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 encou encounte ntered red,, but but a part part of a whole whole,, specif specifica ically lly presen presented ted for the purpo purpose se 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 thes thesee chap chapte ters rs pres presen ents ts the the expe experi rien ence ce gain gained ed in the the vari variou ouss fiel fields ds of Civi Civill 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 Engineerin Engineering g services services departmen department. t. My responsib responsibiliti ilities es included included design, 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 From the the year year 2000 2000 till till date date,, I have have been been work workin ing g as a Comm Commun unit ity y proj projec ectt Engine Engineer er for Niger Nigeria ia Agip Agip Oil Oil Compa Company ny (NAOC) (NAOC) Limite Limited. d. In this this capac capacity ity,, I design, estimate and oversee the construction of roads drainages, various buildings, buildings, water water scheme schemess and other other civil civil engin engineer eering ing facili facilitie tiess in NAOC NAOC’S ’S land land ownin owning g communities (Swamp and Land areas). Extracts of these experiences are put together in this document to represent a small portion of my 15 years years practice as a Civil Engineer. Engineer. 1
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 commu communit nity y projec projectt Engine Engineer, er, it is my respon responsib sibili ility ty to carryo carryout ut detai detailed led 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 found inevitable. 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 actu actual al rout routee sele select cted ed in each each situ situat atio ion n is the the one one that that repr repres esen ents ts the the best best compromise solution. The primary guiding principle adopt during route surveying includes the following: (a) (a)
The The road road shou should ld be be loca locate ted d where where it can can bes bestt meet meet the the majo majorr traff traffic ic desi desire re lines and be as directed as possible.
(b) (b)
Grad Grades es and and curv curvat atur ures es are kept kept to the mini minimu mum m nece necess ssar ary y to sati satisf sfy y the the service requirements of the highway.
(c)
Avoid Avoiding ing sudde sudden n chan changes ges in in site site dist distanc ances, es, espe especia cially lly near near jun juncti ction ons. s.
(d) (d)
Avoi Avoidi ding ng havi having ng a sharp sharp hori horizo zont ntal al curv curvee on or adjac adjacen entt to a pron pronou ounc nced ed vertical curve.
(e) (e)
Sitt Sittin ing g roads roads thro throug ugh h undev undevel elop oped ed area areass along along the the edges edges of larg largee park park lands lands and away from highly developed, expensive land areas.
(f)
Locating (as (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
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 commu communit nity y projec projectt Engine Engineer, er, it is my respon responsib sibili ility ty to carryo carryout ut detai detailed led 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 found inevitable. 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 actu actual al rout routee sele select cted ed in each each situ situat atio ion n is the the one one that that repr repres esen ents ts the the best best compromise solution. The primary guiding principle adopt during route surveying includes the following: (a) (a)
The The road road shou should ld be be loca locate ted d where where it can can bes bestt meet meet the the majo majorr traff traffic ic desi desire re lines and be as directed as possible.
(b) (b)
Grad Grades es and and curv curvat atur ures es are kept kept to the mini minimu mum m nece necess ssar ary y to sati satisf sfy y the the service requirements of the highway.
(c)
Avoid Avoiding ing sudde sudden n chan changes ges in in site site dist distanc ances, es, espe especia cially lly near near jun juncti ction ons. s.
(d) (d)
Avoi Avoidi ding ng havi having ng a sharp sharp hori horizo zont ntal al curv curvee on or adjac adjacen entt to a pron pronou ounc nced ed vertical curve.
(e) (e)
Sitt Sittin ing g roads roads thro throug ugh h undev undevel elop oped ed area areass along along the the edges edges of larg largee park park lands lands and away from highly developed, expensive land areas.
(f)
Locating (as (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
(g)
Never Never havi having ng two two road roadss inte intersec rsectin ting g near near a bend bend or at at the the top top or bottom bottom of of a hill.
(h)
For riv river er crossi crossing ngs, s, roads roads are are kep keptt at righ rightt angle angless to the the stream stream cent center er line. line.
(I) (I)
Brid Bridge gess are are not not to to be be loc locat ated ed on on or or adja adjace cent nt a high highwa way y curv curve. e.
(j) (j)
Care Care is is take taken n to avoi avoid d possi possibl blee land landsl slid ides es in in hil hilly ly ter terra rain in..
(k) (k)
To mini minimi mize ze drai draina nage ge probl problem ems, s, rout routes es are are locat located ed on high high grou ground nd in plac placee of the one a valley.
(l) (l)
As muc much h as poss possib ible le,, marsh marshes es and and othe otherr low lyi lying ng land landss subje subject ct to to floo floodi ding ng are avoided.
(m) (m)
Road Roadss are are locate located d on soil soil which which will will requ requir iree the the leas leastt pave paveme ment nt thick thickne ness ss above it. That is, the soil with high valve of CBR.
(n)
Where Where possi possible ble,, cuts cuts and and fill fillss volum volumes es are are balan balanced ced to to minim minimize ize tota totall cost 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 continued until a particular zone is narrowed down to a route location. The process involves cont contin inuo uous us sea searchi rching ng and and selec lection tion with suc such fac factors tors as: Topo opograp raphy, hy, soil/g soil/geol eolog ogica icall detail details, s, land land use, use, popula populatio tion n distri distribut bution ion,, polit politica ical, l, socia sociall and and environm environmental ental costs costs influenc influencing ing the selection selection process process at each decision making stage. Good Good reco reconn nnai aissa ssanc ncee can can be the the grea greate test st sing single le mone money y savi saving ng phas phasee in the 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 engineers of these existing civil engineering projects in the area.
3
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 and pipelines, 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 Estate Engineer for Risonpalm Ltd. (A)
FLEXIBLE PAVEMENT DESIGN & CONSTRUCTION
Below are some of the flexible pavements I designed, cost and supervised their construction
4
S/N
PROJECT TITTLE
LENGTH OF ROAD
5
PROJECT COST (N)
1
Construction of Aakor street, Omoku
900m
13,500,000
2
Construction of Iyasara street, Omoku
1.10Km
16,500,000
3
Construction Omoku
Ohali
street, 600m
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
of
police/Eze
6
9,000,000
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 “D” 7
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
(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)
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)
(Fig. 3)
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 with this 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
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
CHAPTER 2
2.0
FOUNDATION / GEOTECHNICAL ENGINEERING
A building is generally divided into two parts. The superstructure is the section above 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
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 + 1.0Q k
2.
Dead plus wind load
=
1.0G k +1.0Wk
3.
Dead plus imposed plus wind load
=
1.0G k +0.8Qk +0.8W k
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
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 non biodegradable fabrics (geotextiles), geogrids, and the like. One of Nigeria Agip Oil Company’s 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
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 flow station.
14
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 the structures 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
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 fine aggregate to coarse aggregate either by weight or by volume). A specified characteristic strength of 20 N/mm 2 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 + K s Where Fm =Target means strength Fc = specified characteristic strength K s = 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/mm 2 for Fc = 20 N/mm 2 Hence the target strength is computed as follows: 16
Fc =20 + 1.64 X 8 = 33.12 N/mm 2 . MIX DESIGN PROCESS FOR GRADE 20 CONCRETE (Fcu=20 N/mm2 )
1.
Target strength =33.12 N/mm 2.
2.
From table 2, for ordinary port land cement, crushed, the compressive strength at 28 day in 47N/mm 2, for a free water cement ratio of 0.5.
3.
From figure 3, using the compressive strength of 47N/mm 2 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/m 3
5.
Cement content
=
free - water content free – water/cement ratio
=
190/0.55 Kg/m 3
=
346 Kg/m 3
6Total aggregate content = D – W c – Wfw = Wet density of concrete (Kg/m 3)
Where D
= 2400kg/m 3 Wc
= The cement contents
(Kg/m 3)
Wfw = The free- water content (Kg/m 3) Hence total aggregate content 7.
Fine aggregate content
= 2400 – 346 – 190 = 1864 Kg/m 3 =
Total aggregate x Proportion of fine
=1864 X 0.29 = 541 Kg/m 3 8.
Coarse aggregate
= Total Aggregate content – Fine content = 1864 – 541 = 1323 kg/m 3
17
SUMMARY OF CALCULTIONS
Quantities Weigth per m3
346
Wt. of trial mix 24
Water (Kg)
Fine agg.(kg)
Coarse gg.(kg)
190
541
1323
15.2
44
106
Per 0.08m3
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
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 load on a pad foundation: Pn = N/n + N exx/Ixx Yn + Neyy/Iyy X n 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
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. Community’s 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 generating set 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
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/mm 2 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
ii.
Circular (Ring) culverts I have designed single and multiple boxes pending on the BOX CULVERT: 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. In my designs, I considered Box culvert: DESIGN CONSIDERATION: 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: The loading condition I considered in the design of the LOADING CASES: 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
ts
h
tw
L = L+t w tw
H
H = h + ts K = H/L (ts/tw) 3
l
ts
b.
Uniform vertical loads
w/m2
w/m2
The load and the weight of wearing coat and deck slab occur as uniform load. The foundation 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
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 coulomb’s 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 the bottom 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
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, up to 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
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 most times results in maximum economy in material since for a given perimeter a circle has a greater cross sectional area than any other shape.
26
CHAPTER 4 HYDRAULICS
The content of this section is focused on some of the problems I encountered in the field 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 250m 3 over head service 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 of population 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
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 = 2.125x10 6 litres
Rate of consumption
= 2.125x10 6 litres 24x60x60sec = 24.6 litres/sec
Hence, the task is to design a Uniform pipeline to convey water at a minimum rate of 24.6 l/s Step 2: Determination (Design) of appropriate pipe size
Applying the Bernoulli equation between the two reservoirs: H
=
λ
LV2 / 2Gd + 10V 2 / 2G - - - - - - -(1)
Where the figure 10v 2/2g represents minor loses. In solving this problem, the minor loses was initially ignored, hence hf
= H = λ LV2 / 2gD - - - - - - - - - - - - - - (ii)
Where hf = H
=
difference in water level between the two reservoirs
λ
=
a non-dimensional coefficient = 64/R e
R e
=
Reynold’s number = Vd υ
V
=
Velocity of flow
D
=
Diameter of pipe
υ
=
Viscosity of flow material
Considering the Colebrook white equation: 28
1/λ
=
-2 log [ k/3.7D + 2.51/Re λ 2] - - - - - - - - - iii
Combining equations ii & iii yields V
=
-2 2gD hf /L log [k/3.7D + 2.51 υ /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
hm
=
10v2/2g
hf
=
H – hm
=
20 – 0.15
=
19.85m
V =
=
0.54 m/s
10 x 0.54 2/2x9.8
=
0.15m
Using this value of h f to calculate for V, yields V
=
-2
2x 9.8x 0.25 x 19.85 log [0.05 2000
2.51x4.23x10 -6 ]
3.7x0.25 0.25 2x9.8x0.25x19.85 2000
V
=-2 =
0.049
log (0.054)
0.56 m/s
The revised discharge Q = VA = 0.56 x λ (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
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
40
55
62
60
58
Efficiency %
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
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 V = O/A
0.0707m 2
= =
0.03m 3/s = 0.42m/s 0.0707m2
=
vD/υ = 0.42 X 0.3/10 -6 m2/s
=
1.26 X 105
K/d
=
0.15/300 = 0.0005
λ
=
0.0345
=
0.0345 X 5000 X 0.42 2
Re
Frictional Head loss
0.3 X2 X 9.81 =
5.17m
=
20 + 5.17 = 25.17m < 35m
A
=
0.031m 2
V
=
0.03/0.031 = 6.97 m/s
Re
=
0.97 X 0.2 / 10 -6 = 1.94 X10 5
K/D
=
0.15/200 = 0.00075
λ
=
0.028
=
0.028 X 5000 X 0.97 2 / 0.2 X 2 X9.81
Hs + Hf This pipe diameter is too large. Try 200mm
Frictional Head loss (H f )
31
