coren report 3

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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.

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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.

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(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.

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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

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S/N PROJECT TITTLE LENGTH

OF ROAD

PROJECT

COST (N)

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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

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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


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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

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(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.

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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)

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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.

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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.

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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.

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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.

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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

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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:

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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

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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.

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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:

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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

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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

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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

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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

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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

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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.

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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.

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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.

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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:

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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.

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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.

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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

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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 (

coren report 3

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