
various aspects of the roads.
A research organization should be instituted at National level to carry out research and
development work and should be available for consultation. IMPLEMENTATIONS:
Majority of the recommendations were accepted by the government
implemented by Jayakar Committee.
Some of the technical bodies were formed such as,
• Central Road Fund (CRF) in 1929
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• Indian Road Congress (IRC) in 1934
• Central Road Research Institute (CRRI) in 1950.
Central Research Fund (CRF):
Central Research Fund (CRF) was formed on 1st
March 1929
The consumers of petrol were charged an extra levy of 2.64 paisa/litre of petrol
to buildup this road development fund.
From the fund collected 20 percent of the annual revenue is to be retained as
meeting expenses on the administration of the road fund, road experiments and
research on road and bridge projects of special importance.
The balance 80 percent of the fund to be allotted by the Central Government to
the various states based on actual petrol consumption or revenue collected
The accounts of the CRF are maintained by the Accountant General of Central
Revenues.
The control of the expenditure is exercised by the Roads Wings of Ministry of
Transport.
Indian Road Congress (IRC):
It s a semi -official technical body formed in 1934.
It was formed to recommend standard specifications.
It was constituted to provide a forum of regular technical pooling of experience
and ideas on all matters affecting the planning, construction and maintenance of roads
in India.
IRC has played an important role in the formulation of the 20-year road
development plans in India.
Now, it has become an active body of national importance controlling
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specifications, guidelines and other special publications on various aspect of Highway
Engineering.
Central Road Research Institute (CRRI):
CRRI was formed in the year 1950 at New Delhi
It was formed for research in various aspect of highway engineering
It is one of the National laboratories of the Council of Scientific and Industrial
Research.
This institute is mainly engaged in applied research and offers technical advice to
state governments and the industry on various problems concerning roads.
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UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING
INTRODUCTION `
Highway design is only one element in the overall highway development
process. Historically, detailed design occurs in the middle of the process, linking the
preceding phases of planning and project development with the subsequent phases of
right-of-way acquisition, construction, and maintenance. While these are distinct
activities, there is considerable overlap in terms of coordination among the various
disciplines that work together, including designers, throughout the process.
It is during the first three stages, planning, project development, and design, that
designers and communities, working together, can have the greatest impact on the final
design features of the project. In fact, the flexibility available for highway design during
the detailed design phase is limited a great deal by the decisions made at the earlier
stages of planning and project development. This Guide begins with a description of the
overall highway planning and development process to illustrate when these decisions are
made and how they affect the ultimate design of a facility
Meaning of Highway and Road:
Road: A road is a thoroughfare, route or way on land between two places, which
typically has been paved or otherwise improved to allow travel by some conveyance,
including a horse, cart, or motor vehicle.
Highway: A highway is a public road, especially a major road connecting two or more
destinations. Any interconnected set of highways can be variously referred to as a
"highway system", a "highway network", or a "highway transportation system". Each
country has its own national highway system.
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TYPES OF ROAD:
Basically, different types of roads can be classified into two categories namely,
All-weather roads
and
Fair-weather roads.
All-weather roads: These roads are negotiable during all weather, except at major
rivercrossings where interruption of traffic is permissible upto a certain limit extent, the
road pavement should be negotiable during all weathers.
Fair-weather roads: On these roads the traffic may be interrupted during monsoon
season atcauseways where streams may overflow across the roads.
CLASSIFICATION OF ROADS:
Roads are classified based on various aspects namely,
1) Based on the carriage way,
Paved Roads: These roads are provided with a hard pavement course which
should be atleast a water bound macadam (WBM) layer.
Unpaved Roads: These roads are not provided with a hard pavement course of
atleast a WBM layer. Thus earth roads and gravel roads may be called as
unpaved roads.
2) Based on Surface pavement provided,
Surface Roads: These roads are provided with a bituminous or cement concrete
surfacing.
Unsurfaced Roads: These are not provided with bituminous or cement concrete
surfacing.
Roads which are provided with bituminous surfacing are called as black toped
roads and that of concrete are referred to as concrete roads respectively.
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3) Based on Traffic Volume:
Heavy
Medim
Light traffic roads.
4) Based on Load transported or
tonnage: Class-I or Class-A Class-II orClassB.
5) Based on location and Function:
National Highways (NH): The NH connects the capital cities of the states and
the capital cities to the port. The roads connecting the neighbouring countries
are also called as NH. The NH are atleast 2 lanes of traffic about 7.5m d wide.
The NH are having concrete or bituminous surfacing.
State Highways (SH): SH are the main roads within the state and connect
important towns and cities of state. The width of state highways is generally
7.5m.
Major District Roads (MDR): These roads connect the areas of production and
markets with either a SH or railway. The MDR should have atleast metalled
single lane carriage way (i.e., 3.8m) wide. The roads carry mixed traffic.
Other District Roads (ODR): these roads connect the village to other village or
the nearest district road, with ghat, river etc. these roads have a single lane and
carry mixed traffic.
Village Roads (VR): these roads, like other district roads, connect the village or
village or nearby district road. The roads carry mixed traffic.
6) Modified Classification of Road system by Third Road Development Plan:
Primary System (Expressways and National Highways)
Secondary System (State Highways and Major District
Roads) Tertiary System (Other District Roads and Village
Roads).
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7) Based on Urban Roads:
Arterial roads
Sub-arterialroads
Collector Streets
Local Streets
Arterial and Sub-arterial roads are primarily for through traffic on a
continuous route, but sub-arterials have a lower level of traffic mobility than the
arterials.
Collector streets provide access to arterial streets and they collect and distribute
traffic from and to local streets which provide access to abutting property.
ROAD PATTERNS:
There are various types of road patterns and each pattern has its own advantages
and limitations. The choice of the road pattern depends upon the various factors
such as:
Locality
Layout of the different towns, villages, industrial and production centres.
Planning Engineer.
The various road patterns may be classified as follows:
Rectangular or block pattern: In this, entire area is divided into rectangular
segments having a common central business and marketing area. This area has
all the services located in the central place. This pattern is not convenient or safe
from traffic operation point of view and it results into more number of accidents
at intersections. Eg: Chandigarh city.
Radial or star and block pattern: In this, roads radially emerge from the
central business area in all directions and between two built-up areas will be
there. The main advantage in this, central place is easy accessible from all the
directions. Eg: Nagpur
Radial or star and circular pattern: In this roads radiate in all the directions
and also circular ring roads are provided.
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Advantages: Traffic will not touch the heart of the city and it flows radially and
reaches the other radial road and thereby reducing the congestion in the centre of
the city. This ring road system is well suited for big cities where traffic problems
are more in the heart of the city. Eg: Connaught place in New Delhi.
Radial or star and grid pattern: It is very much similar to star and the circular
pattern expects the radial roads are connected by grids. In this pattern a grid is
formed around the central point which is a business centre. Eg: Nagpur road
plan.
Hexagonal pattern: In this entire zone of planning is divided into hexagonal
zones having separate marketing zone and central services surrounded by
hexagonal pattern of roads. Each hexagonal element is independent. At each
corner of hexagon three roads meet.
Minimum travel pattern: In this type, city is divided into number of nodal
points around a central portion by forming sectors. And each sector is divided
again in such a way that from each of the nodal centre, the distance to the central
place is minimum.
PLANNING SURVEYS:
Prior to the development of highways planning is required for any
engineering works, which is a basic requirement for a new project or for an
expansion. In all developing countries like India where, the resources are limited
and requirement is high then planning provides better utilization of funds in a
system.
Objective of Planning surveys:
Workout, the financial system and recommended changes in tax arrangements
and budget procedures, provide efficient, safe economics, comfortable and
speedy movement for goods and people.
Plan a road network for efficient traffic operation at minimum cost.
Plan for future requirements and improvements of roads in view of
developments and social needs.
Fix up datawise priorities for development of each road link based on their utilities.
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The planning surveys consist of the following studies:
Economic Studies: This study consists the following details:
Population and its distribution
Trend of population growth
Age and land products
Existing facilities
Per Capita income.
Financial Studies: This study involves collecting the details such as:
Sources of income
Living Standards
Resources from local levels
Factor trends in financial.
Traffic or road use studies: In this details collected are:
Traffic Volume/day, annual or daily traffic peak flow.
Origin and destination studies
Traffic flow patterns
Mass transportation facilities
Accidents, cause and cost analysis
Engineering studies: This
involves Topographic study
Soil details
Location and classification of existing roads
Road life studies
Specific problems in drainage constructions &
maintenance.
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MASTER PLAN:
Master plan is referred to as road development plan of a city;
district or a street or for whole country. It is an ideal plan showing full
development of the area at some future date. It serves as the guide for the
plan to improve some of the existing roads and to plan the network of new
roads.
It helps in controlling the industrial, commercial and agricultural
and habitat growth in a systematic way of that area. It gives a perceptive
picture of a fully developed area in a plan and scientific way.
Stages in the preparation of master plan:
Data Collection: It includes data regarding existing land use,
industrial and agricultural growth, population, traffic flow,
topography, future trends.
Preparation of draft plan and invite suggestions and comments from
public and experts.
Revision of draft plan in view of the discussions and comments
from experts and public.
Comparison of various alternate proposals of road
system and finding out the sequence in which the
master plan will be implemented
In India targeted road lengths were fixed in various road plans, based on
population, area and agricultural and industrial products. The same way it may be taken
as a guide to decide the total length of road system in each alternate proposal while
preparing a master plan for a town or locality.
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Preparation of Plans:
Plan-1: This plan should give the topographical details related to existing road
network, drainage, structures, towns and villages with population, agricultural,
industrial and commercial activities.
Plan-2: Should give the details pertaining to the distribution of
population
Plan-3: Should indicate the location of places with productivity.
Plan-4: Should indicate the existing network of roads and proposals
received. Ultimately, the Master plan is the one to be implemented.
SATURATION SYSTEM:
In this system optimum road length is calculated for an area based on the
concept of attaining maximum utility per unit length of the road. This is also
called as maximum utility system.
Factors to attain maximum utility per unit length are:
Population served by the road network
Productivity (industrial and agricultural) served by the road network.
The various steps to be taken to obtain maximum utility per unit length are:
Population factors or units: Since, the area under consideration consists of
villages and towns with different population these are grouped into some
convenient population range and some reasoning values of utility units to each
range of population serve are assigned.
Population less than 500, utility unit = 0.25
501 to 1001, utility unit = 0.50
1001 to 2000, utility unit = 1.00
2001 to 5000, utility unit = 2.00 etc.
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Productivity Factors or units: The total agricultural and industrial products
served by each road system are worked out and the productivity served may be
assigned appropriate values of utility units per unit weight.
Optimum Road length: Based on the master plan the targeted road length is
fixed for the country on the basis of area or population and production or both.
And the same may be taken as a guide to decide the total length of the road
system in each proposal.
ROAD DEVELOPMENT IN INDIA:
The first attempt for proper planning of the highway development programme in
India on a long term basis was made at the Nagpur Conference in 1943. After, the
completion of the Nagpur Road Plan targets, the Second Twenty year Plan was drawn
for the period 1961-1981. The Third Twenty Year Road Development Plan for the
period 1981-2001 was approved only by the year 1984.
First 20-Year Road Plan (Nagpur Road plan):
This plan was formed in the year 1943 at Nagpur. The plan period was from
1943-1963.Two plan formulae were finalized at the Nagpur Conference for deciding
two categories of road length for the country as a whole as well as for individual areas
(like district). This was the first attempt for highway planning in India. The two plan
formulae assumed the Star and Grid pattern of road network. Hence, the two formulae
are also called “Star and Grid Formulae”.
Salient Features of Nagpur Road Plan:
The roads are classified as,
o Primary System (NH/Expressways)
o Secondary System (SH/MDR)
o Tertiary System(ODR/VR)
Construction and Maintenance of NH was assigned to Central
government It aims for 2, 00,000km of bituminous road and 3,
32,700km of other types.
The formulae were based on star and grid pattern of road network and were
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considered as two equations:
I –Category: NH/SH/MDR
II-Category: ODR/VR
NH/SH/MDR are meant to provide main grids and ODR/VR as internal road
system the development allowance is 15%
The length of railway track was deducted.
Second Twenty Year Road Plan (Bombay Road Plan):
As the target road length of Nagpur road plan was completed nearly
earlier in 1961 a long term plan was initiated for twenty year period which was
initiated by IRC. Hence, the second twenty year road plan came into picture which
was drawn for the period of 1961-81. The second twenty year road plan was
envisaged overall road length of 10, 57,330 km by the year 1981.
Salient Features of Second 20 year Road Plan:
Aim to provide 32km/100 sq km area
Every town with population above 2000 in plains should be connected by
a bituminous road or metalled road.
>2000 in plains
>1000 in semi-hill area
>500 in hilly area
1600 km length of expressways was proposed
Development allowance is 5% only
Length of railway track was not deducted.
Five equations are given to find NH/SH/MDR/ODR/VR.
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Comparison of I and II 20-year plans:
First 20-year Plan Second 20-year Plan
Areas is divided into two types
namely, developed and semi-
developed developed areas
Areas is divided into three
types namely, developed; semi-
and undeveloped area.
Two equations are given to
find NH/SH/MDR/ODR/VR
Five equations are given to
find NH/SH/MDR/ODR/VR.
Aim is 16km/100 sq km Aim is 32km/100 sq km.
Development allowance is Development allowance is
15% No express ways 5%. 1600km of expressway
was included.
Length of Railway track was deducted Not deducte
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Unit 3 Highway alignment
Alignment
The position or the layout of the central line of the highway on the ground is called the
alignment. Horizontal alignment includes straight and curved paths. Vertical alignment
includes level and gradients. Alignment decision is important because a bad alignment
will enhance the construction, maintenance and vehicle operating cost. Once an alignment
is fixed and constructed, it is not easy to change it due to increase in cost of adjoining land
and construction of costly structures by the roadside
Requirements
The requirements of an ideal alignment are
The alignment between two terminal stations should be short and as far as possible
be straight, but due to some practical considerations deviations may be needed.
The alignment should be easy to construct and maintain. It should be easy for the
operation of vehicles. So to the maximum extend easy gradients and curves should
be provided.
It should be safe both from the construction and operating point of view especially
at slopes, embankments, and cutting. It should have safe geometric features.
The alignment should be economical and it can be considered so only when the
initial cost, maintenance cost, and operating cost is minimum.
Factors controlling alignment
We have seen the requirements of an alignment. But it is not always possible to satisfy al
these requirements. Hence we have to make a judicial choice considering all the factors.
The various factors that control the alignment are as follows:
Obligatory points these are the control points governing the highway alignment.
These points are classified into two categories. Points through which it should pass
and points through which it should not pass. Some of the examples are:
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Bridge site: The Bridge can be located only where the river has straight and
permanent path and also where the abutment and pier can be strongly founded.
The road approach to the bridge should not be curved and skew crossing should be
avoided as possible. Thus to locate a bridge the highway alignment may be
changed.
Mountain: While the alignment passes through a mountain, the various alternatives
are to either
Construct a tunnel or to go round the hills. The suitability of the alternative
depends on factors like topography, site conditions and construction and operation
cost.
Intermediate town: The alignment may be slightly deviated to connect an
intermediate town or village nearby. These were some of the obligatory points
through which the alignment should pass. Coming to the second category that is
the points through which the alignment should not pass are:
Religious places: These have been protected by the law from being acquired for
any purpose. Therefore, these points should be avoided while aligning.
Very costly structures: Acquiring such structures means heavy compensation
which would result in an increase in initial cost. So the alignment may be deviated
not to pass through that point.
Lakes/ponds etc: The presence of a lake or pond on the alignment path would
also Necessitate deviation of the alignment.
Traffic: The alignment should suit the traffic requirements. Based on the origin-
destination data of the area, the desire lines should be drawn. The new alignment
should be drawn keeping in view the desire lines, traffic flow pattern etc.
Geometric design: Geometric design factors such as gradient, radius of curve,
sight distance etc. also governs the alignment of the highway. To keep the radius
of curve minimum, it may be required to change the alignment of the highway.
The alignments should be finalized such that the obstructions to visibility do not
restrict the minimum requirements of sight distance. The design standards vary
with the class of road and the terrain and accordingly the highway should be
aligned.
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Economy: The alignment finalized should be economical. All the three costs i.e.
construction, maintenance, and operating cost should be minimum. The
construction cost can be decreased much if it is possible to maintain a balance
between cutting and filling. Also try to avoid very high embankments and very
deep cuttings as the construction cost will be very higher in these cases.
Other considerations: various other factors that govern the alignment are
drainage considerations, political factors and monotony.
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UNIT 4 HIGHWAY GEOMETRIC DESIGN I & II
Introduction
The geometric design of highways deals with the dimensions and layout of visible
features of the highway. The emphasis of the geometric design is to address the
requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. The
features normally considered are the cross section elements, sight distance consideration,
horizontal curvature, gradients, and intersection.
Factors affecting geometric design
Factors affecting the geometric designs are as follows
Design speed:
o Design speed is the single most important factor that affects the geometric design.
It directly affects the sight distance, horizontal curve, and the length of vertical
curves. Since the speed of vehicles vary with driver, terrain etc, a design speed is
adopted for all the geometric design.
Topography:
o It is easier to construct roads with required standards for a plain terrain. However,
for a given design speed, the construction cost increases multi form with the
gradient and the terrain.
Traffic:
It will be uneconomical to design the road for peak traffic flow. Therefore a
reasonable value of traffic volume is selected as the design hourly volume which is
determined from the various traffic data collected.
Environmental:
o Factors like air pollution, noise pollution etc. should be given due consideration in
the geometric design of roads.
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Economy:
o The design adopted should be economical as far as possible. It should match with
the funds allotted for capital cost and maintenance cost.
Others:
o Geometric design should be such that the aesthetics of the region is not affected
Cross sectional elements
The feature of the cross-section of the pavement influences the life of the pavement as
well as the riding comfort and safety.
Pavement surface characteristics
For a safe and comfortable driving four aspects of the pavement surface are
important;
Friction
Friction between the wheel and the pavement surface is a crucial factor in the
design of horizontal curves and thus the safe operating speed. Further, it also affects the
acceleration and deceleration ability of vehicles. Lack of adequate friction can cause
skidding or slipping of vehicles.
Various factors that affect friction are:
Type of the pavement (like bituminous, concrete, or
gravel), Condition of the pavement (dry or wet, hot or
cold, etc),
Condition of the tire (new or old),
and Speed and load of the vehicle.
The choice of the value of f is a very complicated issue since it depends on many
variables. IRC suggests the coefficient of longitudinal friction as 0.35-0.4 depending on
the speed and coefficient of later friction as 0.15.
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Unevenness
It affects the vehicle operating cost, speed, riding comfort, safety, fuel
consumption and wear and tear of tires. Unevenness index is a measure of unevenness
which is the cumulative measure of vertical undulation of the pavement surface recorded
per unit horizontal length of the road.
Light reaction
White roads have good visibility at night, but caused glare during day
time. Black roads has no glare during day, but has poor visibility at
night
Drainage
The pavement surface should be absolutely impermeable to prevent seepage of
water into the pavement layers.
Camber
Camber or cant is the cross slope provided to raise middle of the road surface in
the transverse direction to drain off rain water from road surface.
The objectives of providing camber are:
Surface protection especially for gravel and bituminous
roads Sub-grade protection by proper drainage
Quick drying of pavement which in turn increases safety
Too steep slope is undesirable for it will erode the surface. Camber is measured in 1 in
n or n% (Eg. 1 in 50 or2%) and the value depends on the type of pavement surface.
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Width of carriage way
Width of the carriage way or the width of the pavement depends on the width of the traffic
lane and number of lanes. Width of a traffic lane depends on the width of the vehicle and
the clearance. Side clearance improves operating speed and safety.
Kerbs
Kerbs indicate the boundary between the carriage way and the shoulder or
islands or footpaths. Different types of kerbs are (Figure 12:3):
Low or mountable kerbs:
These types of kerbs are provided such that they encourage the traffic to remain in
the through traffic lanes and also allow the driver to enter the shoulder area with little
difficulty..
Semi-barrier type kerbs:
When the pedestrian traffic is high, these kerbs are provided. Their height is 15 cm
above the pavement edge.
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Barrier type kerbs:
They are designed to discourage vehicles from leaving the pavement. They
are provided when there is considerable amount of pedestrian traffic. They are
placed at a height of 20 cm above the pavement edge with a steep batter.
Submerged kerbs:
They are used in rural roads. The kerbs are provided at pavement edges between
the pavement edge and shoulders. They provide lateral confinement and stability to the
pavement.
Road margins
The portion of the road beyond the carriageway and on the roadway can be
generally called road margin. Various elements that form the road margins are given
below.
Shoulders
A shoulder are provided along the road edge and is intended for accommodation of
stopped vehicles, serve as an emergency lane for vehicles and provide lateral support for
base and surface courses. The shoulder should be strong enough to bear the weight of a
fully loaded truck even in wet conditions.
Parking lanes
Parking lanes are provided in urban lanes for side parking. Parallel parking is
preferred because it is safe for the vehicles moving in the road. The parking lane should
have a minimum of 3.0 m width in the case of parallel parking .
Bus-bays
Bus bays are provided by recessing the kerbs for bus stops. They are provided so that
they do not obstruct the movement of vehicles in the carriage way.
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Service roads
Service roads or frontage roads give access to access controlled highways
like freeways and expressways. They run parallel to the highway and will be usually
isolated by a separator and access to the highway will be provided only at selected
points.
Cycle track
Cycle tracks are provided in urban areas when the volume of cycle traffic is
high Minimum width of 2 meter is required, which may be increased by 1 meter for
every additional track.
Footpath
Footpaths are exclusive right of way to pedestrians, especially in urban areas.
They are provided for the safety of the pedestrians when both the pedestrian traffic
and vehicular traffic is high.
Guard rails
They are provided at the edge of the shoulder usually when the road is on an
embankment. They serve to prevent the vehicles from running On the
embankment, especially when the height of the fill exceeds 3 m.
Width of formation
Width of formation or roadway width is the sum of the widths of pavements or
carriage way including separators and shoulders. This does not include the extra
land in formation/cutting. The values suggested by IRC are given in Table
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Right of way
Right of way (ROW) or land width is the width of land acquired for the road, along its
alignment. It should be adequate to accommodate all the cross-sectional elements of the
highway and may reasonably provide for future development.:
Width of formation: It depends on the category of the highway and width of roadway and
road margins.
Height of embankment or depth of cutting: It is governed by the topography and the
vertical alignment.
Side slopes of embankment or cutting: It depends on the height of the slope, soil type etc.
Drainage system and their size which depends on rainfall, topography etc.
The importance of reserved land is emphasized by the following Extra width of
land is available for the construction of roadside facilities.
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Figure: A typical Right of way
Sight distance
The safe and efficient operation of vehicles on the road depends very much on the
visibility of the road ahead of the driver.
Types of sight distance
Sight distance available from a point is the actual distance along the road surface, over
which a driver from a specified height above the carriage way has visibility of stationary
or moving objects. Three sight distance situations are considered for design:
Stopping sight distance (SSD) or the absolute minimum sight distance
Intermediate sight distance (ISD) is the defined as twice SSD Overtaking
sight distance (OSD) for safe overtaking operation
Head light sight distance is the distance visible to a driver during night driving under
the illumination of head light
Safe sight distance to enter into an intersection
The most important consideration in all these is that at all times the driver travelling at
the design speed of the highway must have sufficient carriageway distance within his line
of vision to allow him to stop his vehicle before colliding with a slowly moving or
stationary object appearing suddenly in his own traffic lane. The computation of sight
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distance depends on:
Reaction time of the driver
Reaction time of a driver is the time taken from the instant the object is visible to the
driver to the instant when the brakes are applied. The total reaction time may be split up
into four components based on PIEV theory. In practice, all these times are usually
combined into a total perception- reaction time suitable for design purposes as well as for
easy measurement.
Speed of the vehicle
The speed of the vehicle very much affects the sight distance. Higher the speed, more
time will be required to stop the vehicle. Hence it is evident that, as the speed increases,
sight distance also increases.
Efficiency of brakes
The efficiency of the brakes depends upon the age of the vehicle, vehicle
characteristics etc. If the brake efficiency is 100%, the vehicle will stop the moment the
brakes are applied. But practically, it is not possible to achieve 100% brake efficiency.
Frictional resistance between the tire and the road
The frictional resistance between the tire and road plays an important role to bring the
vehicle to stop. When the frictional resistance is more, the vehicles stop immediately.
Thus sight required will be less. No separate provision for brake efficiency is provided
while computing the sight distance.
Gradient of the road
Gradient of the road also affects the sight distance. While climbing up a gradient, the
vehicle can stop immediately. Therefore sight distance required is less.
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Stopping sight distance
SSD is the minimum sight distance available on a highway at any spot having
sufficient length to enable the driver to stop a vehicle traveling at design speed, safely
without collision with any other obstruction.
Lag distance is the distance the vehicle traveled during the reaction time t and is given
by vt, where v is the
velocity in m/sec.
Braking distance is the distance traveled by the vehicle during braking operation. For a
levelroad this is obtained by equating the work done in stopping the vehicle and the
kinetic energy of the vehicle. If F is the maximum frictional force developed and the
braking distance is l, then work done against friction in stopping the vehicle is
Fl = fWl where W is the total weight of the vehicle. The
kinetic energy at the design speed is
Therefore, the SSD = lag distance + braking distance and given by:
SSD = vt + v2/
2gf
Where v is the design speed in m/sec, t is the reaction time in sec, g is the acceleration
due to gravity and f is the coefficient of friction. The coefficient of friction f is given
below for
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Table: Coefficient of longitudinal friction
When there is an ascending gradient of say +n%, the component of gravity adds to
braking action and hence braking distance is decreased. The component of gravity acting
parallel to the surface which adds to the braking force is equal to W sin α = W tanα = Wn=100. Equating kinetic energy and work done:
Similarly the braking distance can be derived for a descending gradient.
Therefore the general equation is given by Equation
Overtaking sight distance
The overtaking sight distance is the minimum distance open to the vision of the
driver of a vehicle intending to overtake the slow vehicle ahead safely against the traffic
in the opposite direction. The overtaking sight distance or passing sight distance is
measured along the center line of the road over which a driver with his eye level 1.2m
above the road surface can see the top of an object 1.2 m above the road surface. The
factors that affect the OSD are: Velocities of the overtaking vehicle, overtaken vehicle
and of the vehicle coming in the opposite direction.
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Spacing between vehicles, which in-turn depends on the speed
d1 the distance traveled by overtaking vehicle A during the reaction time t = t1 - t0
d2 the distance traveled by the vehicle during the actual overtaking operation T = t3 - t1
d3 is the distance traveled by on-coming vehicle C during the overtaking operation (T).
Therefore:
OSD = d1 + d2 + d3
It is assumed that the vehicle A is forced to reduce its speed to vb, the speed of the slow
moving vehicle Band travels behind it during the reaction time t of the driver. So d1 is
given by:
d1 = vbt
Then the vehicle A starts to accelerate, shifts the lane, overtake and shift back to the
original lane. The vehicle A maintains the spacing s before and after overtaking. The
spacing s in m is given by:
s = 0:7vb + 6
Let T be the duration of actual overtaking. The distance traveled by B during the
overtaking operation is2s+vbT. Also, during this time, vehicle A accelerated from initial
velocity vb and overtaking is completed while reaching final velocity v. Hence the
distance traveled is given by:
The distance traveled by the vehicle C moving at design speed v m=sec during
overtaking operation is given by:
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The overtaking sight distance is (Figure)
Where vb is the velocity of the slow moving vehicle in m=sec2, t the reaction time of the
driver in sec, s is the spacing between the two vehicle in m given by equation and a is the
overtaking vehicles acceleration in m=sec2. In case the speed of the overtaken vehicle is
not given, it can be assumed that it moves 16 kmph slower the design speed. The
acceleration values of the fast vehicle depends on its speed and given in Table
Table : Maximum overtaking acceleration at different speeds
Overtaking zones
Overtaking zones are provided when OSD cannot be provided throughout the
length of the highway. These are zones dedicated for overtaking operation, marked with
wide roads. The desirable length of overtaking zones is 5 time OSD and the minimum is
three times OSD (Figure 13:2).
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Sight distance at intersections
At intersections where two or more roads meet, visibility should be
provided for the drivers approaching the intersection from either sides. They
should be able to perceive a hazard and stop the vehicle if required.:
o Enabling approaching vehicle to change the
speed o Enabling approaching vehicle to stop
o Enabling stopped vehicle to cross a main road
Horizontal curve
The presence of horizontal curve imparts centrifugal force which is reactive force
acting outward on a vehicle negotiating it. Centrifugal force depends on speed and
radius of the horizontal curve and is counteracted to a certain extent by transverse
friction between the tyre and pavement surface. On a curved road, this force tends
to cause the vehicle to overrun or to slide outward from the centre of road
curvature. The centrifugal force P in kg=m2 is given by
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P =Wv2/gR
where W is the weight of the vehicle in kg, v is the speed of the vehicle in m=sec,
g is the acceleration due to gravity in m=sec2 and R is the radius of the curve in
m. The centrifugal ratio or the impact factor P/W is given by P/W=b/2h
The centrifugal force has two effects: a tendency to overturn the vehicle about the
outer wheels and a tendency for transverse skidding. Taking moments of the
forces with respect to
the other when the vehicle is just about to override is give as:
Ph = W b
2
At the equilibrium over turning is possible when
V2 = b gR 2h
And for safety the following condition must satisfy:
b/2h>v2/gR
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The second tendency of the vehicle is for transverse skidding. i.e. When the centrifugal
force P is greater than the maximum possible transverse skid resistance due to friction
between the pavement surface and tire. The transverse skid resistance (F) is given by:
F=FA+FB
= f(RA + RB)
= fW
where FA and FB is the fractional force at tire A and B, RA and RB is the reaction at
tire A and B, f is the lateral coefficient of friction and W is the weight of the vehicle.
This is counteracted by the centrifugal force (P), and equating:
P = fW or
P = i
At equilibrium, when skidding takes place (from equation14.2)
P = f = v2 W gR
If this equation is violated, the vehicle will overturn at the horizontal curve and if
equation 14.4 is violated, the vehicle will skid at the horizontal curve
Analysis of super-elevation
Super-elevation or cant or banking is the transverse slope provided at horizontal
curve to counteract the centrifugal force, by raising the outer edge of the pavement with
respect to the inner edge, throughout the length of the horizontal curve.
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Forces acting on a vehicle on horizontal curve of radius R m at a speed of v m/s
are:
P the centrifugal force acting horizontally out-wards through the center of
gravity, W the weight of the vehicle acting down-wards through the center of
gravity, and F the friction force between the wheels and the pavement, along the
surface inward.
At equilibrium, by resolving the forces parallel to the surface of the pavement we get,
At equilibrium, by resolving the forces parallel to the surface of the pavement we get,
P cosθ = W sin θ + FA + FB
= W sin θ + f (RA + RB)
= W sin θ + f (W cos θ + P sin θ)
where W is the weight of the vehicle, P is the centrifugal force, f is the coefficient of
friction, f is the transverse slope due to super elevation. Dividing by W cos θ, we get:
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Attainment of super-elevation
Elimination of the crown of the cambered section by:
Rotating the outer edge about the crown: The outer half of the cross slope is
rotated about the crown at a desired rate such that this surface falls on the same
plane as the inner half.
Rotation of the pavement cross section to attain full super elevation
There are two methods of attaining super elevation by rotating the pavement
Rotation about the center line : The pavement is rotated such that the inner edge is
depressed and the outer edge is raised both by half the total amount of super
elevation, i.e., by E=2 with respect to the centre
Rotation about the inner edge: Here the pavement is rotated raising the outer edge
as well as the centre such that the outer edge is raised by the full amount of
superelevation with respect to the inner edge.
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Mechanical widening
The reasons for the mechanical widening are: When a vehicle negotiates a
horizontal curve, the rear wheels follow a path of shorter radius than the front wheels as
shown in figure. this phenomenon is called off tracking, and has the effect of increasing
the effective width of a road space required by the vehicle. Therefore, to provide the same
clearance between vehicles travelling in opposite direction on curved roads as is provided
on straight sections, there must be extra width of carriageway available.. The expression
for extra width can be derived from the simple geometry of a vehicle at a horizontal curve
as shown in figure Let R1 is the radius of the outer track line of the rear wheel, R2 is the
radius of the outer track line of the front wheel l is the distance between the front and rear
wheel, n is the number of lanes, then the mechanical widening Wm (is derive below:
If the road has n lanes, the extra widening should be provided on each lane. Therefore,
the extra widening of a road with n lanes is given
by,
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Psychological widening
Widening of pavements has to be done for some psychological reasons also. There is a
tendency for the drivers to drive close to the edges of the pavement on curves. Some extra
space is to be provided for more clearance for the crossing and overtaking operations on
curves. IRC proposed an empirical relation for the psychological widening at horizontal
curves Wps
Horizontal Transition Curves
Transition curve is provided to change the horizontal alignment from straight to
circular curve gradually and has a radius which decreases from infinity at the straight end
(tangent point) to the desired radius of the circular curve at the other end (curve point)
There are five objectives for providing transition curve and are given below:
1. To introduce gradually the centrifugal force between the tangent point and the
beginning of the circular curve, avoiding sudden jerk on the vehicle. This increases the
comfort of passengers. To enable the driver turn the steering gradually for his own comfort and security
Type of transition curve
Different types of transition curves are spiral or clothoid, cubic parabola, and
Lemniscates. IRC recommends spiral as the transition curve because:
1. It full fills the requirement of an ideal transition curve, that is;
(a) rate of change or centrifugal acceleration is consistent (smooth) and
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(b) Radius of the transition curve is 1 at the straight edge and changes to R at the curve
point (Ls / 1R) and calculation and field implementation is very easy.
Length of transition curve
The length of the transition curve should be determined as the maximum of the
following three criteria: rate of change of centrifugal acceleration, rate of change of super
elevation, and an empirical formula given by IRC.
1. Rate of change of centrifugal acceleration
At the tangent point, radius is infinity and hence centrifugal acceleration is zero. At
the end of the transition, the radius R has minimum value R. If c is the rate of change of
centrifugal acceleration, it can be written as:
The length of the transition curve Ls1 in m is
Ls1 = V3
cR
where c is the rate of change of centrifugal acceleration given by an empirical
formula suggested by IRC as
c = ____80____ 75 + 3.6v
Cmin = 0:5; Cmax = 0:8:
2. Rate of introduction of super-elevation
Raise (E) of the outer edge with respect to inner edge is given
by E = eB = e(W +We). The rate of change of this raise from 0 to
E is achieved gradually with a gradient of 1 in N over the length
of the transition curve (typical range of N is 60-150). Therefore,
the length of the transition curve Ls2 is:
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Ls2 = Ne (W +We)
3. By empirical formula
IRC suggest the length of the transition curve is minimum for a plain and rolling terrain:
Ls3 = 35v2 R
Steep and hilly terrain is: Ls3 =12.96v2
R
And the shift is as:
S=(Ls) 2/24R
The length of the transition curve Ls is the maximum of equations
Ls = Max: (Ls1; Ls2 ;Ls3 )
Setback Distance
Setback distance m or the clearance distance is the distance required from the centerline
of a horizontal curve to an obstruction on the inner side of the curve to provide adequate
sight distance at a horizontal curve. The set back distance depends on:
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1. Sight distance (OSD, ISD and OSD),
2. Radius of the curve, and
3. Length of the curve.
Case (a) Ls < Lc For single lane roads:
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Case (b) Ls > Lc
For single lane:
Curve Resistance
When the vehicle negotiates a horizontal curve, the direction of rotation of the front and
the r ear wheels are different. The front wheels are turned to move the vehicle along the
curve, whereas the rear wheels seldom turn. This is illustrated in figure 16:4.The rear
wheels exert a tractive force T in the PQ direction. The tractive force available on the
front wheels is Tcosθ in the PS direction as shown in the figure 16:4. This is less than the actual tractive force, T applied. Hence, the loss of tractive force for a vehicle to negotiate
a horizontal curve is:
CR = T -- T cosα
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Vertical alignment
The vertical alignment of a road consists of gradients(straight lines in a vertical
plane) and vertical curves. The vertical alignment is usually drawn as a profile, which is a
graph with elevation as vertical axis and the horizontal distance along the centre line of
the road as the the horizontal axis.
Gradient
Gradient is the rate of rise or fall along the length of the road with respect to the
horizontal. While aligning a highway, the gradient is decided designing the vertical curve.
Before finalising the gradients, the construction cost, vehicular operation cost and the
practical problems in the site also has to be considered.
Types of gradient
Many studies have shown that gradient upto seven percent can have considerable
effect on the speeds of the passenger cars. On the contrary, the speeds of the heavy
vehicles are considerably reduced when long gradients a sat as two percent is adopted.
Although, atter gradients are desirable, it is evident that the cost of construction will also
be very high.
Ruling gradient
The ruling gradient or the design gradient is the maximum gradient with which the
designer attempts to design the vertical profile of the road. This depends on the terrain,
length of the grade, speed, pulling power of the vehicle and the presence of the horizontal
curve. In atter terrain, it may be possible to provide at gradients, but in hilly terrain it is
not economical and sometimes not possible also.
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Minimum gradient
This is important only at locations where surface drainage is important. Camber
will take care of the lateral drainage. But the longitudinal drainage along the side drains
requires some slope for smooth flow of water.
Limiting gradient
This gradient is adopted when the ruling gradient results in enormous increase in
cost of construction. On rolling terrain and hilly terrain it may be frequently necessary to
adopt limiting gradient.
Exceptional gradient
Exceptional gradient are very steeper gradients given at unavoidable situations.
They should be limited for short stretches not exceeding about 100 meters at a stretch.
Summit curve
Summit curves are vertical curves with gradient upwards. They are formed when
two gradients meet as illustrated in figure below in any of the following four ways:
1. When a positive gradient meets another positive gradient
2. When positive gradient meets a at gradient
3. When an ascending gradient meets a descending gradient.
4. When a descending gradient meets another descending gradient
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Type of Summit Curve
Many curve forms can be used with satisfactory results; the common practice
has been to use parabolic curves in summit curves. This is primarily because of the
ease with it can be laid out as well as allowing a comfortable transition from one
gradient to another.
Length of the summit curve
The important design aspect of the summit curve is the determination of the length
of the curve which is parabolic. As noted earlier, the length of the curve is guided by the
sight distance consideration.
Distance .Let L is the length
Case a: Length of summit curve greater than sight distance
The situation when the sight distance is less than the length of the curve
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Case b: Length of summit curve less than sight distance
When stopping sight distance is considered the height of driver's eye above the road
surface (h1) is taken as 1.2 meters, and height of object above the pavement surface (h2)
is taken as 0.15 meters. If overtaking sight distance is considered, then the value of
driver's eye height (h1) and the height of the obstruction (h2) are taken equal as 1.2
meters.
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Valley curve
Valley curve or sag curves are vertical curves with convexity downwards. They
are formed when two gradients meet as illustrated in figure below in any of the
following four ways:
1. When a descending gradient meets another descending gradient
2. When a descending gradient meets a at gradient 3. When a descending gradient meets an ascending gradient 4. When an ascending gradient meets another ascending gradient
Length of the valley curve
The valley curve is made fully transitional by providing two similar transition curves of
equal length The transitional curve is set out by a cubic parabola y = bx3 where b =
2N3/
L2 The length of the valley transition curve is designed based on two criteria:
1. Comfort criteria; that is allowable rate of change of centrifugal acceleration is limited
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to a comfortable level of about 0:6m=sec3.
2. Safety criteria; that is the driver should have adequate headlight sight distance at any
part of the country.
Comfort criteria
The length of the valley curve based on the rate of change of centrifugal
acceleration that will ensure comfort: Let c is the rate of change of acceleration, R the
minimum radius of
the curve, v is the design speed and t is the time, then c is given as:
Ls = v3/CR
For a cubic parabola, the value of R for length Ls is given by:
R = Ls N
Safety criteria
Length of the valley curve for headlight distance may be determined for two conditions:
length of the valley curve greater than stopping sight distance
and Length of the valley curve less than the stopping sight
distance.
Case 1: Length of valley curve greater than stopping sight distance (L > S)
The total length of valley curve L is greater than the stopping sight distance SSD.
The sight distance available will be minimum when the vehicle is in the lowest point in
the valley. This is because the beginning of the curve will have infinite radius and the
bottom of the curve will have minimum radius which is a property of the transition curve.
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Where L is the total length of valley curve, N is the deviation angle in radians or tangent
of the deviation angle or the algebraic difference in grades, and c is the allowable rate of
change of centrifugal acceleration which may be taken as 0:6m/sec3.
Where N is the deviation angle in radians, h1 is the height of headlight beam, α is the head beam inclination in degrees and S is the sight distance. The inclination α is = 1 degree.
Case 2 Length of valley curve less than stopping sight distance (L < S)
The length of the curve L is less than SSD. In this case the minimum sight distance
is from the beginning of the curve. The important points are the beginning of the curve
and the bottom most part of the curve. If the vehicle is at the bottom of the curve, then its
headlight beam will reach far beyond the endpoint of the curve whereas, if the vehicle is
at the beginning of the curve, then the headlight beam will hit just outside the curve.
Therefore, the length of the curve is derived by assuming the vehicle at the beginning of
the curve. The case is shown in figure below.
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The gradients are very small and are acceptable for all practical purposes. We will not
be able to know prior to which case to be adopted. Therefore both has to be calculated
and the one which satisfies the condition is adopted.
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UNIT 5 PAVEMENT MATERIALS
Introduction
Subgrade soil
Subgrade soil is an integral part of the road pavement structure which directly
receives the traffic load from the pavement layers. The subgrade soil and its properties are
important in the design of pavement structure. The main function of the subgrade is to
give adequate support to the pavement and for this the subgrade should possess sufficient
stability under adverse climate and loading conditions.
The formation of waves, corrugations, rutting and shoving in black top pavements
and the phenomena of pumping, blowing and consequent cracking of cement concrete
pavements
are generally attributed due to the poor subgrade conditions.
Desirable Properties
The desirable properties of soil as a highway material are
Stability
Incompressibility
Permanency of strength
Minimum changes in volume and stability under adverse conditions of weather and
ground water
Good drainage, and
Ease of compaction.
The soil should possess adequate stability or resistance to permanent deformation
under loads, and should possess resistance to weathering, thus retaining the desired
subgrade support. Minimum variation in volume will ensure minimum variation in
differential
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Soil classification
1. Grain size analysis
According to size of grains soil is classified as gravel, sand, silt and clay. As per
Indian standard classification the limits of grain size are as follows.
Gravel Sand Silt Clay
C M F C M F C M F
0.6 0.2
0.02 0.006 0.006 0.002
2.0mm 0.06mm 0.002mm
Fraction of soils
Larger than 2.00mm size Gravel
Between 2.00mm – 0.06 mm size Sand
Between 0.06mm – 0.002 mm size Silt
Smaller than 0.002 size Clay
2. Highway Research Board (HRB) classification of soils
This is also called American Association of State Highway Officials (AASHO)
classification of Revised Public Roads Administration (PRA) soil classification system.
Soils are divided into seven groups A-I to A-7. A-I, A-2 and A-3 soils are granular soils,
percentage fines passing 0.074 mm sieve being less than 35. A-4, A-5, A-6 and A-7, soils
are fine grained or silt-clay soils, passing 0.074 mm sieve being greater than 35 percent.
A-1 soils are well graded mixture of stone fragments, gravel coarse sand, fine sand
and non-plastic or slightly plastic soil binder. The soils of this group are subdivided into
two subgroups, A- 1-a, consisting predominantly of stone fragments or gravel and A-I-b
consisting predominantly of coarse sand.
A-2 group of soils include a wide range of granular soils ranging from A- 1 to A-3
groups, consisting of granular soils and upto 35% fines of A-4, A-5, A-6 or A-7 groups.
Based on the fines content, the soils of A-2 groups are subdivided into subgroups A-2-4,
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A-2-5, A-2-6 and A-2-7.
A-3 soils consist mainly, uniformly graded medium or fine sand similar to beach
sand or desert blown sand. Stream-deposited mixtures of poorly graded fine sand with
some coarse sand and gravel are also included in this group.
A-4 soils are generally silty soils, non-plastic or moderately plastic in nature with
liquid limit and plasticity index values less than 40 and 10 respectively
A-5 soils are also silty soils with plasticity index less than 10%, but with liquid
limit values exceeding 40%. These include highly elastic or compressible, soils, usually
of diatomaceous of micaceous character.
A-6 group of soils are plastic clays, having high values of plasticity index
exceeding 10% and low values of liquid limit below 40%; they have high volume change
properties with variation in moisture content.
A-7 soils are also clayey soils as A-6 soils, but with high values of both liquid limit and
plasticity index
California Bearing Ratio (CBR) Test
This is a penetration test developed by the California division of
highway. For evaluating the stability of soil subgrade and other pavement
materials. The test results have been correlated with flexible pavement thickness
requirement for highway and airfield. CBR test may be conducted in the laboratory
on a prepared specimen in a mould or in situ in the field.
Laboratory CBR test
The laboratory CBR apparatus consists of
Cylindrical mould
Mould 150mm dia, 175mm height with 50mm collar height, detachable perforated
base with spacer disc of 148mm dia and 47.7mm thick is used to obtain a
specimen of exactly 127.3mm height.
Loading Machine
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Compression machine operated at a constant rate of 1.25mm/min.Loading frame
with cylindrical plunger 50mm dia & dial gauge for measuring the deformation
due to application of load.
Compaction rammer
Type of compaction No of layers Wt of hammer Fall (cm) No of blows
(kg)
Light compaction 3 2.6 31 56
Heavy compaction 5 4.89 45 56
Annular weight or surcharge weight
2.5 Kgs of surcharge wt of 147mm dia are placed on specimen both at the soaking
and testing of prepared samples.
Procedure:
CBR test may be performed on undisturbed soil specimens.
About 5kgs of soil is taken passing though 20mm IS sieve and retained on 4.75mm IS
sieve
The soil is mixed with water upto OMC.
The spacer disc is placed at the bottom of the mould over the base plate & a coarse
filter paper is placed over the spacer disc.
Then the moist soil sample is to be compacted over this in the mould by adopting
either IS light compaction or IS heavy compaction.
For IS heavy compaction 3 equal layers of compacted thickness about 44mm by
applying 56 evenly distributed blows from 2.6kgs rammer.
For IS heavy compaction 5 equal layers of compacted thickness about 26.5mm by
applying 56 evenly distributed blows from 4.89 kg rammer.
After compacting the last layer, The collar is removed and the excess soil above the
top of the mould is evenly trimmed off by means of straight edge (of 5mm thickness).
Clamps are removed ant the mould with compacted soil is lifted leaving below the
perforated base plate & the spacer disc which is removed.
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Then the mould with compacted soil is weighed
Filter paper is placed on the perforated base plate & the mould with compacted soil is
inverted & placed in position over the base plate.
Now the clamps of the base is tightened
Another filter paper is placed on the placed on the top surface of the sample & the
perforated plate with adjustable stem is placed over it.
Now surcharge weights of 2.5 or 5kgs are placed over the perforated plate & the
whole mould with the weights is placed in a water tank for soaking such that water
can enter the specimen both from the top & bottom.
The initial dial gauge readings is recorded & the test set up is kept undisturbed in the
water tank to allow soaking of the soil specimen for full 4 days or 96 hrs.
The final dial gauge reading is noted to measure the expansion & swelling of the
specimen due to soaking.
The swell measurement assembly is removed, the mould is taken out of the water tank
& the sample is allowed to drain in a perpendicular position for 15 min surcharge wt,
perforated plate with stem, filter paper are removed.
The mould with the soil subgrade is removed from the base plate & is weighed again
to determine the wt of water absorbed.
Then the specimen is clamped over base plate surcharge wt‟s are placed on specimens centrally such that the penetration test could be conducted.
The mould with base plate is placed under the penetration plunger of loading machine.
The penetration plunger is seated +at the centre of the specimen & is brought in
contact with the top surface of the soil sample by applying a seating load of 4kgs.
The dial gauge for measuring the penetration values of the plunger is fitted in
position The dial gauge of proving ring & the penetration dial gauge are set to 0.
The load is applied though the penetration plunger at a uniform rate of 1.5mm/min
The load reading are recorded at penetration reading 0, 0.5, 1.0, 1.5, 2, 2.5, 3, 4, 5,
7.5, 10 & 12.5mm.
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In case the load reading starts decreasing before 12.5mm penetration, the max load &
the corresponding penetration values are recorded.
After the final reading the load is released & the mould from loading machine.
The proving ring calibration factor is noted so that load dial gauge value can be
converted into the load in kg.
Calculation :
Swelling or expansion ratio is calculated from the
formula. Expansion ratio = (100 ( df – di))/h
Where,
df = Final dial gauge after soaking in mm
di = Initial dial gauge before soaking in
mm h = initial ht of the specimen in mm
Therefore, CBR= Load sustained by the specimen at 2.5 or 5mm penetration x
100
Load sustained by std specimen at corresponding penetration level
CBR at 2.5mm = P1(kg) x 100%
1370
CBR at 5mm = P2(kg) x 100%
2055
Generally CBR value @ 2.5mm penetration is higher & this value is adopted.
The initial upward concavity of the load penetration is due to the piston surface not
being fully in contact with top of the specimen.
Top layer of soaked soil being too soft.
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Modulus of subgrade reaction of soil
Plate bearing test
The plate bearing test has been devised to evaluate the supporting power of
subgrade or any other pavement layer by using plates of larger diameter.
Plate bearing test was originally meant to find the modulus of subgrade reaction in
the westergards‟s analysis for wheel load stresses in cement concrete pavement.
In the plate bearing test a compressive stress is applied to the soil or pavement layer
through rigid plates of relatively large size & the deflection are measurement for
various stress values.
The deflection level is generally limited to a low value of 1.25mm to 5mm.
Modulus subgrade reaction (k)
K may be defined as the pressure sustained per unit deformation of subgrade
at specified pressure level using specified plate size.
The standard palte size for finding K value is 75cm dia in same test a smaller
plate of 30cm dia is also used (75,60,45,30 & 22.5 cm dia).
Apparatus used
Bearing plate:
Mild steel of 75cm dia & 1.5 to 2.5 cm thickness.
Loading equipment:
Reaction frame or dead load applied may be measured either by a proving ring or dial
gauge assembly.
Settlement measurement:
It may be made by means of 3 or 4 dial gauge fixed on the periphery of the bearing plate
from an independent datum frame. Datum frame should be supported from the loaded
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area.
Procedure
At the test site, about 20cm top soil is removed & the site is leveled & the plate is
properly seated on the prepared surface.
The stiffening plates of decreasing dia are placed & the jack & proving ring assembly
are fitted to provide reaction against the frame.
3 or 4 dial gauges are fixed on the periphery of the palte from the independent datum
frame for measuring settlement.
A seating load of 0.07 kg/cm2 (320kgs for 75 dia) is applied & released after a few
sec. The settlement dial gauges reading are now noted corresponding to zero load.
A load is applied by means of jack sufficient to cause an average settlement of about
0.25mm.
When there is no perception increase in settlement or when the rate of settlement is
less than 0.025mm/min (case of clayey soil or wet soil), the reading of the settlement
dial gauge are noted & the avg settlement is found & the load is noted from the
proving ring dial reading.
The load is then increased till settlement increases to a further amount of about
0.25mm
& the avg settlement & load are found.
The procedure is repeated till the settlement reaches 0.175cm.
A graph is plotted with mean settlement versus mean bearing pressure (load/unitarea)
as shown in fig.
Bearing pressure settlement curve.
The pressure p (kg/cm2) corresponding to a settlement delta = 0.125cm (obtaines
from the graph shown above)
The modulus of subgrade reaction k is calculated from the relation.
K = P kg/cm2
0.125
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Correction for smaller plate size
In some cases the load capacity may not be adequate to cause 75cm dia plate to settle
0.175cm.
In such a case a plate of smaller dia (say 30cm) may be used.
Then K value should be found by applying a suitable correction for plate size.
Assuming the subgrade to be an elastic medium with modulus of elasticity E
(kg/cm2), the theoretical relationship of deformation (cm) under a rigid plate of radius
a (cm) is given by
Delta = 1.18Pa
E
But, K = P
D
Substitute the value of D in K
Therefore K = P x E
1.18 Pa K = E
1.18a
If the value of E is taken as constant for a soil, Then k x a = constant
i.e. Ka = ka or K = ka
A
Hence if the test is carried out with a smaller plate of radius a & the modulus of subgrade
reaction K is found.
Then the corrected value of modulus of subgrade reaction K for std plate of radius a, is
given by K = k1 a1
A
AGGREGATES
Introduction
Aggregates form the major portion of pavement structure and they form the prime
materials used in pavement construction. Aggregates have to bear stresses occurring due
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to the wheel loads on the pavement and on the surface course they also have to resist wear
due to abrasive action of traffic.
Strength
The aggregates to be used in road construction should be sufficiently strong to
withstand the stresses due to traffic wheel load. The aggregates which are to be used in
top layers of the pavements, particularly in the wearing course have to be capable of
with4jnhighs1cssesinaddItion to - wear and tear; hence they should possess sufficient
strength resistance to crushing.
Toughness
Aggregates in the pavements are also subjected to impact due to moving wheel
loads. Sever impact like hammering is quite move on water bound macadam roads where
stones protrude out especially after the monsoons.
Durability
The stone used in pavement construction should be durable and should resist
disintegration due to the action of weather. The property of the stones to withstand the
adverse action of weather may called soundness.
Shape of Aggregates
The size of the aggregates is first qualified by the size of square sieve opening
through which an aggregate may pass, and not by the shape. Aggregates which happen to
fall in a particular size range may have rounded, cubical, angular flaky or elongated shape
of particles. It is e and donated particles will have less strength and durability when
compared with cubical angular or rounded articles of the same Stone. Hence too flaky and
too much elongated aggregates should be avoided as far as possible.
Adhesion with Bitumen
The aggregates used in bituminous pavements should have less affinity with water
when compared with bituminous materials, otherwise the bituminous coating on the
aggregate will be stripped off in presence of water.
Tests for Road Aggregate
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In order to decide the suitability of the road stones for use in construction, the
following tests are carried out:
(a) Crushing test
(b) Abrasion test
(c) Impact test
(d) Soundness
(e) Shape test
(f) Specific gravity and water absorption test (g) Bitumen adhesion test
The essential features of these tests are discussed below. Separate tests are
available for testing cylindrical stone specimens and coarse aggregates for crushing,
abrasion and impact tests. But due to the difficulties of preparing cylindrical stone
specimen which need costly core drilling, cutting and polishing equipment, the use of
such tests are now limited. Testing of aggregates is easy and simulate the field condition
better, as such these are generally preferred.
BITUMINOUS MATERIALS
Introduction
Bituminous binders used in pavement construction works include both bitumen
and tar. Bitumen is a petroleum product obtained by the distillation of petroleum crude
where-as road tar is obtained by the destructive distillation of coal or wood. Both bitumen
and tar have similar appearance, black in colour though they have different
characteristics. Both these materials can be used for pavement works.
(i) paving bitumen from Assam petroleum, denoted as A-type and designated as
grades A35, A 90, etc.
(ii) paving bitumen from other sources denoted as S-type and designated as grades S
35, S 90, etc.
Types of Bituminous Materials
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Bituminous material used in highway construction may be broadly divided as
(i) Bitumen and
(ii) Tar
Bitumen may be further divided as petroleum asphalt or bitumen and native asphalt. There
are different forms in which native asphalts are available. Native asphalts are those which
occur in a pure or nearly pure state in nature. Native asphalts which are associated with a
large proportion of mineral matter are called rock asphalts.
Bitumen
Crude petroleum obtained from different places are quite different in their
composition. The portion of bituminous material present in the petroleum‟s may widely differ depending on the source. Almost all the crude petroleum‟s contain considerable amounts of water along with crude oil. Hence the petroleum should be dehydrated first
before carrying out the distillation. General types of distillation processes are fractional
distillation and
Tests on Bitumen
Bitumen is available in a variety of types and grades. To judge the suitability of
these binders various physical tests have been specified by agencies like ASTM, Asphalt
Institute, British Standards Institution and the ISI. These tests include penetration test,
ductility tests, softening point test and viscosity test. For classifying bitumen and studying
the performance of bituminous pavements, the penetration and ductility tests are essential.
The various tests on bituminous materials are
(a) Penetration tests (b) Ductility tests (c) Viscosity tests
(d) Float test (e) Specific gravity test (f) Softening point test
(g) Flash and Fire point test (h) Solubility test (i) Spot test
(j) Loss on heating test (k) Water content test
Cutback Bitumen
Cutback bitumen is defined as the bitumen, the viscosity of which has been reduced by a
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volatile dilutant. For use in surface dressings, some type of bitumen macadam and soil
bitumen it is necessary to have a fluid binder which can be mixed relatively at low
temperatures. Hence to increase fluidity of the bituminous binder at low temperatures the
binder is blended with a volatile solvent. After the cutback mix in construction work, the
volatile gets evaporated and the cutback develops the properties. The viscosity of the
cutback and rate of which it hardens on the road depend on the characteristics and
quantity of both bitumen and volatile oil used as the diluent. Cutback bitumens are
available in three types, namely,
(i) Rapid Curing (RC)
(ii) Medium Curing (MC) and
(iii) Slow Curing (SC)
This classification is based on the rate of curing or hardening after the application. The
grade of cutback or its fluidity is designed by a figure which follows the initials; as an
example RC-2 means that it is a rapid curing cutback of grade 2.The cutback with the
lowest viscosity is designated by numeral 0, such as RC-0 and SC-0. Suffix numerals 0, 1,
2, 3, 4 and 5 designate progressively thicker or more viscous cutbacks as the numbers
increase. This number indicates a definite viscosity irrespective of the type of cutback; in
other words, RC-2, MC-2 all have the same initial viscosity at a specified temperature.
The initial viscosity values (in seconds, standard tar viscometer) of various grades of
cutbacks as per ISI specifications are given in Table 6.7.
Thus lower grade cutbacks like RC-0, RC-l etc. would contain high prop solvent
when compared with higher grades like RC-4 or RC-5, RC-0 and MC-0 may contain
approximately 45 percent solvent and 55 percent bitumen, whereas, RC-5 and MC-5 may
contain approximately 15 percent solvent and 85 percent bitumen.
Rapid Curing Cutbacks are bitumens, fluxed or cutback with a petroleum Distillate such
as naphta or gasoline which will rapidly evaporate after using in construction, leaving the
bitumen binder. The grade of the R.C. cutback is governed by the proportion of the
solvent used. The penetration value of residue from distillation up to 3600C of RC
cutback bitumen is 80 to 120.
Medium curing cutbacks are bitumen fluxed to greater fluidity by blending with a
intermediate-boiling-point solvent like kerosene or light diesel oil. MC cutbacks evaporate
relatively at slow rate because the kerosene-range solvents will not evaporate
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rapidly as the
gasoline-range solvents used in the manufacture of RC cutbacks. Hence the designation
„medium curing‟ is given to this cutback type. MC products have good wetting properties
and so satisfactory coating of fine grain aggregate and sandy soils is possible.
Slow curing cutbacks are obtained either by blending bitumen with high-boiling-
point gas oil, or by controlling the rate of flow and temperature of the crude during the
first cycle of refining. SC cutbacks or wood soils harden or set way slowly as it is a semi
volatile material.
Various tests carried out on cut-backs bitumen are
(a) Viscosity tests at specified temperature using specified size of orifice.
(b) Distillation test to find distillation fractions, up to specified temperature and to
find the residue from distillation up to 360°C
(c) Penetration test, ductility test and test for matter soluble in carbon disulphide on
residue from distillation up to 360°C
(d) Flash point test on cutback using Pensky Martens closed type apparatus.
Bituminous Emulsion
A bitumen emulsion is liquid product in which a substantial amount of bitumen is
suspended in a finely divided condition in an aqueous medium and stabilized by means
of one or more suitable materials. An emulsion is a two phase system consisting of two
immiscible liquids; the one being dispersed as fine globules in the other.Usually, bitumen
or refined tar is broken up into fine globules and kept in suspension in water. A small
proportion of an emulsifier is used to facilitate the formation of dispersion and to keep
the globules of dispersed binder in suspension.
Some of the general properties of road emulsions are judged by the following tests
(i) Residue on Sieving: It is desirable to see that not more than 0.25 percent by w of
emulsion consists of particles greater than 0.15 mm diameter.
(ii) Stability to Mixing with Coarse Graded Aggregate: This test carried out to fit the
emulsion breaks down and coats the aggregate with bitumen too early before
mixing is complete.
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(iii) Stability to Mixing with Cement : This test is carried out to assess the stability
emulsions when the aggregate contains large proportions of fines.
(iv) Water Cement: To know the percentage water in the emulsion which depend the
type of the emulsion.
(v) Sedimentation: Some sedimentation may occur when a drum of emulsion is
standing before use, but on agitation, the emulsion redisperses and can be used.
(vi) Viscosity: The viscosity of emulsified bitumen should be low enough to be
sprayed through jets or to coat the aggregates in simple mixing.
Three types of bituminous emulsion are prepared, viz., (i) Rapid Setting (RS),
Medium Setting (MS) and (iii) Slow Setting (SS) types. Rapid Setting type emulsion is
suitable for surface dressing and penetration macadam type of construction. Medium
Setting type is used for premixing with coarse aggregates and Slow Setting type emulsion
is suitable for fine aggregate mixes.
Tar:
Tar is the viscous liquid obtained when natural organic materials such as wood and
coal carbonized or destructively distilled in the absence of air. Based on the material from
which tar is derived, it is referred to as wood tar or coal tar; the latter is more widely used
for road work because it is superior. Three stages for the production of road tar are
(i) Carbonization of coal to produce crude tar
(ii) Refining or distillation of crude tar and
(iii) Blending of distillation residue with distillate oil fraction to give the desired road
tar.
There are five grades of roads tars, viz., RT- I, RT-2, RT-3, RT-4 and RT-5,
based on their viscosity and other properties. RT-l has the lowest viscosity and is used
for surface painting under exceptionally cold weather as this has very low viscosity. RT-
2 is recommended for standard surface painting under normal Indian climatic
conditions. RT-3 may be used for surface painting, renewal coats and premixing chips
for top course and light carpets. RT-4 is generally used for premixing tar macadam in
base course. For grouting purposes RT-5 may be adopted, which has the highest
viscosity among the road tars.
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The various tests that are carried out on road tars are listed below
(i) Specific gravity test
(ii) Viscosity test on standard tar viscometer
(iii) Equiviscous temperature (EVT)
(iv) Softening point
(v) Softening point of residue
(vi) Float test
(vii) Water content
(viii) Distillation fraction on distillation upto 200°C, 200°C to 270°C and 270°C
to 3 30°C.
(ix) Phenols, percent by volume
(x) Naphthalefle, percent by weight
(xi) Matter insoluble in toluene, percent by weight
The requirements for the five grades of road tars based on the above test results are given
by the ISI. Bitumen and tar have black to dark brown colour. But bitumen is a petroleum
product whereas tar is produced by the destructive distillation of coal or wood.
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Comparison between tar & bitumen
Bitumen Tar
It has black to dark brown color It also has black to dark brown in color
Tar is produced by the destructive
It is natural petroleum product distillation
of coal or wool
It is soluble in carbon disulphide & in carbon Tar is soluble only in toluene
tetrachloride
It has better weather resisting property It has inferior weather resisting property
Bitumen are less temp susceptible Tar is more temp susceptible
Free carbon content is less Free carbon content is More
It neither binds the aggregate well nor retains It binds aggregate more easily & retain it
the presence of water better in the presence of water.
BITUMINOUS PAVING MIXES
Requirements of Bituminous Mixes
The mix design should aim at an economical blend, with proper gradation of
aggregates and adequate proportion of bitumen so as to fulfil the desired properties of
the mix. Bituminous concrete or asphaltic concrete is one of the highest and costliest
types of flexible pavement layers used in the surfacing course. The desirable properties
of a good bituminous mix are stability, durability, flexibility, skid resistance and
workability.
Mix design methods should aim at determining the properties of aggregates and
bituminous material which would give a mix having the following properties.
(i) Sufficient stability to satisfy the service requirements of the pavement and the
traffic conditions, without undue displacement
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Unit 6 Introduction to pavement design
A highway pavement is a structure consisting of superimposed layers of processed
materials above the natural soil sub-grade, whose primary function is to distribute the
applied vehicle loads to the sub-grade. The pavement structure should be able to provide
a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting
characteristics, and low noise pollution.
Requirements of a pavement
The pavement should meet the following requirements:
Sufficient thickness to distribute the wheel load stresses to a safe value on the
sub-grade soil
Structurally strong to withstand all types of stresses imposed
upon it Adequate coefficient of friction to prevent skidding of
vehicles
Smooth surface to provide comfort to road users even at high speed
Types of pavements
The pavements can be classified based on the structural performance into two,
flexible pavements and rigid pavements. In flexible pavements, wheel loads are
transferred by grain-to-grain contact of the aggregate through the granular structure. The
flexible pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous
road). On the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil
by flexural strength of the pavement and the pavement acts like a rigid plate (e.g. cement
concrete roads).
Flexible pavements
Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain
transfer through the points of contact in the granular structure (see Figure 19:1). The
wheel load acting on the pavement will be distributed to a wider area, and the stress
decreases with the depth. Taking advantage of this stress distribution characteristic
The lower layers will experience lesser magnitude of stress and less quality material can
be used. Flexible pavements are constructed using bituminous materials. These can be
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either in the form of surface treatments (such as bituminous surface treatments generally
found on low volume roads) or, asphalt concrete surface courses (generally used on high
volume roads such as national highways) pavement layer
Types of Flexible Pavements
The following types of construction have been used in flexible pavement:
Conventional layered flexible
pavement, Full - depth asphalt
pavement, and
Contained rock asphalt mat (CRAM).
Conventional flexible pavements are layered systems with high quality expensive
materials are placed in the top where stresses are high, and low quality cheap materials
are placed in lower layers.
Full - depth asphalt pavements are constructed by placing bituminous layers directly on
the soil subgrade. This is more suitable when there is high traffic and local materials are
not available.
Contained rock asphalt mats are constructed by placing dense/open graded aggregate
layers in between two asphalt layers. Modified dense graded asphalt concrete is placed
above the sub-grade will significantly reduce the vertical compressive strain on soil sub-
grade and protect from surface water
Rigid pavements
Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a
wider area below. A typical cross section of the rigid pavement is shown in Figure below
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Compared to flexible pavement, rigid pavements are placed either directly on the prepared
sub-grade or on a single layer of granular or stabilized material.
Since there is only one layer of material between the concrete and the sub-grade, this layer
can be called as base or sub-base course. In rigid pavement, load is distributed by the slab
action, and the pavement behaves like an elastic plate resting on a viscous medium Rigid
pavements are constructed by Portland cement concrete (PCC) and should be analyzed by
plate theory instead of layer theory.
Types of Rigid Pavements
Rigid pavements can be classified into four types:
Jointed plain concrete pavement (JPCP),
Jointed rei forced concrete pavement (JRCP),
Continuous reinforced concrete pavement (CRCP),
and Pre-stressed concrete pavement (PCP).
Jointed Plain Concrete Pavement is plain cement concrete pavements constructed
withclosely spaced contraction joints. Dowel bars or aggregate interlocks are normally
used for load transfer across joints. They normally has a joint spacing of 5 to 10m.
Jointed Reinforced Concrete Pavement Although reinforcements do not improve
thestructural capacity significantly, they can drastically increase the joint spacing to 10 to
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30m. Dowel bars are required for load transfer. Reinforcements help to keep the slab
together even after cracks.Continuous Reinforced Concrete Pavement Complete
elimination of joints are achieved by reinforcement.
Factors affecting pavement design
Traffic and loading
Traffic is the most important factor in the pavement design. The key factors
include contact pressure, wheel load, axle configuration, moving loads, load, and load
repetitions.
Contact pressure
The tire pressure is an important factor, as it determines the contact area and the
contact pressure between the wheel and the pavement surface. Even though the shape of
the contact area is elliptical, for sake of simplicity in analysis, a circular area is often
considered.
Wheel load
The next important factor is the wheel load which determines the depth of the
pavement required to ensure that the subgrade soil is not failed. Wheel configuration
affects the stress distribution and deflection within a pavement. Many commercial
vehicles have dual rear wheels which ensure that the contact pressure is within the limits.
The normal practice is to convert dual wheel into an equivalent single wheel load so that
the analysis is made simpler.
Axle configuration
The load carrying capacity of the commercial vehicle is further enhanced by the
introduction of multiple axles.
Moving loads
The damage to the pavement is much higher if the vehicle is moving at creep
speed. Many studies show that when the speed is increased from 2 km/hr to 24 km/hr, the
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stresses and deflection reduced by 40 per cent.
Repetition of Loads
The influence of traffic on pavement not only depends on the magnitude of the
wheel load, but also on the frequency of the load applications. Each load application
causes some deformation and the total deformation is the summation of all these
Environmental factors
Environmental factors affect the performance of the pavement materials and cause
various damages. Environmental factors that affect pavement are of two types,
temperature and precipitation.
Equivalent single wheel load
To carry maximum load within the specified limit and to carry greater load, dual
wheel, or dual tandem assembly is often used. Equivalent single wheel load (ESWL) is
the single wheel load having the same contact pressure, which produces same value of
maximum stress, deflection, tensile stress or contact pressure at the desired depth. The
procedure of finding the ESWL for equal stress criteria is provided below. This is a semi-
rational method, known as Boyd and Foster method, based on the following assumptions:
equalancy concept is based on equal stress; contact area is circular; influence angle is
450; and soil medium is elastic, homogeneous, and isotropic half space.
Where P is the wheel load, S is the center to center distance between the two wheels, d is
the clear distance between two wheels, and z is the desired depth.
Equivalent single axle load
Vehicles can have many axles which will distribute the load into different axles,
and in turn to the pavement through the wheels. A standard truck has two axles, front axle
with two wheels and rear axle with four wheels. But to carry large loads multiple axles
are provided. Since the design of flexible pavements is by layered theory, only the wheels
on one side needed to be considered. On the other hand, the design of rigid pavement is
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by plate theory and hence the wheel load on both sides of axle need to be considered.
Legal axle load:
Repetition of axle loads:
The deformation of pavement due to a single application of axle load may be small
but due to repeated application of load there would be accumulation of unrecovered or
permanent deformation which results in failure of pavement.
Equivalent axle load factor:
An equivalent axle load factor (EALF) defines the damage per pass to a pavement
by the ith type of axle relative to the damage per pass of a standard axle load. While
_finding the EALF, the failure criterion is important. Two types of failure criteria‟s are commonly adopted: fatigue cracking and rutting. The fatigue cracking model has the
following form:
Where, Nf is the number of load repetition for a certain percentage of
cracking, _t is the tensile strain at the
bottom of the binder course, E is the modulus of elasticity, and f1; f2; f3 are
constants. If we consider fatigue
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cracking as failure criteria, and a typical value of 4 for f2, then:
Where, i indicate Ith
vehicle, and std indicate the standard axle. Now if we assume
that the strain is proportional to the wheel load,
Similar results can be obtained if rutting model is used, which is:
where Nd is the permissible design rut depth (say 20mm), s the compressive strain at the
top of the subgrade,
and f4; f5 are constants. Once we have the EALF, then we can get the ESAL as given
below. Equivalent single axle load, ESAL =
Where, m is the number of axle load groups, Fi is the EALF for ith
axle load group, and
ni is the number of passes of ith axle load group during the design period.
Example Let number of load repetition expected by 80 KN standard axle is 1000, 160
KN is 100 and 40 KN is 10000. Find the equivalent axle load. Solution:
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IRC method of design of flexible pavements
Design traffic
The method considers traffic in terms of the cumulative number of standard
axles (8160 kg) to be carried by the pavement during the design life. This requires the
following information:
1. Initial traffic in terms of CVPD
2. Traffic growth rate during the design life
3. Design life in number of years
4. Vehicle damage factor (VDF)
5. Distribution of commercial traffic over the carriage way.
Initial traffic
Initial traffic is determined in terms of commercial vehicles per day (CVPD). For
the structural design of the pavement only commercial vehicles are considered assuming
laden weight of three tones or more and their axle loading will be considered. Estimate of
the initial daily average traffic flow for any road should normally be based on 7-day 24-
hour classified traffic counts (ADT). In case of new roads, traffic estimates can be made
on the basis of potential land use and traffic on existing routes in the area.
Traffic growth rate
Traffic growth rates can be estimated
(i) by studying the past trends of traffic growth, and
(ii) By establishing econometric models. If adequate data is not available, it
is recommended that an average annual growth rate of 7.5 percent may be
adopted.
Design life
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For the purpose of the pavement design, the design life is defined in terms of the
cumulative number of standard axles that can be carried before strengthening of the
pavement is necessary. It is recommended that pavements for arterial roads like NH, SH
should be designed for a life of 15 years, EH and urban roads for 20 years and
other categories of roads for 10 to 15 years.
Vehicle Damage Factor
The vehicle damage factor (VDF) is a multiplier for converting the number of
commercial vehicles of different axle loads and axle configurations to the number of
standard axle-load repetitions. It is defined as equivalent number of standard axles per
commercial vehicle. The VDF varies with the axle configuration, axle loading, terrain,
type of road, and from region to region. The axle load equivalency factors are used to
convert different axle load repetitions into equivalent standard axle load repetitions. For
these equivalency factors refer IRC: 37 2001. The exact VDF values are arrived after
extensive field surveys.
Vehicle distribution
A realistic assessment of distribution of commercial traffic by direction and by lane is
necessary as it directly affects the total equivalent standard axle load application used in
the design. Until reliable data is available, the following distribution may be assumed.
Single lane roads: Traffic tends to be more channelized on single roads than two
lane roads and to allow for this concentration of wheel load repetitions, the design
should be based on total number of commercial vehicles in both directions
Two-lane single carriageway roads: The design should be based on 75 % of the
commercial vehicles in both directions.
Four-lane single carriageway roads: The design should be based on 40 % of the
total number of commercial vehicles in both directions.
Dual carriageway roads: For the design of dual two-lane carriageway roads
should be based on 75 % of the number of commercial vehicles in each direction.
For dual three-lane carriageway and dual four-lane carriageway the distribution
factor will be 60 % and 45 % respectively.
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Numerical example
Design the pavement for construction of a new bypass with the following data:
1. Two lane carriage way
2. Initial traffic in the year of completion of construction = 400 CVPD (sum of
both directions)
3. Traffic growth rate = 7.5 %
4. Design life = 15 years
5. Vehicle damage factor based on axle load survey = 2.5 standard axle per
commercial vehicle
6. Design CBR of subgrade soil = 4%.
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Rigid pavement design
Wheel load stresses - Westergaard's stress equation
The cement concrete slab is assumed to be homogeneous and to have uniform elastic
properties with vertical sub-grade reaction being proportional to the deflection.
Westergaard developed relationships for the stress at
interior, edge and corner regions, denoted as _i; _e; _c in kg/cm2 respectively and
given by the equation.
where h is the slab thickness in cm, P is the wheel load in kg, a is the radius of the wheel
load distribution in cm, l the radius of the relative stiffness in cm 29.1 and b is the radius
of the resisting section in cm
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Temperature stresses
Temperature stresses are developed in cement concrete pavement due to variation
in slab temperature. This is caused by (i) daily variation resulting in a temperature
gradient across the thickness of the slab and (ii) seasonal variation resulting in overall
change in the slab temperature. The former results in warping stresses and the later in
frictional stresses.
Warping stress
The warping stress at the interior, edge and corner regions, denoted as ά ti; ά te; ά tc in kg/cm2 respectively and given by the equation
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Frictional stresses
The frictional stress ά f in kg/cm2 is given by the equation
Where W is the unit weight of concrete in kg/cm2 (2400), f is the coefficient of sub
grade friction (1.5) and L is the length of the slab in meters.
Combination of stresses
The cumulative effect of the different stress give rise to the following thee critical cases
Summer, mid-day: The critical stress is for edge region given by α critical = α e + α te – αf
Winter, mid-day: The critical combination of stress is for the edge region given by α critical = α e+ α te + α f
Mid-nights: The critical combination of stress is for the corner region given by α critical = α c + α tc
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UNIT 7 HIGHWAY CONSTRUCTION
Introduction
The science of highway engineering raises some fundamental questions as to what
is a road or highway, how is it planned and designed and lastly how is it built. By now in
the preceding chapters, Depending upon the desired strength of the pavement, the
aggregate gradations and the type and proportion of binders are decided. These three
basic binder medium give rise to a number of construction methods.
Types of Highway Construction
The highway types are classified as below:
(i) Earth road and gravel roads
(ii) Soil stabilized roads
(iii) Water bound macadam (WBM) road
(iv) Bituminous or black-top roads
(v) Cement concrete roads
The roads in India are classified based on location and functions. All the roads do not
cater for the same amount of traffic volume or intensity. Since the funds available at hand
for financing the construction projects are also meager, it is necessary to have roads which
cost less. The adoption of low cost roads is now preferred in developing countries like
India where large lengths of roads are to be constructed in the rural areas with the limited
finances available in the country. Earth roads and stabilized roads are typical examples of
low cost roads. Stabilized soil roads are gaining importance in the form of low cost roads.
EARTHWORK
General
The subgrade soil is prepared by bringing is to the desired grade and camber and
by compacting adequately. The subgrade may be either in embankment or in excavation,
depending on the topography and the finalized vertical alignment of the road to be
constructed.
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Excavation
Excavation is the process of cutting or loosening and removing earth including rock form
its original position. Transporting and dumping it as a fill or spoil bank. The excavation
or cutting mat is needed in soil, soft rock or even in hard rock, before preparing the
subgrade.
Embankment
When it is required to raise the grade line of a highway above the existing ground
level it becomes necessary to construct embankments. The grade line may be raised due
to any of the following reasons
i) To keep the subgrade above the high ground water table.
ii) To prevent damage to pavement due to surface water and capillary water.
iii) To maintain the design standards of the highway with respect to the Vertical
alignment.
The design elements in highway embankments are:
i) Height
ii) Fill material
iii) Settlement
iv) Stability of foundation, and
Stability of slopes
Height
The height of the embankment depends on the desired grade line of the highway and the
soil profile or topography. Also the height of the fill is some times governed by stability
of foundation, particularly when the foundation soil is weak.
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Fill Material
Granular soil is generally preferred as highway embankment material. Silts, and
clays are considered less desirable. Organic soils, particularly peat are unsuitable. The
best of the soils available locally is often selected with a view to keep the lead and lift as
low as possible. At times light-weight fill material like cinder may be used to reduce the
weight when foundation soil is weak.
Settlement
The embankment may settle after the completion of construction either due to
consolidation and settlement of the foundation or due to settlement of the fill or due to
both. If the embankment foundation consists of compressible soil with high moisture
content, the consolidation can occur due to increase in the load. The settlement of the fill
is generally due to inadequate compaction during construction and hence by proper
compaction this type of settlement may be almost eliminated. Whatever be the type of
settlement, it is desirable that the settlement is almost complete before the construction of
pavement.
Stability of Foundation
When the embankment foundation consists of weak soil just beneath or at a certain
depth below in the form of a weak stratum, it is essential to consider the stability of the
foundation against a failure. This is all the more essential in the case of high
embankments. The foundation stability is evaluated and the factor of safety is estimated
by any of the following approaches:
(b) Estimating the average shear stress and strength at the foundation layers by
approximate methods and estimating the factor of safety.
(c) Using theoretical analysis based on elastic theory.
The factor of safety in the case of compressible soil foundation is likely to be
minimum just after the completion of the embankment. Later due to consolidation of
foundation and consequent gain in strength there will be an increase in the foundation
factor of safety.
Stability of Slopes
The embankment slopes should be stable enough to eliminate the possibility of a
failure under adverse moisture and other conditions. Hence the stability of the slope
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should be checked or the slope should be designed providing minimum factor of safety of
1.5. Often much flatter slopes are preferred in highway embankments due to aesthetic and
other reasons.
Construction of embankments
The embankment may be constructed either by rolling in relatively thin layers or
by hydraulic fills. The former is called rolled-earth method and is preferred in highway
embankments. Each layer is compacted by rolling to a satisfactory degree or to a desired
density before the next layer is placed.
Preparation of Subgrade
The preparation of subgrade includes all operations before the pavement structure
could be laid over it and compacted. Thus the preparation of subgrade would include site
clearance, grading (embankment or cut section) and compaction. The subgrade may be
situated on embankment or excavation or at the existing ground surface. In all the cases,
site should be cleared off and the top soil consisting of grass roots rubbish and other
organic matter are to be removed. Next, the grading operation is started so as to bring the
vertical profile of the subgrade to designed grade and camber. Bull dozers, scrapers and
blade graders are useful equipment to speed up this work. It is most essential to compact
the top of
Soil Compaction
By compaction of soil, the particles are mechanically constrained to be packed
more closely, by expelling part of the air voids. Compaction increases the density and
stability, reduces settlement and lowers the adverse effects of moisture. Hence proper
compaction of fills, subgrade, sub-base and base course are considered essential for
proper highway construction.
The various factors influencing soil compaction include the moisture content, amount and
type of compaction, soil type and stone content. It is a well known fact that there is an
optimum moisture content (OMC) for a soil which would give maximum dry density for
a particular type and amount of compaction. Hence it is always desirable to compact the
soil at the OMC after deciding the compacting equipment.
Compacting equipment
Soil compaction is achieved in the field either by rolling, ramming or by vibration.
Hence the compacting equipment may also be classified as rollers, rammers and vibrators.
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Compactions of sands are also achieved by watering ponding and jetting.
Rollers
The principle of rollers is the application of pressure, which is slowly increased
and then decreased. The various type of rollers which are used for compaction are smooth
wheel, pneumatic tyred and sheep foot rollers. Further the construction equipment such as
trucks, tractors and bull dozers also help in compaction of the materials to some extent.
CONSTRUCTION OF EARTH ROADS
General
An earth road is the cheapest type of road prepared from natural soil. The pavement
sections is totally made out of the soil available at site and at near-by borrow pits. The
type of construction by and large, depends upon the type of soil at site.
keep the pavement surface free of standing water; otherwise the soil being Previous, the
water would damage the pavement section by softening it. The maximum cross slope of 1
in 20 is recommended to avoid erosion due to rain waters and formation of cross ruts.
Specification of Materials
Soil of the following properties is considered satisfactory for constructing earth roads:
Base Course Wearing course
Clay content < 5% 10 to 18%
Silt content 9 to 32% 5 to 15%
Sand Content 60 to 80% 60 to 80%
Liquid limit <35% <35%
Plasticity index <6% 40 to 10%
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Construction Procedure
The construction of earth road may be divided into the following steps:
Material. The soil survey is carried out and suitable borrow pits are located within
economical haulage distances. The borrow pits are usually selected outside the land
width. The trees, shrubs, grass roots and other organic matter including top soil a
removed before excavating earth for construction.
Location. The centre line and road edges are marked on the ground along the
alignment, by driving wooden pegs. Reference pegs are also driven to help in
following the desired vertical profile of the road during construction. The spacing of
the reference pegs depends on the estimated length of road construction per day
c) Shaping of subgrade.
The site clearance may be carried out manually using appliances like spade, pick and
shovel. Mechanical equipment like dozer, scraper and ripper may also be used for the
purpose. Construction of fills and excavation of costs to bring the road profile to the
desired grade may also be done either manually or using excavation, hauling and
compaction equipment.
Pavement construction. The borrowed soil (more than one soil type mixed to the
desired proportion, if necessary) is dumped on the prepared subgrad and pulverized. The
field moisture content is checked and additional water is added, if necessary, to bring it
upto OMC. light compaction is considered desirable. The camber of the finished
pavement surface is checked and corrected if necessary.
Opening to traffic. The compacted earth road is allowed to dry out for a few days
before opening to traffic.
CONSTRUCTION OF GRAVEL ROADS
General
Gravel roads are considered superior to earth roads as they can carry heavier
traffic. The road consists of a carriageway constructed using the gravels. The camber mat
be between I in 25 and 1 in 30. A well compacted crushed rock or gravel road is fairly
resilient and does not become slippery when wet.
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Material
Hard variety of crushed stone or gravel of specified gradation is uses. However
Varieties of Stone may also be utilized. There are no specifications for the mal Rounded
stones and river gravel are not preferable as there is poor interlocking.
Construction Procedure
Material Gravel to be used for the construction is stacked along the sides of theproposed
road.
Preparation of subgrade. Site is cleared and fills and cuts are completed. Trench
isformed to the desired depth of construction. The width of the trench is made equal to
that of the carriageway. The trench is brought to the desired grade and is compacted.
Pavement construction. Crushed gravel aggregates are placed carefully in the trenchso
as to avoid segregations. Aggregates are spread with greater thickness at centre and less
towards the edges so as to obtain the desired camber. The layer is rolled using smooth
wheeled rollers starting from the edges and proceeding towards the centre with an
overlap of atleast half the width of roller in the longitudinal direction. Some quantity of
water may also be sprayed and rolling is done again s that the compaction is effective.
The camber is checked and corrected from time to time using a template or camber
board.
Opening to traffic. A few days after the final rolling and drying out, the road
isopened to the traffic.
CONSTRUCTION OF WATER BOUND MACADAM ROADS
General
The Water bound macadam (WBM) is the construction known after the name of
John also article 2.16 and 2.17. The term macadam in the present day means, the
pavement base course made of crushed or broken aggregate mechanically interlocked by
rolling and the voids filled with screening and binding material with the assistance of
water.
Specifications of Materials for WBM Pavement
Coarse Aggregates
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The coarse aggregate used in WBM generally consists of hard varieties of crushed
aggregates or broken stones. However, soft aggregates like over burnt bricks metal or
naturally occurring soft aggregates such as kankar or laterite may be used. Crushed slag
obtained from blast furnace may also be used
Property Requirements for Pavement layer
Sub-base Base Course Surfacing course
(i) Los Angeles abrasion 60 50 40
(maximum value, percent)
or
(ii) Aggregate impact 50 40 30
(maximum value, percent)
(iii) Flakiness index - 15 15
(maximum value, percent)
Properties of Coarse Aggregates
The crushed stone aggregate should be generally hard, durable and free from
flaky and elongated particles. The IRC specifies the following ph requirement of
coarse aggregates for WBM construction, in terms of the test value the three
pavement layers.
Size and Grading Requirements of Coarse Aggregates
The coarse aggregates for each layer of construction should, as far as
possible conform to any one of the three gradings specified below. Grading No.1.
consists of Coarse aggregates of size range 90 to 40 mm and is more suitable for
sub-base course. Thickness of compacted layer is usually 100 mm. Grading No. 2
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consists of aggregates size range 63 to 40 mm and grading No. 3 of range 50 to 20
mm and compacted thickness of each layer is normally 75 mm..
Binding material consisting of fine grained material is used in WBM construction
to prevent raveling of the stones Kankar nodules or lime stone dust may also be utilized,
if locally available. The binding material with plasticity index value 4 to 9% is used in
WBM surface course construction; the plasticity index of binding course material should
be less than 6.0% in the case of WBM layers used as base course or sub-base course, with
bituminous surfacing. If the screenings used consist of crushable material like moorum or
soft gravel, there is no need to apply binding material, unless the plasticity index value is
low.
Quantity of Materials
The approximate loose quantities of materials required in m3 for 10 cm compacted
thickness of WBM sub-base using coarse aggregate of grading no I per 10 m2 area
are:
(a) Coarse aggregate size 90 to 40 mm = 1.21 to 1.43
(b) Stone screening type A, 12.5 mm size = 0.40 to 0.44
or
Crushable type screenings (moorum/gravel) = 0.44 to 0.47
(c) Binding material for sub-base course = 0.88 to 0.10
The approximate loose quantities of materials required in m3 for 7.5 cm compacted
thickness of WBM base course or surfacing course using coarse aggregate of
grading No. 2 per 10 m2 area are:
(a) Coarse aggregate size 63 to 40mm = 0.91 to 1.07
(b) Stone screening type A, 12.5 mm size for base course = 0.18 to 0.21
Stone screenings for surfacing course = 0.15 to 0.17
Alternatively, Stone screenings type B,
9.0 mm size for base course = 0.30 to 0.33
9.0 mm size for surfacing = 0.24 to 0.26
Alternatively, crushable type screenings = 0.33 to 0.35
(c) Binding material for base course = 0.06 to 0.09
Binding material for surfacing course = 0.10 to 0.15
(Note: Binding material is not required if crushable type of screening is used).
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Construction Procedure
Preparation of Foundation for Receiving the WBM course
The foundation for receiving the new layer of WBM may be either the subgrade or
sub-base or base course. This foundation layer is prepared to the required grade and
camber and the dust and either loose materials are cleaned. On existing road surface, the
depressions and pot-holes are filled and the corrugations are removed by scarifying and
reshaping the surface to the required grade and camber as necessary. If the existing
surface is a bituminous surfacing, ftirrows of depth 50 mm and width 50 mm cut at 1.0 m
intervals and at 45 degrees to the centre line of the carriageway before laying the Coarse
aggregate.
Provision of Lateral confinement
Lateral confinement is to be provided before starting WBM construction. This may
be done by constructing the shoulders to advance, to a thickness equal to that of the
compacted WBM layer and by trimming the inner sides vertically
Spreading of Coarse Aggregates
The coarse aggregates are spread uniformly to proper profile to even thickness
upon the prepared foundation and checked by templates. The WBM course is normally
constructed to compacted thickness of 7.5 cm except in the case of WBM sub-base course
using coarse aggregate grading no.1 which is of 10.0 cm compacted thickness.
Rolling
After spreading the coarse aggregates properly, compaction is done by a three
wheeled power roller of capacity 6 to 10 tons or alternatively by an equivalent vibratory
roI1q the weight of the roller depends on the type of coarse aggregates.
Application of Screenings.
After the coarse aggregates are rolled adequately, the dry screenings are
gradually over the surface to fill the interstices in three or more applications
Sprinkling and Grouting
After the application of screenings, the surface is sprinkled with water, swept
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rolled. Wet screenings are swept into the voids using hand brooms. Ad• screenings are applied and rolled till the coarse aggregates are well bonded and firmly set.
Application of Binding Material
After the application of screening and rolling, binding material is applied at a
uniform and slow rate at two or more successive thin layers. After each application of
binding material, the surface is copiously sprinkled with water and wet slurry swept with
brooms to fill the voids.
Setting and Drying
After final compaction, the WBM course is allowed to set over-night. On the next
day the „hungry‟ spots are located and are filled with screenings or binding material,
lightly sprinkled with water if necessary and rolled. No traffic is allowed till the WBM
layer sets and dries out.
Checking of Surface Evenness and Rectification of Defects
The surface evenness of longitudinal direction is checked by 3.0 m straight edge
and the number of undulations exceeding 12mm in the case if WBM layer of grading no.
1 and 10mm in the case of grading nos. 2 and 3 are recorded in each completed length of
300m; the maximum number of undulations permitted in each case in 30. The spots with
15mm undulations are marked for rectification of defects.
CONSTRUCTION OF BITUMINOUS PAVEMENTS
Introduction
Bituminous pavements are in common use in India and abroad. It is Possible
to construct relatively thin bituminous pavement layers over an existing Pavement
stages by constructing bituminous pavement layers one after another in a certain period of
time unlike the cement concrete pavement construction
Types of Bituminous Construction
Number of types and methods are in use for bituminous pavement construction. It
is attempted to broadly classify them here based on the methods of construction. The
following construction techniques are in use:
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Interface treatment like prime coat and tack
coat Surface dressing and seal coat
Grounted or penetration type constructions :
a) Penetration macadam b) Built-up spray Grout.
Premix which may be any of the following:
a) Bituminous bound macadam b) Carpet c) Bituminous concrete d) Sheet asphalt or rolled asphalt e) Mastic asphalt
Explanatory Notes on Bituminous Construction Types
Interface Treatment
Thus surface of the existing pavement layer is to be cleaned to remove dust and dir
and a thin layer of bituminous binder is to be sprayed 1.
Prime coat: Bituminous prime coat is the first application of a low viscosity
liquidbituminous material over an existing porous or absorbent pavement surface like the
WBM base course.
Tack coat. Bituminous tack coat is the application of bituminous material over existing
pavement surface which is relatively impervious like an existing bituminous surface or a
cement concrete pavement or a pervious surface like the WBM which has already been
treated by a prime coat.
Bituminous Surface Dressing
Bituminous Surface Dressing (BSD) is provided over an existing pavement to
serve as thin wearing coat. The single coat surface dressing consists of a single
application of bituminous binder material followed by spreading of aggregate cover and
rolling. When the surface dressing is similarly done in two layers, it is called „two coat
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bituminous surface dressing‟.
Seal Coat
Seal coat is usually recommended as a top coat over certain bituminous
pavements which are not impervious, such as open graded bituminous constructions like
premixed carpet and grouted Macadam. Seal coat is also provided over an existing
bituminous pavement which is worn out.:
(a) To seal the surfacing against the ingress of water
(b) To develop skid resistant texture
(c) To enliven an existing dry or weathered bituminous surface.
Penetration Macadam
Bituminous Penetration Macadam or Grouted Macadam is used as a base or binder
course. The coarse aggregates are first spread and compacted well in dry state and
after that hot bituminous binder of relatively high viscosity is sprayed in fairly large
quantity at the top
Premix Methods
In this group of methods the aggregates and the bituminous binder are mixed
thoroughly before spreading and compacting. It is possible to coat each particle of
aggregate with the binder still the quantity of binder used may be considerably lesser than
penetration macadam type construction. In premixed constructions, the quantity of
bitumen used could be precisely controlled and they offer increased stability of the mix
even with lower bitumen contents.
Bituminous Macadam
Bituminous Macadam (BM) or Bitumen Bound Macadam is a premixed
construction method consisting of one or more courses of compacted crushed aggregates
premixed with bituminous binder, laid immediately after mixing. The BM is laid in
compact thicknesses of 75 mm or 50 mm and three different gradations of aggregates
have been suggested for each thickness to provide open graded and semi-dense
constructions.
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Bituminous Premixed Carpet
Premixed Carpet (PC) consists of coarse aggregates of 12.5 and 10.0 mm sizes,
premixed with bitumen or tar binder are compacted to a thickness of 20 mm to serve as a
surface course of the pavement. Being a open graded construction, the PC is to be
invariably covered by a suitable seal coat such as premixed sand-bitumen seal coat before
opening to traffic. The PC consists of all aggregates passing 20 mm and retained on
6.3mm sieve. When a fairly well graded material as per specification is used for the
construction of the bituminous carpet of thickness 20 o 25 mm, the construction method
is called semi-dense carpet.
Bituminous Concrete or Asphalt Concrete
Bituminous Concrete or Asphaltic Concrete (AC) is a dense graded premixed
bituminous mix which is well compacted to form a high quality pavement surface Course.
The AC consists of a carefully proportioned mixture of coarse aggregates fine aggregates,
mineral filler and bitumen and the mix is designed by an appropriate method such as the
Marshall method to fulfil the requirements of stability, density, flexibility and voids. The
thickness of bituminous concrete surface course layer usually ranges from 40 to 75 mm.
The IRC has provided specification for 40 mm thick AC surface course for highway
pavements.
Sheet Asphalt
Sheet asphalt or rolled asphalt is a dense sand-bitumen premix of compacted
thickness 25 mm, used as a wearing course. The sheet asphalt consists of well graded
coarse to fine sand (without coarse aggregates) and a suitable penetration grade bitumen
to from a dense and impervious layer. This is usually laid over cement concrete pavement
to provide an excellent riding surface. The sheet asphalt also protects the joints in cement
concrete pavements and could cause a reduction in warping stresses due to a decrease in
the temperature variations between top and bottom of the concrete slab.
Mastic Asphalt
Mastic asphalt is a mixture of bitumen, fine aggregates and filler in suitable
proportions which yields a voidless and impermeable mass. Though the ingredients in
mastic asphalt are similar to those in bituminous concrete, properties of mastic asphalts
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are quite different. The mastic asphalts when cooled results in a hard, stable and durable
layer suitable to withstand heavy traffic. This material also can absorb vibrations and has
property f self-healing of cracks without bleeding. It is a suitable surfacing materials for
bridge deck slabs.
Construction Procedure for Bituminous Macadam
The Bituminous Macadam (BM) bitumen bound macadam is a premix laid
immediately after mixing and then compacted. It is an open graded construction suitable
only as a base or binder course. When this layer is exposed as a surface course, at least a
seal coat is necessary.
Specifications of Materials:
The grades of bitumen used are 30/40, 60/70 and 80/100 penetration. Road tar RT-
4, cutback and emulsion can also be used in cold mix construction technique. The binder
content used varies from 3.0 to 4.5 percent by weight of the mix). Aggregates used are of
low porosity fulfilling the following requirements for the base Course.
Los Angle abrasion value 50 percent max.
Aggregate impact value 35 percent max.
Flakiness index 15 percent max.
Stripping at 40°C after 24 hours immersion (CRRI test) 25 percent max.
Loss with sodium sulphate, 5 cycles 12 percent max.
For binder course the specified maximum abrasion and impact values are 40 and
30 percent respectively.
The grading of the aggregates for 75 mm and 50 mm thickness for base and binder
course instruction as specified by Indian Roads Congress are given in Table 8.4 (a) &
respectively. The quantity of aggregates required for 10 m2 of bitumen bound macadam
are 0.60 to 0.75 m3 and 0.90 to 1.0 m3 respectively, for 50 and 75 mm compacted
thickness. The bitumen quantity would be determined based on the grading adopted as
specified above.
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Constructions Steps
Preparation of existing layer: The existing layer is prepared to a proper profile. Pot
holes are patched and irregularities are made even. The surface is properly cleaned.
Tack coat or prime coat application: A track coat is applied of thin layer of bitumen
binder on the existing layer either using the sprayer or a pouring can. the quantity of
application is 40 to 7.5 kg per 10 m2 for black top layer and 7.5 to 10kg per 10 m2 for
untreated WBM layer.
Premix preparation: The bitumen binder and aggregates as per recommended
gradingsare separately heated to the specified temperatures and are then placed in the
mixer
chosen for the job. The mixing temperature for each grading and the bitumen binder is
also specified based on. the laboratory results. A tolerance of ± 10°C is allowed. The
mixing is done till a homogeneous mixture is obtained. The mixture is then carried to
the site for its placement through a transporter or a wheel barrow.
Placement. The bituminous paving mixture is then immediately placed on the
desiredlocation and is spread with rakes to a pre-determined thickness. The camber
profile is checked with a template. It may be stated here that a compacting
temperature also influences the strength characteristic of the resulting pavement
structure. It is therefore required that the minimum time is spent between the
placement of the mix and the rolling operations.
Rolling and finishing The paving mix. The rolling is done with 8 to 10 tones
tandemroller. The rolling is commenced from the edges of the pavement construction
towards the centre, and uniform overlapping is provided. The finished surface should
not show separate lines of markings due to defective or improper rolling. The roller
wheels are kept damp, otherwise the paving mix may partly stick to the wheels and the
finishing may not be good. A variation of 6 mm over 3 m length is allowed in the
cross profile. The number of undulations exceeding 10 nun should be less than 30 in
300 m length of pavement.
Construction Procedure for Bituminous Concrete
The bituminous concrete is the highest quality of construction in the group of
black top surface. Being of high cost specifications, the bituminous mixes are properly
designed to satisfy the design requirements of the stability and durabi1ity. The mixture
contains dense grading of coarse aggregate, fine aggregate and mineral filler coated with
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bitumen binder. The mix is prepared in a hot-mix plant. The thickness of the bituminous
concrete layer depends upon the traffic and quality of base course.
The specifications of materials and the construction steps for bituminous concrete or
asphaltic concrete (AC) surface course are given below:
Specification of Materials:
a) Binder: Bitumen of grade 3 0/40,60/70 or 80/100 may be chosen depending Upon
tic
b) Aggregates and Filler: The coarse aggregates should fulfill the following
requirements
Aggregate impact value, maximum percent : 30
or Loss Angeles abrasion value, max percent : 40
Flakiness index, max percent : 25
Stripping at 40°C after 24 hours, max percent : 25
Soundness:
Loss with sodium sulphate in 5 cycles, max. percent : 12
Loss with magnesium sulphate in 5 cycles, max. percent : 18
The gradation of aggregates and filler should conform to those given in Table 8.5.
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Table 8.5 Gradation of Aggregates for Bituminous Concrete
Sieve Size, mm Percent passing by
weight
Grading 1 Grading 2
20.00 - 100
12.50 100 80-100
10.00 80-100 70-90
4.75 55-75 50-70
2.36 35-50 35-50
0.60 18-29 18-29
0.30 13-23 13-23
0.15 8-16 8-16
0.75 4-10 4-10
CONSTRUCTION OF CEMENT CONCRETE PAVEMENTS
Introduction
The Cement concrete pavement maintains a very high recognition among the
engineer and the road users alike. Due to the excellent riding surface and pleasing
appearance, the cement concrete roads are very much preferred.
Specifications of material for cement concrete pavement slabs.
The materials required for plain concrete slabs are cement coarse aggregates, fine
aggregates and water. In case reinforcement is provided, steel wire fabric or bar mats may
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be used of the required size and spacing. Other materials are for the construction of joints,
such as load transfer devices, joints filler and sealer.
Cement:
Ordinary portland cement is generally used. In case of urgency rapid hardening
cement may also be used to reduce curing time.
Coarse aggregates:
The maximum size of coarse aggregates should not exceed one fourth the slab
thickness. The gradation of coarse aggregate may range from 50 to 4.75 mm or 40 to 4.75
mm, the aggregate is collected in two size ranges, one below and the other above 20mm
size. When the grading is from 20 to 50 mm, the materials are collected in two groups,
below and above 25 mm size.:
Fine aggregate.
Natural sands should be preferred as fine aggregate though crushed Stones may
also be used.
Proportioning of concrete.
The concrete may be proportioned so as to obtain a minimum modulus of rupture
of 40 kg/cm2 on field specimens after 28 days curing or to develop a minimum
compressive strength of 280 kg/cm2 at 28 days, or higher value as desired in the design.
Plants and Equipment
The equipment necessary for the construction of cement concrete slabs are for
batching, placing, finishing and carrying the concrete pavement. Equipment commonly
used are given below.
Concrete Mixer:
If batching by volume is required then the separate measuring boxes are provided
for the different aggregates. Each box is provided with a straight edge for striking off
excess material after filling.
Batching Device
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Concrete mixer of adequate capacity of the batch type is provided. It has a rated
capacity of not less than 0.2 m3 of mixed concrete. The mixture is equipped with a water
measuring device capable of accurate measurement of water required per batch. Some
mixtures are also equipped with timing devices which automatically lock the discharge
lever during the full time of mixing and releases it at the end of mixing period.
Wheel Borrow
Wheel borrows with two wheels are used to transport concrete for short distances
from the mixer.
Vibrating Screed
Vibrating screed comprises of a wooden or mild steel screed with suitable handles
driven by vibrating units mounted thereon, propelled either electrically or by compressed
air or by a petrol engine, and travelling on side forms.
Internal Vibrators
It comprises of vibrating head with suitable motive power either of compressed air,
electricity or of a petrol driven engine right enough to ensure proper control and
manipulation in the mass of concrete. It is used to ensure compaction of the cement
concretealong with the forms and also to avoid any tendency of honey-combing at the
edges of the slab.
Tools and appliances for surface, finishing operations in common use are float,
straight edge, belt and fiber brush.
Float
The longitudinal float is of 75 cm length and 7.5 cm width and is made of hard
wood and is fixed with handle. (See Fig. 8.15). This is used for smoothing the concrete.
Straight Edge:
It is used to check the finished pavement surface in longitudinal direction. It is
made of hard wood with M.S. plate at bottom, 3 meter in length, 10 cm in width with two
handles as shown in Fig. 8.16.
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Belt:
Canvas belts are used for finishing the pavements surface before the concrete
hardens. The canvas is of 25 cm width and atleast 75 cm longer than the width of
pavement slab. It has two wooden handles at the end. See Fig. 8.17.
Fibre Brush:
Fibre brush broom is used to make broom marks across the pavement surface and
to make it skid resistance. Hard fibres are used projecting out of the wooden bursh of
length 45cm and width 7.5 cm, with a handle about 2 meter long.
Edging Tool
The edging tool is used for rounding the transverse edges at expansion joints and
the longitudinal edges. The vertical limb of this tool extends to the required depth. The
rounded edge of the M.S. plate has radius f 6 mm.
Other Small Tools
Other small tools d equipment such as spades, shovels and pans water pots etc.
necessary for the work are also provided.
Construction steps for cement concrete pavement slab
(i) Preparation of Subgrade and Sub-base
The subgrade or sub-base for laying of the concrete slabs should comply with the
wing requirement; that no soft spots are present in the subgrade or sub-base; that the
uniformly compacted subgrade or sub-base extends atleast 30 cm on either side of the
width to be concreted; that the subgrade is properly drained; that the minimum modulus
subgrade reaction obtained with a plate bearing test is 5.54 kg/cm2.
over the soil subgrade. In such a case, the moistening of the subgrade prior to
placing of the concrete is not required.
(iii) Batching of Material and Mixing
After determining the proportion of ingredients for the field mix, the fine
aggregates and coarse aggregates are proportioned by weight in a weight-batching plant
and placed into the hopper along with the necessary quantity of cement. Cement is
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measured by the bag. All batching of material is done on the basis of one or more whole
bags of cement.
(iv) Transporting and Placing of Concrete
The cement concrete is mixed in quantities required for immediate use and is
deposited on the soil subgrade or sub-base to the required depth and width of the
pavement section within the form work in continuous operation.
(v) Compaction and Finishing
The surface of pavement is compacted either by means of a power-driven finishing
machine or by a vibrating hand screed. For areas where the width of the slab is
very small as at the corner of road junctions, etc., hand consolidation and finishing
may be adopted:
(a) Concrete as soon as placed, is struck off uniformly and screeded to the
crown and cross-section of the pavement to conform the grade.
(b) The tamper is placed on the side forms and is drawn ahead in combination
with a series of lifts and drops to compact the concrete.
Floating and Straight Edging
The concrete is further compacted by means of the longitudinal float. The
longitudinal float is held in a position parallel to carriageway centre line and passed
gradually from one side of the pavement to the other. After the longitudinal floating is
done and the excess water gets disappeared, the slab surface is tested for its grade and
level with the straight edge.
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HIGHWAY DRAINAGE
INTRODUCTION
Highway drainage is the process of removing and controlling excess surface and
sub-soil water within the right of way this includes interception and diversion of water
from the road surface and subgrade. The installation of suitable surface and sub-surface
drainage system is an essential part of highway design and construction.
IMPORTANCE OF HIGHWAY DRAINAGE
Significance of Drainage
An increase in moisture content causes decrease in strength or stability of a soil
mass the variation in soil strength with moisture content also depends on the soil type and
the mode of stress application. Highway drainage is important because of the following
reasons:-
Excess moisture in soil subgrade causes considerable lowering of its stability the
pavement is likely to fail due to subgrade failure as discussed in Article 10.1.
Increase in moisture cause reduction in strength of many pavement materials like
stabilized soil and water bound macadam.
In some clayey soils variation in moisture content causes considerable variation in
flume of subgrade. This sometimes contributes to pavement failure.
One of the most important causes of pavement failure by the formation of waves and
corrugations in flexible pavements is due to poor drainage.
Sustained contact of water with bituminous pavements causes failures due to stripping
of bitumen from aggregates like loosening or detachment of some of the bituminous
pavement layers and formation of pot holes.
In places where freezing temperatures are prevalent in winter, the presence of water in
the subgrade and a continuous supply of water from the ground water can cause
considerable damage to the pavement due in frost action.
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Requirements of Highway Drainage System
The surface water from the carriageway and shoulder should effectively be drained off
without allowing it to percolate to subgrade.
The surface water from the adjoining land should be prevented from entering the
roadway. The side drain should have sufficient capacity and longitudinal slope to carry
away all the
surface water collected.
Flow of surface water across the road and shoulders and along slopes should not cause
formation of cress ruts or erosion.
SURFACE DRAINAGE
The surface water is to be collected and then disposed off. The water is first
collected in longitudinal drains, generally in side drains and then the water is disposed off
at the nearest stream, valley or water course. Cross drainage structures like culverts and
small bridges may be necessary for the disposal of surface water from the road side
drains.
Collection of Surface Water
The water from the pavement surface is removed by providing the camber or cross
slope to the pavement. The rate of this cross slope is decided based on type of pavement
surface and amount rainfall.
where there is restriction of space, Construction of deep open drains may be undesirable.
This is particularly true when the road formation is in cutting. In such cases covered
drains or drainage trenches properly filled with layers of coarse sand and gravel may be
used. In urban roads because of the limitation of land width and also due to the presence
of foot path, dividing islands and other road facilities, it is necessary to provide
underground longitudinal
drains. Water drained from the pavement surface can be carried forward in the longitudinal
direction between the kerb and the pavement for short distances (See Fig. 4.9). This water
may be collected in catch pits at suitable intervals and lead through underground drainage
pipes. Section of a typical catch pit with grating to prevent the entry of rubbish into the
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drainage system.
Drainage of surface water is all the more important in hill roads. Apart from the
drainage of water from the road formation, the efficient diversion and disposal of water
flowing down the hill slope across the road and that from numerous cross streams is an
important part of hill road construction. If the drainage system in hill road is not adequate
and efficient, it will result in complex maintenance problems.
Design of Surface Drainage System
The design of surface drainage system may be divided into two phases:
(i) Hydrologic analysis
(ii) Hydraulic analysis
Once the design runoff Q is determined, the next step is the hydraulic design
of drains. The side drains and partially filled culverts are designed based on the
principles of flow through open channels.
Data for Drainage Design
The following data are to be collected for the design of road side drain:
Total road length and width of land from where water is expected to flow on the stretch
of the side drain.
Run-off coefficients of different types of surfaces in the drainage area and their respective
areas (such as paved area, road shoulder area, turf surface, etc.)
Designed Steps
Simplified steps for the design of longitudinal drains of a road to drain off the
surface water given below:
The frequency of return period such as 10 years, 25 years etc. is decided based on
finances available and desired margin of safety, for the design of the drainage system.
The values of coefficients of run-off C1, C2, C3 etc. from drainage areas A1, A2, A3
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etc. are found and the weighted value of C is computed.
Inlet time for the flow of storm water from the farthest point in the drainage area
to the drain inlet along the steepest path of flow is estimated from the distance, slope of
the ground and type of the cover. Figure 11.3 may be used for this purpose.
Time of flow along the longitudinal drain T2 is. determined for the estimated length of
longitudinal drain L upto the nearest cross drainage or a water course and for the
allowable velocity of flow V in the drain i.e., T2 = L.
The total time T for inlet flow and flow along the drain is taken as the time of
concentration or the design value of rain fall duration, T = T1 + T2.
The required depth of flow in the drain is calculated for a convenient bottom width
and side slop of the drain. The actual depth of the open channel drain may be increased
slightly to give a free board. The hydraulic mean radius of flow R is determined.
The required longitudinal slope S of the drain is calculated using Manning‟s formula adopting suitable value of roughness coefficient n.
drain in a sandy clay soil from the inlet point to the cross drainage is 540m. The velocity
of flow in the side drain may be assumed as 0.6 rn/sec so that silting and erosion are
prevented. Estimate the design quantity of flow on the side drain for a ten-years period
of frequency of occurrence of the storm.
Cross Drainage
Whenever streams have to cross the roadway, facility for cross drainage is to be
provided. Also often the water from the side drain is taken across by these cross drain in
order to divert the water away from the road, to a water course or valley. The cross
drainage structures commonly in use are culveris and small bridges. When a small stream
crosses a road with a linear waterway less than about six meter, the cross drainage
structure provided is called culvert; for higher values of linear waterway, the structure is
called a bridge.
SURFACE DRAINAGE
Change in moisture content of subgrade are caused by fluctuations in ground water
table seepage flow, percolation of rain water and movement of capillary water and even
water vapour. In sub-surface drainage of highways, it is attempted to keep the variation of
moisture in subgrade soil to a minimum. However only the gravitational water is drained
by the usual drainage systems.
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Lowering of Water Table
The Highest level of water table should be fairly below the level of subgrade, in
order that the subgrade and pavement layers are not subjected to excessive moisture.
From practical considerations it is suggested that the water table should be kept atleast 1.0
to 1.2 m the subgrade. In places where water table is high (almost at ground level at
times) the best remedy is to take the road formation on embankment of height not less
than 1.0 to 1.2 meter. When the formation is to be at or below the general ground level, it
would be necessary to lower the water table.
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UNIT 8 HIGHWAY ECONOMICS & FINANCE
INTRODUCTION
Better highway system provides varied benefits to the society. Improvements in
highway results in several benefits to the road users such as :Reduction in vehicle
operational cost per unit length of road. saving travel time and resultant benefits in terms
of time cost of vehicles and the passengers Reduction in accident rates. Improved level of
service and ease of driving. Increased comfort to passengers. Therefore he level of service
of a road system may be assessed from the benefits to the users The improvement in road
net work also benefits the land owner by providing better access and consequently
enhancing the land value. The cost of improvements in the highway of land, materials,
construction work and for the other facilities should be worked out. From the point of view
of economic justification for the improvements, the cost reductions to the highway users
and other beneficiaries of the improvements during the estimated period should be higher
than the investments made for the improvement. In the planning and design of highways
there is increasing need for analysis to indicate justification of the expenditure required and
the comparative worth of proposed improvements, particularly when various alternatives
are being compared.
The government or any other agency finances highway developments. The funds for these
are generally recovered 1ins the road users in the form of direct and indirect taxations.
HIGHWAY USER BENEFITS
General Benefits
Several benefits are brought to highway users and others due to the construction of
a new highway or by improving a highway. Road user benefits are the advantages,
privileges or savings that accrue to drivers or owners through the use of one highway
facility as compared with the use of another. The various benefits due to highway
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improvement may be classified into two categories: (i) quantifiable or tangible benefits in
terms of market values and (ii) non quantifiable or intangible benefits.
Quantifilab1e Benefits
Various benefits which can be quantified include benefits to road user such as
reduction in vehicle operation cost, time cost and accident cost. The other benefits
include enhancement in land value. These are briefly explained below:
Saving in vehicle operation cost is due to reduction in fuel and oil consumption and
reduction in wear and tear of tyres and other maintenance costs. A road with sharp
curves and steep grades require frequent speed changes; presence of intersections
require stopping idling and accelerating; vehicle operation on road stretches with high
traffic volume or congestion necessitates speed changes and stopping and increased
travel time.
Non-quantable Benefits
The non-quantifiable benefits due to improvements in highway facilities include
reduction in fatigue and discomfort during travel, increase in comfort and conveniences
and improvement in general amenities, social and educational aspects, development of
recreational and medical services, improved mobility of essential services and defence
forces, aesthetic values, etc..
Motor Vehicle Operation Cost
The factors to be considered for evaluating motor vehicle operation cost would
differ depending on the purpose of the analysis. The vehicle may be classified in
different groups such as passenger cars, buses, light commercial vehicles, single unit
trucks combination vehicles etc., for the purpose of cost analysis. The motor vehicle
operation costs depend on several factors which may be grouped .as given below:
Cost dependent on time expressed as cost per year such as interest on capita
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depreciation cost, registration fee, insurance charges, garage rent, driver‟s license salaries etc. as applicable.
Cost depending on distance driven expressed as cost per vehicle-kilometer. The items
which may be included here are fuel, oil, tyres, maintenance and repairs etc.
Cost dependent on speed include cost of fuel, oil and tyre per vehicle-km-time-cost of
vehicles, travel time value of passengers, etc.
Cost dependent on type of vehicle and its condition. Operation costs of larger vehicles
are comparatively higher. The operation cost of old vehicles maintained in poor
condition is also higher.
Accident costs.
The costs of vehicle operation and time for unit distance may be taken as:
T = a+ (b+c) (14.1)
Speed
Where
a = running cost per unit distance, independent of journey time
b = a fixed hourly cost, dependent on speeds
c = the portion of the running cost which is dependent on speed
pavement surface and its condition, grades, curves and traffic volumes. Also the time
costs and accident costs are taken into consideration.
Example 14.1
Calculate the operating cost of a passenger car for 100 km length of a rural
highway with no sharp curves for most economical speed of vehicles operation using
the following
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HIGHWAY COSTS
General
The total Highway Cost for road user benefit analysis is the sum of the capital
costs expressed on an annual basis and the annual cost of maintenance. The total cost for
highway improvement is obtained from the estimate prepared from the preliminary plans.
The total cost of each highway engineering improvement proposal is calculated from the
following five components
(i) Right of way
(ii) Grading drainage, minor structures
(iii) Major structures like bridges
(iv) Pavement and appurtenances
(v) Annual cost of maintenance and operation
Computation of total annual highway cost based on summation of the annual cost of
individual items of improvements and their average useful lives is considered to be a
proper and accurate approach.It is difficult to estimate the service lives of highway
elements as there are several variables such as soil, climate topography and traffic. Road
life studies enable estimation of lives of pavements, bridges and other roadway facilities.
(i) Administration (a portion) Personal service, building, equipment operation,
office, insurance etc.
(ii) Highway operation Equipment. building vehicle operation including capital
costs of vehicle.
(iii) Highway maintenance
(iv) Highway capital cost : Cost of highway components such as right of way,
damage, earthwork, drainage system. pavement bridges and traffic services
depreciation cost and interest on investment.
(v) Probable life and salvage value at the end of this period.
The average annual highway cost for a road system may be summed up by
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the formula.
Ca – H + T + M + Cr
where
Ca = average annual cost of ownership and operation
H = average cost for administration and management at head quarters
T = average annual highway operation cost.
M = average annual highway maintenance cost.
Cr = average annual capital cost of depreciation of investment
capital or the capital recovery with return on capital
The annual cost is considered in the economic assessment of highway projects. Instead of
considering the overall cost of a project the annual repayment of a capital loan plus the
interest over a specified period of time of the annual capital cost is considered in the
analysis.
economical proposal among various alternatives, in the analysis for economic
justification of the proposed improvement, it is required to use judgment such as
quantitative selection of the factors in which annual highway cost depends and the
estimation of AADT of each class of vehicle considering the normal increase in traffic
and the generated traffic.
Methods of Analysis
The procedure for the economic evaluation of highway projects consists of
qualification for cost component and the benefits arising out of the project and to
evaluate by one of the methods of analysis.
There are several methods of economic analysis. Some of the common methods
are. Annual-cost Method, Rate-of-Return Method and Benefit-Cost Method.
Annual-Cost Method
The annual cost of each element of capital improvement is found by multiplying
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by the appropriate CRF value calculated for the assume life span. The annual cost Cr
may be found using the relation (Eq. 14.3).
C1 = P. i(1+i)n = P(CRF)
(1+i)n-1
Rate-of-Return Method
There are number of variations for the determination of raw of return of a
highway improvement. In the rate of return method, die interest rate at which two
alternative solutions have equal annual cost is found, If the rate of return of all proposed
projects are known, the priority for the improvement could be established.
Benefit Cost ratio Method
Principle of this method is to assess the merit of a particular scheme by comparing
the annual benefits with the increase in annual cost
Benefit cost ration = Annual benefits from improvement
Annual cost of the improvement
= R–R1
H1-H
Where R = total annual road user cost for axisting highway
R1 = total annual road user cost for proposed highway
improvement
H = total annual cost of existing road
H1 = total annual cost of proposed highway improvement
The benefit-cost ratios are determined between alternate proposals and those
plans dub are not attractive are discarded. Then the benefit cost ratios for various
increments of added investment are computed to arrive at the best proposal. hi order to
justify the proposed improvement, the ratio should be greater than 1.0. However, the
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choice of interest rate would affect the results of the benefit-cost solutions.
Total annual road user cost for proposal B = RB = Rs. 2491,125
Total annual highway cost of proposal C = HC = Rs.3,75,100
Total annual highway cost of proposal C= HC = Rs.2377,245
Benefit – cost ratio,
C = RA-RB = 3081,330 - 2377.245 = 704,085 = 3.546
A HC-HA 375,100 - 176,527 198, 573
Therefore, alternative C is the best one with higher benefit-cost ratio.
HIGHWAY FINANCE
Basic principle in highway financing is that the funds spent on highways
are recovered from the road users. The recovery may be both direct and indirect.
Two general methods of highway financing are:
Pay-as-you-go method
Credit financing method
In pay-as-you-go method, the payment for highway improvements, maintenance
and
operation is made from the central revenue. In credit financing method, the payment
for highway improvement is made from borrowed money and this amount and the
interests are
re-paid from the future income.
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Distribution of highway cost
The question of distributing highway cost among the Government, road-user and
other has been a disputed task in several countries. Many economists are of the view that
the financial responsibility for roads should be assigned only among the beneficiaries on
the basis of the benefit each one receives.
There are several theories suggesting the method of distribution of highway taxes
between passenger cars and other commercial vehicles like the trucks. However in India
the annual revenue from transport has been much higher than the expenditure on road
development and maintenance. Therefore there is no problem of distributing the highway
cost among other agencies. Also the taxation on vehicles is being considered separately
by the states and there seems to be no theory followed for the distribution of taxes
between various classes of vehicles.
Sources of Revenue
The various sources from which funds necessary for highway development
and maintenance may be made available, are listed below:
Taxes on motor fuel and lubricants.
Duties and taxes on new vehicles and spare part including tyres
Vehicles registration tax.
Special taxes on commercial vehicles
Other road user taxes
Property taxes
Toll taxes
Other funds set apart for highways
Highway financing in India
The responsibility of financing different roads lies with the Central Government,
State Governments and local bodies including Corporations, Municipalities, District
Boards and Panchayats.
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Taxes levied by Central Government for highway financing are:
Duties arid taxes on motor fuel
.Excise duty on vehicles and spare parts, tyre etc.
Excise duty on oils, grease, etc
Taxes levied by the State Governments include:
Registration fees for vehicles and road tax
Permits for transport vehicles
Passenger tax on buses
Sales tax on vehicle parts tyre etc.
Fees on driving licenses
Taxes levied by local bodies are mainly the toll tax.
Ever since the introduction of Central Road Fund (CRF) in the year 1929 by taxing motor
fuel, this has been the main source of finance for the State Government to meet the road
development needs, without having to go through the time consuming process of special
sanctions each time. However of late the CRF is also being merged with the general
revenue, in March 1976 the Lok Sabha has passed the resolution Of the Ministry of
Transport ensuring