Guidelines - IMESA - Low Cost Road 09Jun2005rev

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SECONDEdition MG 1GUIDELINES

FOR DESIGN, CONSTRUCTION ANDMAINTENANCE OF LOW COST ROADS

AND ASSOCIATED DRAINAGE

I.M.E.S.A. Municipal Guidelines

FOR FURTHER INFORMATION PLEASE CONTACT

THEKWINI MUNICIPALITY

P O Box 244

Pinetown 3600

APRIL 2006

Edition MG 1. pp 1 18, Durban, South Africa, 2006

J PIETERSEN TEL. (031) 7182404


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GUIDELINES FOR DESIGN, CONSTRUCTION ANDMAINTENANCE OF LOW COST ROADS AND

ASSOCIATED DRAINAGE

CONTENTS

Chapter DescriptionPage

1. INTRODUCTION ...................................................................... 1

2. SOCIO-ECONOMIC CONDITIONS.............................................. 2

3. ROAD CATEGORIES................................................................ 23.1 Minor arterials ...............................................................................33.2 Residential Access Roads ............................................................3

4. SUBGRADE CONDITIONS ........................................................ 44.1 Geotechnical Investigation............................................................44.2 Material Depth ..............................................................................5

4.2.1 Minor Arterials.......................................................................54.2.2 Residential Access Roads ....................................................5

5. GEOMETRIC ROAD DESIGN..................................................... 5

5.1 Road Cross Section......................................................................7

6. PAVEMENT DESIGN ................................................................ 96.1 Minor Arterials...............................................................................96.2 Residential Access Roads ..........................................................10

7. STORMWATER DRAINAGE DESIGN ........................................ 107.1 Stormwater Drainage Design......................................................107.2 Return Period..............................................................................14

8. QUALITY CONTROL............................................................... 14

9. SAFETY................................................................................ 15

10. ENVIRONMENTAL ................................................................. 15

11. ROAD AND STORMWATER ASSET MAINTENANCE .................. 15

12. REFERENCES....................................................................... 17

13. ACKNOWLEDGEMENTS......................................................... 18


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1. INTRODUCTION

The purpose of this document is to provide municipalities with guidelines fordesign, construction and maintenance of low cost/volume roads andassociated drainage.

Low volume roads are defined as minor arterial or residential access roadswhich carry less than 500 vehicles per day, including up to 20 % commercialvehicles and non-motorized traffic.

This document is not intended as a design manual, rather it seeks to collateavailable design guidelines with experience gained over years into a set of

guidelines which are appropriate for given circumstances taking cognizanceof geographical, geotechnical or socio-economic factors.

The emphasis is on the improving of existing conditions in informalsettlements or townships, thereby improving quality of life, in a most cost-effective manner.

It is also important to ensure that projects are implemented as part of aphased development; i.e. very basic improvements can be implemented first,with further enhancements added as the desired level of service increaseswhen more funds become available.

Low cost roads should be constructed to levels where they can effectively beupgraded. The emphasis of the Municipality should be to optimize theirexpenditure on roads, drainage and maintenance over a number of years, inaccordance with a strategic road infrastructure maintenance managementsystem or plan. (An example of such a plan, referred to as RIMMS, isavailable from the eThekwini Municipality on request from the MaintenanceManagement). ( 1 )

Such a plan should also include planned improvements to the road drainageas to reduce risk of flooding of properties which could result in damage to

property and loss of life.

The provision of services to underprivileged communities is a rewarding task,but must be coupled with a vision of how the improved standard of life canbe maintained.

It is therefore imperative to have a strategic road infrastructure maintenancemanagement system or plan, which will protect the investment as well asprovide local employment and a sense of ownership to the community.


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2. SOCIO-ECONOMIC CONDITIONS

These guidelines are supportive of sustainable poverty alleviationprogrammes for example the Expanded Public Works Programme(EPWP), structured in the interests of the poor.

A substantial amount of the overall annual budget allocation must bechanneled towards the implementation of the EPWP to:

Create employment opportunities for the unemployed

Develop skills within communities through EPWP on-the-job skills

programmes

Capacitate Small Medium Macro Enterprises (SMMEs) to executeEPWP work within communities by facilitating the transfer ofsustainable technical, managerial and financial skills.

The use of Labour Intensive methodology in construction andmaintenance will significantly reduce poverty within a City or Town andgive access to Government Grant Funding.

Since not all projects are 100% conducive to labour intensive construction

methods, each should be assessed on its merits and justification providedif it is considered that labour intensive construction methods cannot beimplemented on a particular project.

3. ROAD CATEGORIES

For the purpose of this document, two street categories are considered asbasic access streets:

Minor arterials (Bus routes)

and

Residential Access roads


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The following table serves as a guide to the road design:

TYPICAL ROAD CHARACTERISTICS (

2

)Minor Arterials Residential Access Roads

Description andFunction

Low Order MixedPedestrian andVehicle Route

Pedestrian and vehicle access route

Level of service(LOS)

Moderate to Low Low

Traffic (vehiclesper day)

>75 < 500


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The width of the access roads can be reduced to 3m. Should the road lengthexceed 80 m, passing bays should be added to the road width at 50 mspacing.The roads are normally built to gravel standard, as surfacing cannot be

justified. However should the road be used as drainage medium, effective useof rollcrete can be made (see Section 5).

There is an option to do nothing during the first phase of a townshipdevelopment. In this case it will be better to leave the insitu vegetation inplace in order to prevent erosion. No form of stormwater control should beimplemented.At this stage it is better to retain a sheetflow scenario rather than toconcentrate flows of stormwater which can result in damage to property.

Gravel of roads and the creation of a stormwater control system can beundertaken in subsequent years when funding is available.

4. SUBGRADE CONDITIONS

4.1 Geotechnical Investigation

Despite budget constraints, it is very important to undertake geotechnicalinvestigations in order to accurately determine subgrade conditions.

The lower or more variable the quality of the insitu subgrade materials, themore important it is to ensure that the designer is fully aware of theconditions. A high water table combined with very plastic material can resultin very expensive subgrade costs as additional layers will be required.

Despite the fact that the geotechnical conditions are known at the designstage, there is still a high risk of new low cost road failing. Since these roadshave relaxed layerwork material requirements, it is implied that the

percentage of the roadworks can be expected to have problems and provisionneeds to be made for this in the strategic road infrastructure maintenancemanagement plan.

It is thus imperative that a thorough understanding of the geotechnicalconditions fully addresses current and future costs and the likely maintenancerequirements.


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4.2 Material Depth

The term material depth is used to denote the depth below the finished roadlevel to which the soil characteristics have a significant effect on thepavement behaviour.Below this depth it is assumed that the strength and density of the soils arenot significantly affected by the applied loads.

It is important to note that if the road is built in stages, the material depth mustbe achieved by the time the road is surfaced.

4.2.1 Minor Arterials

The material depth accepted for Minor Arterials is 600 mm, which refers to thethickness of the layers which are constructed of material which is better thanG10 quality. ( 3 )

4.2.2 Residential Access Roads

The material depth accepted for Residential Access Roads is 300 mm, whichrefers to the thickness of the layers which are constructed of material which is

better than G10 (3

) quality.This is achieved by scarifying and re-compacting the insitu material if thematerial is of G 9 ( 3 ) quality or better. If the insitu material do not make thespecification of a G9, an additional layer will be required as a selectedsubgrade layer.

5. GEOMETRIC ROAD DESIGN

The functional classification of basic access streets indicates that trafficvolumes are so low that the traditional design guidelines are not applicable in

most cases.

Non-traffic related factors such as layout planning, stormwater managementand drainage, climate, environment, topography and in-situ materials have amajor influence on the design of basic access streets.

Figures 5.1 ( 2 ) below illustrate the decision process for the design of basicaccess streets. If the decision is taken not to pave a basic access street,attention should be paid to erosion protection, the quality of the insitu materialand the quality of the wearing course (if required).


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Fig 5.1 Flow diagramme for decision process

Drainage andlayout planning

Design of basicaccess streets

Erosion problems

Need erosionprotection

Is in-situ materialacceptable?

Is dust palliativeon gravel

adequate?

Select surfacingtype

Use dust palliative

Design gravelthickness

Insitu base acts aswearing course

No

NoYes

Yes

Base, subbase and subgrade meet material specifications

No Yes


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Erosion-prone in-situ materials should be identified.

The length of erosion- free in-situ material can be determined if the gradientand basic material information is available. If erosion problems are identified,erosion protection must be provided. Surface stabilizers may be considered inthis regard.As shown in table 7.1, in-situ material can be used without a surfacing if itmeets the appropriate material standards for basic access streets. The gravelused should comply with that as specified in TRH20 ( 5 ).

A gravel road may be regarded as a long-term facility or as an interim steptowards a paved street. This will influence the level of service with regard tostormwater facilities and geometric considerations.

5.1 Road Cross Section

Typical cross sections of the road profiles for the two road categories of roadare shown in the figures below.

Minor arterials


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Residential Access Roads


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6. PAVEMENT DESIGN

The traffic volume and loading will determine the pavement design. Use aPavement Design Engineer if in doubt.

6.1 Minor Arterials

These roads can be constructed in two stages as funds become available.

Dry / Moderate climate Wet climate

150 mm

On

G 7 compacted to95 % ModAASHTO density

150 mm G 6 compacted to95 % ModAASHTO density

150 mm

On

G 9 compacted to93 % ModAASHTO density


Stage 1

150 mm G 10 insitucompacted to 93 %Mod AASHTOdensity

150 mm G 10 insitucompacted to 93 %Mod AASHTOdensity

Stage 2 SealOn

Sealon



Table 6.1 Typical Pavement design for Minor Arterials

The availability of the different quality materials will determine the final pavementdesign


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6.2 Residential Access Roads

Likewise these roads can be constructed in two stages as funds becomeavailable.

Stage 1 Do nothing, do not strip vegetation or create earthdrains

125 mm

OrRollcrete if road to be used as drainage channel

150 mm

On

G 7 compacted to 93 % Mod AASHTO density

Stage 2

150 mm G 10 insitu compacted to 93 % Mod AASHTOdensity

Table 6.2 Typical Pavement design for Residential access roads

7. STORMWATER DRAINAGE DESIGN

7.1 Stormwater Drainage DesignThe prime function of an urban stormwater drainage system is to collect therunoff from the roads and properties and to convey this flow back to thenatural drainage system.

New townships must be designed by the Town Planner and the Engineer foreffective low cost servicing which suits the natural topography. Townshiplayouts must not include residential or business sites which are situated onthe low side of watercourses or within the flood plains but rather convert theseareas as Public Open Spaces.

Structural measures include the installation of concrete channels, stonepitched channels, rectangular channels, pipe culverts, dished concrete roadcrossings, including road surfaces as a drainage channel. The most cost-effective system is in the latter case, by retaining the stormwater as roadsurface flow until it can be returned to the natural water course.

Type of low volume traffic roads for consideration of road surface flow, are:

- Gently sloping contour road which control slow flowing stormwater withoutthe need for special protection;


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- Steep roads down the contour, designed in rollcrete which can handle theflow within the surfaced roadway without the damage of scour or erosion.

The most effective control of the flow is gained by ensuring that the crossfallof the road runs counter to the slope of the natural ground.

Once the capacity of the surfaced road has been exceeded, it becomesnecessary to divert the flow into a formal piped or surface drainage system.

With cost constraints, surface drains such as stone pitched or concretetrapezoidal drains present a practical alternative to subsurface piped drains.

Rectangular channels can be cost-effective, utilize minimal space in the roadreserve and allow unhindered access to properties when properly designed.


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A suggested guideline range of road gradients is given below.

ROAD SURFACING GRADIENTS

GRAVEL 0 3%

SURFACE TREATMENT 3 5%

PREMIX (25 mm) 3 10%

PREMIX (40 mm) 5 12%

CONCRETE NO LIMIT

Table 7.1: Suggested road surfacing on various grades

For unpaved roads, side drains are typically used with concrete dishes atintersections to convey water across the road.

Where steep longitudinal gradient of a side drain occur and the nature of theinsitu material needs to be carefully analyzed to determine the nature of scourprotection that is required.


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The table below provides the scour velocities for various materials andguidelines on the necessity to line or pave channels.

Material AllowableVelocityWithoutScouring

Max GradientFor UnlinedEarth SideDrains (%)

Gradient AtWhich CheckDrains Can

Be Used (%)

Gradient WhereLined ChannelRequired (%)

Fine Sand 0,6m/s 2% 2 10 10

Loam 0,9 2% 2 10 10

Clay 1,2 5 5 - 10 10

Gravel 1,5 5 5 10 10

Soft Shale 1,8 7 7 10 10

Hard Shale 2,4 N/A N/A 10Hard Rock 4,5 N/A N/A 10

Table 7.2: Scour Velocities for Various Materials and Guidelines for useof Scour Protection.

7.2 Return Period

The criteria for the design of stormwater drainage systems of Minor Arterialsand Residential Access Roads should use the recommended return periodsfor drainage design as follows:

RAINFALL DATA FOR RETURN PERIODS

Normal design of system/side drains

Design of critical elements/pipes at low points

Prevention of catastrophic damage

1 : 3 year

1 : 10 year

1 : 50 year

Table 7.3 Design return periods

8. QUALITY CONTROL

The normal quality control systems as specified in SABS 1200 should applyfor the construction of low volume traffic roads.For roads with a gravel wearing course, TRH 20 Guidelines for the structuraldesign, Construction and Maintenance of Unpaved roads ( 5 ), shall apply.


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9. SAFETY

The Municipality must comply at all stages with the Occupational Health andSafety Act 85 of 1993 as amended and Regulations. ( 4 )

A copy of this document must be available at all times.

10. ENVIRONMENTAL

The Municipality must comply with the latest act for Environmental andConservation being Act 73 of 89 as amended.

11. ROAD AND STORMWATER ASSET MAINTENANCE

Section 63 of the Municipal Finance Management Act (MFMA) pertainingto Asset and liability management states that:

1) The accounting officer of a municipality is responsible for themanagement of:

a) the assets of the municipality, including the safeguarding andmaintenance of those assets; andb) the liabilities of the municipality.

2) the accounting officer must for the purposes of subsection (1)take all reasonable steps to ensure:

a) that the municipality has and maintains a management,accounting and information system that accounts for theassets and liabilities of the municipality;

b) that the municipalitys assets and liabilities are valued in

accordance with standards and General Acceptable MunicipalAccounting Practice (GAMAP); andc) that the municipality has and maintains a system of internal

control of assets and liabilities, including an asset andliabilities register, as may be prescribed.


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All the assets must be listed in an Asset Register and the MaintenanceManagement Plan must include:

Risk assessment

Use and condition of Asset

Value assessment and depreciation.

A typical flow diagram of a plan is shown in Figure 11.1 below

ASSET MANAGEMENT CYCLE

Table 11.1: Asset Management Cycle

Acquire

Dispose Maintain

Service Delivery

Financial Aspects

Asset Purchase

Asset

Maintenance

Plan

Assess use and

condition

Record Asset in

a Register

Assess Asset

Value

Budget for each

asset

Asset Renewal /

Replacement /

Disposal

Risk

AssessmentAsset

Management


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12. REFERENCES

1. Road Infrastructure Maintenance Management System (RIMMS) availablefrom the Deputy Head, Roads Provision Ethekwini Municipality031-300 2911

2. Guidelines for Human Settlement Planning and Design, CSIR Buildingand Construction (Red book)

3. National Institute for Transport and Road Research(1987): Guidelines forroad construction materials, TRH 14, CSIR Pretoria

4. Occupational Health and Safety act 85 of 1993 and Regulations, ThirdEdition, LexisNexis Butterworths

5. CSRA (1990) The structural design, Construction and maintenance ofUnpaved roads Draft TRH 20, CSRA


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13. ACKNOWLEDGEMENTS

The document was compiled by the KZN Roads, Stormwater & Transportationworking group.

J Pietersen eThekwini Municipality ChairmanZ Mller eThekwini MunicipalityB Govender eThekwini MunicipalityL Cloete MCJ Engineers Consultant

Draft documentation Argus Gibb

Documents

Guidelines - IMESA - Low Cost Road 09Jun2005rev