Upload
clifford-njah
View
226
Download
6
Embed Size (px)
Citation preview
7/31/2019 Coren Report 3
1/32
INTRODUCTION
Generally, speaking the engineering profession is one which experience is found to
be a priceless asset. Not much difference exits between a Lay man and an
inexperience engineer.
This report is aimed at attempting to present a very brief but concise and practical
record of some engineering activities I undertook since after my graduation as a
Civil Engineer from the University of Port Harcourt in 1988 to date.
It must be stressed here that for reasons of time and space constraints, this report is
made as vivid as possible such that some engineering details are ignored. I wish to
stress further that this document is not a chronicle of all the engineering activities I
encountered, but a part of a whole, specifically presented for the purpose of
meeting up with the requirements for registration as a member of the Council for
the Regulation of Engineering in Nigeria (COREN).
For purpose of simplicity, this report is divided into three (4) chapters. Each of
these chapters presents the experience gained in the various fields of Civil
Engineering.
Chapter one discusses my experience in the field of Highway Engineering. Chapter
two discusses on Foundation / Geotechnical Engineering, chapter three deals withn
Structural Engineering, while Chapter four discusses on hydraulics Engineering.
My experience, as presented in the various chapters, is drawn from my ten-year
service with Risonpalm Limited and my present employer Nigeria Agip Oil
Company Limited.
At Risonpalm Limited (1991-2000), I rose from the position of Civil Engineer to
Head of Engineering services department. My responsibilities included design,
supervision and construction of various civil engineering structures / facilities and
maintenance of buildings and roads. It was also my responsibility to supervise
Community development projects in the Land owning Communities.
From the year 2000 till date, I have been working as a Community projectEngineer for Nigeria Agip Oil Company (NAOC) Limited. In this capacity, I
design, estimate and oversee the construction of roads drainages, various buildings,
water schemes and other civil engineering facilities in NAOCS land owning
communities (Swamp and Land areas).
Extracts of these experiences are put together in this document to represent a small
portion of my 15 years practice as a Civil Engineer.
1
7/31/2019 Coren Report 3
2/32
CHAPTER 1
HIGHWAY ENGINEERING
One of the most frequently demanded facilities by communities where Nigeria
Agip Oil Company (NAOC) Ltd operates is road.
As a community project Engineer, it is my responsibility to carryout detailed
engineering of the roads and present cost estimates.
Depending on the terrain, different types of roads are considered. For the dry land
areas, flexible pavements were mostly adopted while for the swampy areas, either
rigid pavements or stabilized flexible pavements were considered. Basically, for
whatever type of pavement construction under consideration, an appropriate road
profile design is carried. During this design, some guiding principles are foundinevitable. These are outline in section 1.1.1.
1.1.1 ROAD PROFILE DESIGN
Route surveying is carried out to be able to select the most suitable location for the
roads. In carryout this task, I keep certain guiding principles in mind. However, the
actual route selected in each situation is the one that represents the best
compromise solution. The primary guiding principle adopt during route surveying
includes the following:
(a) The road should be located where it can best meet the major traffic desire
lines and be as directed as possible.
(b) Grades and curvatures are kept to the minimum necessary to satisfy the
service requirements of the highway.
(c) Avoiding sudden changes in site distances, especially near junctions.
(d) Avoiding having a sharp horizontal curve on or adjacent to a pronounced
vertical curve.
(e) Sitting roads through undeveloped areas along the edges of large park lands
and away from highly developed, expensive land areas.
(f) Locating (as much as possible) a new road on existing ones, so as to
minimize the use of farm lands and reduce the total initial and maintenance
cost.
2
7/31/2019 Coren Report 3
3/32
(g) Never having two roads intersecting near a bend or at the top or bottom of a
hill.
(h) For river crossings, roads are kept at right angles to the stream center line.
(I) Bridges are not to be located on or adjacent a highway curve.
(j) Care is taken to avoid possible landslides in hilly terrain.
(k) To minimize drainage problems, routes are located on high ground in place
of the one a valley.
(l) As much as possible, marshes and other low lying lands subject to flooding
are avoided.
(m) Roads are located on soil which will require the least pavement thickness
above it. That is, the soil with high valve of CBR.
(n) Where possible, cuts and fills volumes are balanced to minimize total cost of
earth works.
1.1.2. LOCATION SURVEY IN RURAL AREAS
In establishing the route of a proposed road in the rural communities, the first step
I take requires fixing the two points that the road intends to join, in the area of
interest, which will include all conceivably feasible routes between the points. This
area is then searched and a number of broad zones are selected within which it is
decided to concentrate further searches and selections. This process is continueduntil a particular zone is narrowed down to a route location. The process involves
continuous searching and selection with such factors as: Topography,
soil/geological details, land use, population distribution, political, social and
environmental costs influencing the selection process at each decision making
stage.
Good reconnaissance can be the greatest single money saving phase in the
construction of a new road. Hence I always recommend for ample provision of
logistic support by the company while I put in a lot of time for this stage of
location investigation.
During sites visits to the areas in question, I make enquires and obtain information
from the chiefs and elders regarding the hills, water ways and land use. Some of
the information like the site reports on existing routes, building foundations and
pipelines (water and/or oil) were obtained from the engineers of these existing civil
engineering projects in the area.
3
7/31/2019 Coren Report 3
4/32
1.1.2 PRELIMINARY SURVEY
The next step I take after location survey is to carryout a preliminary survey of the
area. This is made for the purpose of collection all the physical information which
may affect the location of the road. These information include, the shape of the
ground, right of way of limits, positions and invert levels of streams and ditches,
the positions of trees, banks, ledges, bridges, culverts, existing roads, power andpipelines, houses and monuments.
The next activity I carryout is to translate all the features mentioned above into
profiles, cross-sections and sometimes into maps, which assists me to determine
preliminary grades and alignments and prepare cost estimates.
1.1.4 PAVEMENTS DESIGNED AND CONSTRUCTED
I have carried out a lot of pavement designs and construction as a community
project engineer for Nigeria Agip Oil Company (NAOC) Ltd and as an EstateEngineer for Risonpalm Ltd.
(A) FLEXIBLE PAVEMENT DESIGN & CONSTRUCTION
Below are some of the flexible pavements I designed, cost and supervised their
construction
4
7/31/2019 Coren Report 3
5/32
S/N PROJECT TITTLE LENGTH
OF ROAD
PROJECT
COST (N)
5
7/31/2019 Coren Report 3
6/32
1 Construction of Aakor street, Omoku 900m 13,500,000
2 Construction of Iyasara street, Omoku 1.10Km 16,500,000
3 Construction of police/Eze Ohali street,
Omoku
600m 9,000,000
4 Construction of Cemetry road, Omoku 850m 12,750,000
5 Construction of Court road, Omoku 2.10Km 31,500,000
6 Construction of Erema street Omoku 1.10Km 16,500,000
7 Construction of Oba/Tand road, Omoku 2.85Km 42,750,000
8 Construction of Egbema street, Omoku 650m 9,750,000
9 Construction of Abua street, Omoku 400m 6,000,000
10 Construction of Umuohali street, Omoku 1.05Km 15,750,000
11 Construction of Umuchikere street, Omoku 810m 12,150,000
12 Construction of Palace road Omoku 1.10Km 16,500,000
13 Construction of Various 10 road, Obrikon 8.21Km 123,150,000
14 Construction of 6 internal roads, Aggah 5.66Km 84,900,000
15 Construction of Ngbede Aggah roads 4km 60,000,000
16 Construction of Mgbede internal roads 4.5km 67,500,000
17 Construction of Elekwuru roads 5.5km 82,500,000
18 Construction of Ameshi road, Oguta-Imo state 2.71Km 40,650,000
19 Construction of Akaraolu intend roads 3.41Km 51,150,000
20 Construction of Oburunwahor street Omoku 1.00Km 15,000,000
21 Construction of Market road, Omoku 300m 4,500,000
22 Construction of S.O. Masu road, Omoku 450m 6,750,000
23 Construction of Umunkaru street, Omoku 1.17Km 17,550,000
6
7/31/2019 Coren Report 3
7/32
24 Construction of Okwuzi road 4km 60,000,000
25 Construction of Aggah road 4km 60,000,000
DESIGN PHILOSOPHY AND METHOD
The design of a flexible pavement is aimed at ensuring that the stresses transmitted
on the road surface are sufficiently reduced in order not to exceed the supporting
capacity of the subgrade.
In the design of this type of pavement, thorough examination is given to the
elements that constitute it. These are surface course, Road base and sub-base.
The design method I used is the California Bearing Ratio (C.B.R). With this
method, attempts are made to evaluate the stability of the subgrade, so that the
thickness of the overlying material needed to safely distribute the applied wheel
load to it can be estimated. Design curves relating pavement thickness with C.B.R
of the underlying materials were used to determine the thicknesses of the various
components of flexible pavement. From the results of designs on various roads
above, the following asphalt pavement thickness appear appropriate
Light Traffic : 50mm
Medium Traffic : 75mm
Heavy Traffic : 100mm
Some roads whose sub-bases are of very weak soil required crush-stone bases or
soil-cement stabilization. The thicknesses of these bases are obtained from
calculations.
As an example one of the roads I designed and constructed Okwuzi 4km road is
found on a subgrade having CBR of 4%.
It was anticipated that 300 vehicles exceeding 30kN was going to use this road.
The road is to be of 2 lanes in each direction.
Using table 1: Lane Distribution Factors on multilane roads; it is seen that
100% of 30kN vehicle are used for 2 lane roadway.
Using Fig. 1: Flexible pavement design curve; the appropriate curve for this
design is that of D7
7/31/2019 Coren Report 3
8/32
The required thickness of pavement for a subgrade of CBR = 4% is about 17
inches (425mm). However, the total pavement thickness is to be made up of
Portland cement stabilization, crushed stone and asphalt concrete pavement.
Generally, cement stabilization is known to produce a minimum C.B.R of 9%which will give (from flexible pavement design curves) a total pavement thickness
of about 11 inches (275 mm). Hence total thickness of cement stabilized sub-base
is 425mm-275mm=150mm (6 inches). For crushed stone base, a C.B.R of 75% is
assumed. With this C.B.R value the curve shows that a pavement depth of 3 inches
(75mm) is remaining. Thus the total depth of the crushed stone base in 11 inches-3
inches:(275mm-75mm) = 8inches (200mm)
Therefore, thickness of asphalt concrete required to complete the pavement section
= 275mm - 200mm =75mm (3 inches)
This is a typical design for the roads listed in section 1.1.4.
For roads with considerably higher values of C.B.R, the cement stabilization and
stone base application are not necessary.
PHOTOGRAPHS OF VARIOUS STAGES OF FLEXIBLE PAVEMENT
CONSTRUCTION
1a Site Clearing/Stripping
1b Grading of road
1c Filling with Laterite
1d compacted angcambered road segment
1e MC 1 priming
1f Asphalt paving
1g Rolling of hot Asphalt
8
7/31/2019 Coren Report 3
9/32
(B) RIGID PAVEMENT CONSTUCTION
Below are some areas where I constructed rigid pavements:
1. Mill (factory) floor Risonpalm Limited, Ubima Estate, Rivers State (figures
2a 2h).
2. Kemmer town toad, Twon Brass (Bayelsa State) (Fig. 3)
3. Secondary school road, Twon Brass (Bayelsa State) (Fig. 4.)
4. Concrete Road, Akakumama-Okoroma/Tereke L.G.A Bayelsa State (Fig. 5.)
5. Egbebiri concrete road and drains (fig 6a- 6d)
FACTORS CONSIDERED DURING DESIGN AND CONSTRUCTION OF
RIGID PAVEMENTS.
Rigid pavements are more suitable and more economical at areas where the C.B.R
is extremely low and the construction of asphalt pavement may fail almost
immediately after construction.
In the design of rigid pavements, I consider four basic factors. These are:
1. Amount, type and weight of present and anticipated traffic which is similar
to that required for flexible pavement.
2. Supporting power and character of the subgrade.
3. Climatic region in which pavement is to be constructed.
4. Strength and quality of the concrete to be used.
These factors determine the quality and thickness of concrete required for the
pavement. As a result of the expansion and contraction of concrete, I construct
concrete pavements in segments, allowing for gaps between them. These openings
serve as expansion joints. During construction of the slabs, allowance is made for
at least 20% of loads to be transferred across the openings at corners formed by the
intersection of transverse cracks or joints with the free edge of a pavement withthis provision, the corners of the slabs are said to be protected.
I adopt three (2) methods of transferring loads from one slab to the other. These
methods are:
1. Slip Dowels: These are usually smooth round bars 20mm to 25mm
diameters, 325mm to 500mm long and spaced 200mm to 450mm apart.
9
7/31/2019 Coren Report 3
10/32
Square bars, steel pipes and small channels are sometimes used. (See figure
2c)
2. Sills: A mental support, embedded in one slab end extending under the
bottom edge of the adjacent slab, is sometimes used.
. REINFORCEMENT OF RIGID PAVEMENT
Reinforcement steels of prefabricated sheets are the ones I used frequently. During
usage, I ensured that the reinforcement was free from oil, dirt, loose rust and scale.
The prefab sheets overlay by more than one complete mesh.
SURFACE FINISH
The surface of the slabs, after final regulation, is usually brush-textured in a
direction at right angles to the longitudinal axis of the carriage way.
CURING
After casting of concrete slabs, curing is essential to provide adequate protection
from evaporation and against heat loss or gain by radiation, and thereby allow the
concrete to attain its designed strength. (See figure 6).
JOINTS IN PAVEMENT SLABS
All pavements I constructed are divided into individual panels by joints in both the
longitudinal and traverse directions.
In attempt to prevent differential vertical movement between adjacent slabs, dowel
bars are provided, set at the mid-depth of the slab and parallel to the longitudinal
axis if the road. One end of the dowel bar is de-bonded, so that it does not stick to
the concrete of one slab; the other end is cast into the concrete of the adjacent slab.
(See figure 7)
10
7/31/2019 Coren Report 3
11/32
CHAPTER 2
2.0 FOUNDATION / GEOTECHNICAL ENGINEERING
A building is generally divided into two parts. The superstructure is the sectionabove the ground level while the substructure is below the ground is known as
foundation. It is therefore obvious that almost all civil engineering facilities are
supported by foundation and hence foundation engineering plays significant roles
in engineering projects.
MY EXPERIENCE IN FOUNDATION/ GEOTECHNICAL ENGINEERING
Since almost every engineering structure rests on foundation, every practicing
engineer will regularly be in contact with the challenges of
foundation/geotechnical engineering.
In my practice, I have designed several types of foundation which can broadly be
classified as either shallow or deep. However, which ever foundation is in
question; I consistently look out for having substructures resting on stable soils
with tolerable deformations. In course of my practice, it became clear that the earth
under the foundations is the most variable of all the materials that are considered in
the design and construction of an engineering structure. Within a small region, the
soil may vary from very soft clay to a hard rock. Hence in major projects (those
that exert great loads on the soils) I always consider detailed soil survey to
determine their engineering properties.
The survey may include sinking of drill holes or trial pits to obtain in-situ test
results. In other cases soil samples are collected and sent for laboratory analysis.
Results obtained helps in the determination of safe earth bearing pressures and the
calculation of possible settlements of the structure, if required.
For minor structure, there are basic standards adopted for the safe bearing
pressures for the various soil types.
I had designed the five different types of shallow foundations known, namely;
isolated footings, continuous footings, combined footings, mats or raft and floating
mats. These were found while designing and constructing various buildings,
retaining walls and tank foundations.
11
7/31/2019 Coren Report 3
12/32
Actually, my choice of foundation type depended on such factors as soil bearing
capacity, types of columns loadings, distances between adjacent columns,
closeness of columns to property line etc.
In the design of foundations the serviceability limit states are adopted since
settlement takes place during the working life of the structure.
Values of safety factors used are:
1. Dead plus imposed load = 1.0G + 1.0Qk
2. Dead plus wind load = 1.0Gk +1.0Wk
3. Dead plus imposed plus wind load = 1.0Gk +0.8Qk +0.8Wk
With these partial factors, it is very unlikely that the maximum imposed loads and
worst wind load will occur at the same time.
In all my calculations, I make sure that:
1. The foundation must be properly located considering any future influence
performance, particularly for footing and mats.
2. The soil supporting the foundation must be safe against shear fail.
3. The foundation must not settle or deflect to a degree that can result in a
damage to the structure or impair its functioning.
4. The foundation should be safe against sliding and overturning.
These requirements ordinarily should be considered in the above order.
The first one involves many different factors, most of which cannot be evaluated
analytically and have to be answered by engineering judgment.
The second is specific. It is analogous to the requirement that a beam in the
superstructure must be safe against breaking under its working load. An answer to
this requirement can be obtained analytically.
Answer to the third requirement can be obtained only partly. Settlement of a
structure under the working loads depend basically on the type of foundation and
soil, and the same can be estimated analytically. However, exact evaluation of the
tolerances of different structures with respect to different structures with respect to
different soils is difficult to estimate and hence one has to depend for this on the
engineering judgment keeping in view the functioning of the structure.
12
7/31/2019 Coren Report 3
13/32
The fourth requirement is specific and evaluated after obtaining relevant earth
pressure against foundation.
2.1 REINFORCED EARTH STRUCTURES
Reinforce earth is a construction material comprising soil that has been
strengthened by tensile elements such as metal rods and/or strips nonbiodegradable fabrics (geotextiles), geogrids, and the like.
One of Nigeria Agip Oil Companys flow station (Obama in Bayelsa) was
threatened by severe erosion at the water front. The need to check this hazard
arose.
As a project engineer covering this area of operation, I thought of means of
protecting the eroding shore.
A system that quickly came to mind was the use of non biodegradable fabrics
made from petroleum polyester, polyethylene, and polypropylene.
The form of geotextile used was the knitted type which is formed by the
interlocking of a series of loops of one or more filaments or strands of yarn to form
a planar structure.
Figures 8a 8c show the various interlocking materials that were knitted to form
the planar structure shown in figures 8d - 8f.
Figure 8g shows the non biodegradable fabric used in the system.
Basically, geotexiles serve as filters and reinforcements.
GEOTEXTILES AS A FILTER
When placed between two soil layers, one coarse grained and the other fine
grained, the fabric allows free seepage of water from one layer to the other.
However, it protects the fine-grained soil from being washed into the - grained
soil.
13
7/31/2019 Coren Report 3
14/32
GEOTEXTILES AS REINFORCEMENT
The tensile strength of geofabrics increases the load bearing capacity of the soil.
This increase in bearing capacity interprets to mean reinforcing the soil.
Exploiting these two all- important properties, geotextiles served as a very
dependable system used to the check the erosion at the water front of the flowstation.
14
7/31/2019 Coren Report 3
15/32
CHAPTER 3
3.0 STRUCTURAL ENGINEERING
Civil engineering structures are numerous. Below are some structures I have
designed and constructed as practicing engineer:
Buildings (Low and high rising).
Retaining walls/water retaining structures.
Concrete jetties.
Concrete culverts.
STRUCTURAL DESIGNS
For the purpose of this work, time and space may not permit the presentation of
information and details relating to most of the designs I carried out in area
mentioned in section 2.2. Hence, I shall only give high lights on where thestructures are located, design procedure & photographs.
Of these structures, the retaining wall has been chosen as design project for this
report.
BUILDINGS
I have carried out quite a lot of building designs and construction in the Port
Harcourt areas and its environs. The buildings range from bungalow to three (3)
story buildings. In all designs, I undertook, & employed the philosophy of limit
states design, the purpose of which was to achieve acceptable probabilities that a
structure will not become unfit for its intended use. The two principal types of the
limit states are those of ultimate and serviceability.
Generally, the relative importance of each limit state varies according to the nature
of the structure. For instance in buildings & designed, the ultimate limit state was
taken as the crucial one on which the designs were based even though durability
and fire resistances (serviceability limit states) influenced initial member sizing
15
7/31/2019 Coren Report 3
16/32
and concrete grade selection. Checks are also made to ensure that serviceability
limit states like: Deflection and cracking were not exceeded.
During analysis and designs of a structure for a particular limit state, all possible
variable parameters such as constructional tolerances, loads and material strengths
were considered. The design code use was BS8110.
CONCRETE MIX DESIGN
The objectives of concrete mix design are:
i. To obtain a workable fresh concrete.
ii. Attain a characteristic compressing strength at 28 days.
iii. Assure durability of the concrete.
The chosen mix ratio for the design is 1:2:4 (being proportion of cement to fineaggregate to coarse aggregate either by weight or by volume).
A specified characteristic strength of 20 N/mm2 is here adopted for design this to
corresponds to U300c in the imperial system.
MARGIN FOR DESIGN MIX
It is usually necessary to design the mix to have strength greater than the specified
characteristic strength by an amount called the margin. Thus:
Fm = Fc + Ks
Where Fm =Target means strength
Fc = specified characteristic strength
Ks = the margin
For a 5% defective level, K is taken as 1.64.
Hence Fm = Fc + 1.64S.The standard deviation used in calculating the margin is based on results obtained
using the same plant, material and supervision. However in the absence of relevant
information, I used values extracted from line A, of figure 2.
From figure 2, we have S = 8.0 N/mm2 for Fc = 20 N/mm2
Hence the target strength is computed as follows:
16
7/31/2019 Coren Report 3
17/32
Fc =20 + 1.64 X 8 = 33.12 N/mm2 .
MIX DESIGN PROCESS FOR GRADE 20 CONCRETE (Fcu=20 N/mm2 )
1. Target strength =33.12 N/mm2.
2. From table 2, for ordinary port land cement, crushed, the compressive strength
at 28 day in 47N/mm2, for a free water cement ratio of 0.5.
3. From figure 3, using the compressive strength of 47N/mm2 and the target of
33.12N/mm2, the free water cement ratio is 0.55.
4. Determination of free water content depending upon type and maximum size of
aggregate to give a concrete of the specified slump of 10mm-30.
Hence from table 2 aggregate size of 20mm, crushed and a slump of 10mm
30mm, free water content is 190 Kg/m3
5. Cement content = free - water content
free water/cement ratio
= 190/0.55 Kg/m3
= 346 Kg/m3
6Total aggregate content = D Wc Wfw
Where D = Wet density of concrete (Kg/m3)
= 2400kg/m3
Wc = The cement contents (Kg/m3)
Wfw = The free- water content (Kg/m3)
Hence total aggregate content = 2400 346 190 = 1864 Kg/m3
7. Fine aggregate content = Total aggregate x Proportion of fine
=1864 X 0.29 = 541 Kg/m3
8. Coarse aggregate = Total Aggregate content Fine content
= 1864 541 = 1323 kg/m3
17
7/31/2019 Coren Report 3
18/32
SUMMARY OF CALCULTIONS
Quantities Water (Kg) Fine agg.(kg) Coarse gg.(kg)
Weigth per m3 346 190 541 1323
Wt. of trial mix
Per 0.08m3
24 15.2 44 106
B. CONCRETE JETTIES
Concrete jetties are structures normally constructed at the water front as landing areas.They consist of slab deck/walkway carried by piles driver into rive r bed.
I have been involved in the design and construction of some concrete jetties for
riverine communities in Bayelsa State. These include the Dorgu Ewoama jetty in
Okoroma / Tereke Local Government area and Amasoma jetty all of Bayelsa State.
Most of the soils in the riverine areas do not have high bearing capacities, as such
Pilings are a convenient method of foundation construction for works over water such
as jetties or bridge piers.
SELECTION OF PILE TYPE AND ESTIMATION OF LENGTH
Selecting the type of pile to be used and estimating its necessary length are fairly
difficult tasks that require good engineering judgment.
Generally, piles can be divided into three categories: (a) point bearing piles, (b)
friction piles, and (c) compaction piles.
In all the jetties I designed and constructed, I ensured that piles extended down to
refusal (firm soil) so that the load is carried by either end bearing or friction or a
combination of both.
Point bearing piles are those that are extended down to the rock surface in which case,
the ultimate capacity of the piles depend entirely on the capacity of the underlying
material.
18
7/31/2019 Coren Report 3
19/32
There were cases where no layer of rock or rocklike material is present at a reasonable
depth at the site. In this circumstance point bearing piles become uneconomical;
rather the piles are driven through softer materials to specific depths.
These piles are called friction piles because most of the resistance is derived from
friction and their length depends on the shear strength of the soil, the applied load,
and the pile size.
Under certain circumstances, piles are driven in angular soils to achieve proper
compaction of soil close to the ground surface. These piles are called compaction
piles. The length of the piles depends on factors such as relative density of the soil
before compaction, desired relative density of the soil after compaction and required
depth of compaction. These piles are generally short; however, some field tests are
necessary to determine a reasonable length.
In determining the necessary length of piles, I ensure that I have a good understanding
of soil - pile interaction and good engineering judgment. It must be stated however,that, experience is very vital in the choice of pile type and lengths.
CONFIGURATION AND DESIGN OF PILES.
In positioning the piles, it was ensured that the minimum spacing of piles, centre to
centre, was not less than the pile perimeters. During design, I considered the piles as
short columns. The vertical loads on the group of the vertical piles (with symmetrical
axis) were considered to be distributed according to the equation of an eccentric loadon a pad foundation:
Pn = N/n + Nexx/Ixx Yn + Neyy/Iyy Xn
Where Pn =axial load on an individual pile
N = vertical load on the pile group
n = number of piles
exx and eyy =eccentricities of the load N about the centroidial axes xx and yy
Xn and Yn = distances of the individual pile from axes Yy and Xx respectively.
PROBLEMS ENCOUNTERED
The problems I encountered during the design and construction stages are as follows:
19
7/31/2019 Coren Report 3
20/32
i. Difficulty in obtaining soil data (index properties)
ii. Difficulty in ascertaining the actual loading on the structure. Experience has shown
that some of these jetties are used for services other than the one they were
designed for.
iii. A case of wrong reinforcement in the piles 5R12 bars used instead of 6Y12 bars
iv. Communitys divided opinion on site of project.
SOLUTIONS
i. As stated earlier, the preliminary engineering of this type of project will
necessarily involve soils survey to obtain the required geotechnical properties of
the soil. The required information included, soil stratification, bearing pressure,
shear strength and density. It was not possible to obtain this information. However,relevant texts on soils of the Niger Delta were handy from where the
characteristics of the soils were extracted. Worse conditions were used for the
design.
ii. Jetties are constructed for normal human traffic. However, in some situations, the
structure is made to carry non designed load for longer than necessary times.
In the designs I carried out, provision were made for such additional (excess) loads
on the structure. Punching shears were checked at positions where loads are likely
to be dropped. An example of this is a case of barging in a heavy duty generatingset to a community having a jetty. It is certain that the most likely off- loading
route for the set should be the jetty. Such eventual loading of jetties were
considered in the designs.
iii On one of my visits to site, I discovered that reinforcements had been provided in
all the piles. I also discovered that rather than the designed reinforcement of 6Y12
bars in each of the piles, the contractor provided for 5R12 bars .As it were, It was
not possible to pull out the reinforcement and make appropriate replacement
because it was not easy to do this without the pile driver which had left site. In
solving this problem, two things were done:
a. All the reinforcements in the piles were raised up by hand to a certain level and
1R12 bar fixed. This made the reinforcement to be six in number in each of the
piles to conform with the provision of design codes vis- a-vis minimum number of
reinforcements rods in a circular column
20
7/31/2019 Coren Report 3
21/32
b. A computation was made to determine the additional number of Y12 bars to be
added in each of the piles so as to obtain the designed steel strength, (fy).
The computation was carried out as follows:
Characteristic strength for high yield steel = 460 N/mm2
Ratio of strength of high yield steel to mild steel
= 460 : 250
= 1 : 0.54
Total No of mild steel rods provide = 6
Additional quantity of high yield rod required to obtain the characteristic strength
of high yield bar = 6 X 0.54
= 3.24 lengths
Hence No of additional Y12 bars provided = 3 lengths
iv. Most community projects are characterized by communal problems, ranging from
project site location to engagement of labour force from the community. As the
problems arose, consultations and discussions were employed in resolving the
matters. Key figures in the communities were appointed liaisons officers through
out the duration of the construction.
C. CONCRETE CULVERTS
I have undertaken the design and construction of several culverts at Risonpalm
limited, Nigeria Agip Oil Company and various parts of Port Harcourt city.
CULVERT CONFIGURATION
My selection of the most suitable culvert shape depended on such factors as
topography of site, importance of hydraulic and structural efficiency, erosion and
deposition.
In my design of culverts, I do minimize the problems of channel erosion and
deposition by choosing culvert shapes that fit the drainage channel in such a way as to
cause as little change in flow as possible. For deep, narrow channels carrying periodic
high flows, tall, comparatively narrow box or arch best fit the natural waterway.
TYPES OF CULVERTS DESGNED
i. Box culverts
21
7/31/2019 Coren Report 3
22/32
ii. Circular (Ring) culverts
BOX CULVERT: I have designed single and multiple boxes pending on the
amount of water to be discharged. The formworks are simple, inexpensive, and can
be used repeatedly. Bending and placing the reinforcement is uncomplicated and
similar to standard reinforce concrete building construction.
Box culvert: DESIGN CONSIDERATION: In my designs, I considered
box culverts best suited for moderate to low fills. As fill heights increase, they
become less economical than other shapes. They are best used for square or
rectangular openings with spans up to about 4m with height of vent rarely
exceeding 3m.
1 DESIGN PROCEDURES
In the design of culverts I adopted the following design procedures:
LOADING CASES: The loading condition I considered in the design of the
barrel (per init length of barrel) are six in number namely:
a. Concentrated vertical loads due to wheel loads
w
The reaction at foundation is assumed uniform
W (the wheel load) = PI/e
Where P = wheel load
I = impact factor
e = effective width of dispersion=Kl + w
The values of K & l depend on the dimension of the culvert
L
22
7/31/2019 Coren Report 3
23/32
ts h L = L+tw
tw tw H H = h + ts
l K = H/L (ts/tw)3
ts
b. Uniform vertical loads
w/m2
w/m2
The load and the weight of wearing coat and deck slab occur as uniform load. Thefoundation reaction is uniform.
c. Weight of walls
w w
2w
The weight of the side walls are assured to cause Uniform reaction at foundation
d. pressure from contained water
23
7/31/2019 Coren Report 3
24/32
The barrel is assumed to be full with water level at the top of the opening. A
triangular distribution of pressure is assumed
e. Triangular Lateral Loads
P/m2 P/m2
The earth pressure computed according to coulombs theory is applied to both sides.
The earth pressure is applied alone when the live load surcharge is neglected, or in
combination with case f (below), when considering live load surcharge also.
f.
p/m2 p/m2
The effect of live load surcharge when acting alone will be a uniform lateral load.
This loading is considered Uniform on both ides. When combined with case e, the
effect of trapezoidal loading will be obtained.
HYDRAULIC DESIGN
In designing of vent ways for culverts, I considered the discharge to be catered for.
Except in the case of buried barrel, the maximum flood level was always below thebottom of top slap allowing for vertical clearance. In this case, the designs of vent
way were carried out as for a culvert with reinforced concrete slab deck. The design
of vent way for buried barrel was done in a similar to a pipe culvert. The ratio of span
to height of vent I adopted in most of my designs lies between 1:1 and 1.5:1
STRUCTURAL DESIGN
24
7/31/2019 Coren Report 3
25/32
The structural designs of culverts were done using standard tables. I obtained the
governing moments, thrusts and shears at the critical sections of a box culvert from
standard tables.
In these tables, the walls and slabs are assumed to have the thickness. Moments,
thrusts and shears were computed, preferably using a tabular form for the six cases
and are algebraically added to get the net effects.
Reinforcements were provided and detailed to provide adequate resistance to the
effects of the applied forces, for the entire height. In cases were two layers of
reinforcement were required in the side walls, I considered slight reduction in the
cross section, since the compressive stress in the concrete will be reduced somewhat
by the steel in the compression zone.
Generally speaking, high localized stresses occur at corners of box culverts and other
continuous structures. I always attempt to reduce such stresses by introducing fillets at
the corners. Good practice calls for increasingly larger fillers as the spans increase, upto 150mm (measuring for the horizontal and vertical legs of the fillet) for large boxes.
The effect on the hydraulic capacity of this slight reduction in area has been found to
be insignificant.
Below is a typical cross section of a box culvert I designed on a private capacity for
use in the Port Harcourt area.
CHARACTERISTIC MATERIAL STRENGHTS
Generally, to obtain a good quality concrete in all the structures discussed above the
strength of concrete used in the design should be that below which 5% of results are
unlikely to fall. The characteristic material strengths, as these values are called, are
achieved by carrying out concrete mix designs.
This design consists of selecting the correct proportions of cement, fine and coarse
aggregates and water to produce concrete having the specified strength. Concrete
strengths I used varied from structure to structure; depending on the intended use and
exposure of the structure.
A typical concrete mix design has been carried out in chapter 3.
25
7/31/2019 Coren Report 3
26/32
KNOWLEDGE GAINED
A critical view of culverts I constructed shows that for deep, narrow channels carrying
periodic high flows, tall and comparatively narrow box or arch best fit the natural
water way.
This practice makes installation less expensive. The use of circular sections mosttimes results in maximum economy in material since for a given perimeter a circle has
a greater cross sectional area than any other shape.
26
7/31/2019 Coren Report 3
27/32
CHAPTER 4
HYDRAULICS
The content of this section is focused on some of the problems I encountered in thefield of hydraulic engineering and ways I attended to them.
2.3.1 DESIGN OF UNIFORM PIPE LINES
I undertook some designs of uniform pipe lines at Risonpalm Limited, Ubima Estate.
Only one of these cases will be discussed for the purpose of this report.
DESCRIPTION OF PROBLEM
There are two water reservoirs at the Nucleus Estate of Risonpalm Limited Ubima. A
80m3 storage tank located at the industrial area delivers water to a 250m3 over headservice tank, 2.00km away. The service tank is located at the residential area from
where water is distributed to various residential buildings.
The water line had lasted for about twenty years. The consequences of age these on
pipes were two fold:
i. Profuse leakages were noticed frequently as a result of pipe rust and consequent
rupture.
ii. No adequate supply of water in some sections of the Estate as a result ofpopulation growth, since there has been an increase in the consumption rate above
the designed value.
THE RASK
I undertook the design of a new pipe length which involved choosing the diameter
of standard commercially available PVC pressure pipes that provided the
required flow. This flow was aimed at achieving the new consumption rate.
Design Data
Length of pipeline = 2.00 Km
Minimum difference in water level between the 2 reservoirs = 20m
Effective roughness size of pipe wall (K) = 0.05mm
Population of inhabitants = 8500 persons.
27
7/31/2019 Coren Report 3
28/32
SOLUTION
Step 1: Computation of daily consumption rate
Based on the world Health organization (WHO) standard, the consumprion rate of
250 litres /head/day was used for the design.
Total consumption per day = 250 x 8500 litres
= 2.125x106 litres
Rate of consumption = 2.125x106 litres
24x60x60sec
= 24.6 litres/sec
Hence, the task is to design a Uniform pipeline to convey water at a minimum rate of24.6 l/s
Step 2: Determination (Design) of appropriate pipe size
Applying the Bernoulli equation between the two reservoirs:
H = LV2 / 2Gd + 10V2 / 2G - - - - - - -(1)
Where the figure 10v2/2g represents minor loses.
In solving this problem, the minor loses was initially ignored, hence
hf = H = LV2 / 2gD - - - - - - - - - - - - - - (ii)
Where hf = H = difference in water level between the two reservoirs
= a non-dimensional coefficient = 64/Re
Re = Reynolds number = Vd
V = Velocity of flow
D = Diameter of pipe
= Viscosity of flow material
Considering the Colebrook white equation:
28
7/31/2019 Coren Report 3
29/32
1/ = -2 log [ k/3.7D + 2.51/Re 2] - - - - - - - - - iii
Combining equations ii & iii yields
V = -2 2gD hf/L log [k/3.7D + 2.51 /D 2gd hf/L] - - - - - - iv
Using hf = 20, the corresponding discharge capacities for a serious of standard pipe
diameters were calculated and tabulated as shown below:
D (m) 0.05 0.075 0.100 0.15 0.25
V (m/s) 0.11 0.18 0.28 0.36 0.54
Q (l/s) 0.22 0.75 2.2 6.4 26.5
Thus a 250mm diameter pipeline is required since the flow rate (26.5 l/s) is close to
the required one of 24.6l/s
Checking for the effect of minor losses
Q = 26.5 m3/s V = 0.54 m/s
hm = 10v2/2g = 10 x 0.542/2x9.8 = 0.15m
hf = H hm
= 20 0.15
= 19.85m
Using this value of hf to calculate for V, yields
V = -2 2x 9.8x 0.25 x 19.85 log [0.05 2.51x4.23x10-6 ]
2000 3.7x0.25 0.25 2x9.8x0.25x19.85
2000V =-2 0.049 log (0.054)
= 0.56 m/s
The revised discharge Q = VA = 0.56 x (0.25/2)2 = 0.02748 m/s
= 27.5 l/s
This flow appears satisfactory because the minimum value required is 24.6 l/s.
29
7/31/2019 Coren Report 3
30/32
CONSTRUCTION OF PIPE LINE AND OBSERVATION
The construction of the designed pipeline was carried out in stage. The entire length
of the line had not been completed as at the time of this report. However, it was
observed that a letter distribution pattern was achieved with the extent of change
made.
2.3.2. PIPE LINE SELECTION IN PUMPING SYSTEM DESIGN :
THE PROBLEM
In Risonpalm nucleus Estate, there exists a very large effluent pit where all waste
water (including sludge) and surface run off empty into. This pit has been existing
since the inception of the company. Twenty (20) years of operation left the pit filled
with a mixture of sludge and water. During the rainy season, there is always a back
flow from this pit into the factory drains, resulting to over flooding of the premises.
The management of the company directed the engineering services department to
develop a proposal to solve the problem. As the head of the department, I carried out
the following procedures in an attempt to proffer solution to the problem.
GATHERING INFORMATION FOR DESIGN
The first step I took was to gather relevant information necessary for an adequate
design. These information are given below
Distance between pit and discharge point = 5km
Static lift = 20m
Available pump in the store had the following characteristic
Discharge (e/s) 0 10 20 30 40 50
Total head (m) 41.3 38.4 36.7 35.0 34.1 30.5
Efficiency % 40 55 62 60 58
A UPVC pipe was chosen as the transfer medium because the sewage was acidic and
may corrode steel pipes if used for the discharge.
30
7/31/2019 Coren Report 3
31/32
SOLUTION ADOPTED
The discharge rate I choosed for this system was 30 l/s.
At 30 l/s, total head =35.0m
:. Sum of the static lift and pipeline losses must not exceed 35.0m.
Pipes of different diameters were tried to achieve this condition. The appropriate
diameter is 250mm, obtained as follows
Try =D 300mm: A = 0.0707m2
V = O/A = 0.03m3/s = 0.42m/s
0.0707m
2
Re = vD/ = 0.42 X 0.3/10-6 m2/s
= 1.26 X 105
K/d = 0.15/300 = 0.0005
= 0.0345
Frictional Head loss = 0.0345 X 5000 X 0.422
0.3 X2 X 9.81
= 5.17m
Hs + Hf = 20 + 5.17 = 25.17m < 35m
This pipe diameter is too large.
Try 200mm A = 0.031m2
V = 0.03/0.031 = 6.97 m/s
Re = 0.97 X 0.2 / 10-6 = 1.94 X105
K/D = 0.15/200 = 0.00075
= 0.028
Frictional Head loss (Hf) = 0.028 X 5000 X 0.972 / 0.2 X 2 X9.81
31
7/31/2019 Coren Report 3
32/32
Hf = 33.57
Hs + Hf =20 + 33.5
= 53.57 > 35 (pipe diameter is too small)
Try D = 250mm A = 0.049
V = 0.61m3/s
Re = 0.61 X0.25 / 10-6 = 1.53 X 105
K/D = 0.15 / 250 = 0.0006
= 0.029
Hf = 0.029 X 5000 X 0.612
0.2 X 2 X 9.81
= 13.75m
Hs + Hf = 20 + 13.75
= 33.75m (