DESIGN OF AN UNDERGROUND WATER TANK FOR GEGELE …

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DESIGN OF AN UNDERGROUND WATER TANK

FOR GEGELE COMMUNITY IN KWARA STATE

BY

AFODUN, MUHAMMAD MUKHTAR

(08/30GB017)

JULY 2013

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DESIGN OF AN UNDERGROUND WATER TANK FOR GEGELE COMMUNITY IN KWARA STATE

BY

AFODUN, Muhammad Mukhtar (08/30GB017)

DEPARTMENT OF CIVIL ENGINEERING

UNIVERSITY OF ILORIN, NIGERIA.

A Project submitted to the Department of Civil Engineering,

University of Ilorin, in partial fulfillment of the requirement for the award

Of Bachelor of Engineering Degree in Civil Engineering.

JULY 2013

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CERTIFICATION

This is to certify that this project has been read and approved as part of the requirement of

the Department of civil engineering, University of Ilorin, for the award of Bachelor of

Engineering Degree (B. Eng.) in Civil Engineering.

________________ _________________

Dr. O.G. Okeola DATE Project Supervisor

________________ _________________

Prof. Y.A. Jimoh DATE Head of Department

________________ _________________ External Examiner DATE

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DEDICATION

This project is dedicated to Almighty Allah, the All-Knowing, the All-Wise,

The Lord of the Worlds and the Master of the Day of Recompense.

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ACKNOWLEDGEMENT

My sincere gratitude goes to Almighty God for the priceless life given to me and for granting

me the grace to complete my first degree in Civil Engineering.

Due appreciation also goes to my project supervisor Dr. O. G. Okeola, for his profound

supervision, kindness, generousity, care and most importantly, for giving me the design text

on which the copious part of this project is based - Anchor, R. D. (1992), Design of Liquid

Retaining Concrete Structures, 2nd edition. Your support and contribution to my success is

indeed great.

I am extremely grateful to my parents, Alhaji and Alhaja Afodun for their unrepayable love,

guidance and care throughout my life. I also thank my siblings for their advice and prayers.

I thank the following people whose efforts and assistance has helped me in writing this

project:

Prof. Y. A. Jimoh of the Civil Engineering department, University of Ilorin, who

introduced earth retaining structures in the 400 level course work,

Dr. S. A. Raji of the Civil Engineering department, for his keen interest and his

assistance on tank safety accessories,

Engr. AbdulHamid Ayomaya of Index Consultants for his explanation of detailing

concrete structures,

Engr. Akinola of Makins consultant who made available the subsoil parameters of

the project site,

Akinola Olakunle Kenneth for his illustrative tutorials on structures,

Agboola Asimiyu, for his tutorial on Global Mapper,

Alao, Ameen and Wusu for the wonderful time we had together as fellow project

students,

I am also greatly indebted to Prof. J. A. Olorunmaiye for his fatherly concern throughout my

undergraduate years. I thank TOTAL E&P Nigeria Ltd. for the scholarship I was awarded as it

assisted me financially throughout my undergraduate study. Lastly, I thank the multitude of

people who might have helped me and are not mentioned herein.

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NOTATION

As area of steel reinforcement

c nominal concrete cover

d effective depth

fb average bond strength between concrete and steel

fct tensile strength in concrete

fcu characteristic cube strength of concrete at 28days

fs Service steel stress

fy strength of steel

H depth of liquid

Ka active earth pressure coefficient

L length of member

M bending moment

n total load per unit area, number of years

Pn Future population

Po Present population

q Distributed imposed load per unit area

r population growth rate

R Restraint Factor

smax estimated maximum crack spacing

T1 fall in Temperature from Hydration peak to ambient,

T2 Variation in temperature

v shear stress

vc critical concrete shear stress for ultimate limit state

V total shear force

wmax maximum allowable crack width

αc Coefficient of linear expansion of concrete

ɣ Density of Soil

ɣf Partial safety factor for load

ɣm Partial safety factor for material strength

ɣw Unit weight of water

ρ steel ratio

ρcrit critical steel ratio

ɸ Angle of repose, diameter of reinforcement steel

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ABSTRACT

This project is aimed at designing an underground water tank which is to be synchronized

with or to augment existing and insufficient overhead water tanks in Gegele community,

Kwara state. The project methodology involves mapping and Geo-information, survey and

siting of tank, population estimation, water demand estimation, structural analysis and

design. The design approach of the liquid retaining structure is limit state design using BS

8007 and BS8110. The design caters for strength, floatation flexural and thermal cracking.

The calculated volume of the tank needed to augment the existing overhead tanks is 600m3

and it has two compartments of 300m3 each. The wall, roof slab and floor slab thicknesses

are 350mm, 250mm and 400mm respectively. Provision of reinforcement in walls: vertical

bars: T20 @ 175mm c/c Each Face (1800mm2), horizontal bars: T20 @ 175mm c/c Each Face

(1800mm2), floor slab: Top face- T25 @150 c/c Top Face Shortspan, T25 @175 c/c Top Face

longspan, Bottom face- T20 @ 100 c/c Each Way Bottom face, top Slab: T16 @150 c/c both

faces. It is expected that the Underground water reservoir will improve water accessibility

and distribution in Gegele community. The structure is designed to meet stability, strength

and serviceability requirements as stated by BS8007 and BS8110.

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TABLE OF CONTENTS

Title page i

Certification iii

Dedication iv

Acknowledgement v

Notations vi

Abstract vii

Table of Contents viii

List of Tables xi

List of Figures xii

CHAPTER ONE: INTRODUCTION 1

1.0 Introduction 1

1.1 Problem Statement 1

1.2 Aim and Objectives 2

1.3 Justification 2

1.4 Scope of Work 2

1.5 Description of Study Area 3

CHAPTER TWO: LITERATURE REVIEW 6

2.0 Introduction 6

2.1 Water Demand 6

2.1.1 Introduction 6

2.1.2 Population Forecast 7

2.1.3 Arithmetical progression of population 7

2.1.4 Water Demand 7

2.2 Types of Water Tanks 8

2.3 Objectives of Structural Design 11

2.4 Fundamental Design Methods 11

2.5 Impermeability 11

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2.6 Site Conditions 12

2.7 Tension, compression and flexural resistance of walls 12

2.8 Exposure classification 13

2.9 Structural Layout 14

2.10 Joints in Liquid retaining structures 14

2.11 Civil Engineering Standard Method of Measurement (CESMM) 16

2.11.1 Preparation of Bill of quantities 17

2.11.2 Project Cost Estimation 18

2.12 Review of past works 18

CHAPTER THREE: METHODOLOGY 20

3.1 Preliminary Studies 20

3.1.1 Mapping and Geo-information 20

3.1.2 Survey and Siting of Tank 20

3.2 Population Estimation 21

3.2.1 Average Population per building 21

3.2.2 Future population Estimation 21

3.3 Tank sizing 21

3.3.1 Water demand estimation 21

3.4 Structural analysis and Design 23

3.4.1 Limit State Design 23

3.4.2 Ultimate limit state 23

3.4.3 Serviceability limit state 23

3.5 Loading 23

3.6 Wall thickness 23

3.6.1 Ease of construction 24

3.6.2 Structural arrangement 24

3.6.3 Adequate strength in shear 24

3.6.4 Cracking due to tensile forces 25

3.7 Floatation 25

3.8 Rate of Materials 25

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3.9 Design of Underground Tank 26

3.10 Structural Drawings and detailing 47

3.11 Bar bending schedules 56

3.12 Bill of Engineering Measurement and Evaluation. 58

3.12.1 Quantity of Materials 58

CHAPTER FOUR: CONCLUSION AND RECOMMENDATION 62

4.1 Conclusion. 62

4.2 Recommendations 62

References 63

APPENDIX 65

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LIST OF FIGURES

Figure Title Page

1.1 Aerial Photograph of Gegele community showing the location of the existing insufficient overhead tanks and the location of the proposed underground tank. Source: Google Earth

4

1.2 Map of Kwara State showing its constituent local Governments

5

1.3 Map of Nigeria showing Kwara State. 5

2.1 tension and compression in a cylindrical tank 13

2.2 Walls of a rectangular tank 13

2.3 complete contraction joint 15

2.4 partial Contraction joint 15

2.5 Expansion joint 16

2.6 Sliding joint 16

3.1 Image of digitalized buildings using global mapper (Buildings are easier

to count in this image as compared to satellite imagery).

22

3.2 Plan view of tank 48

3.3 Sectional Elevation of Tank 48

3.4 Top Slab detailing 49

3.5 Floor Slab Detailing 50

3.6 Walls D&E detailing 51

3.7 Wall A Detailing 52

3.8 Cross sectional Elevation showing reinforcements 53

3.9 Sectional Side Elevation 54

3.10 Access plan detailing 55

3.11 Sectional elevation of access showing detailing 55

3.12 3D model of Tank 56

B.1(b) Bending Moment Coefficient for walls 66

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LIST OF TABLES

Table Title Page

3.1 Approximate minimum thickness of R. C. Cantilever wall subjected

to water pressure

24

3.2 Roof slab Bar Bending schedules 57

3.3 Floor slab Bar Bending schedules 57

3.4 Wall D&E Bar Bending schedules 57

3.5 Wall A Bar Bending schedules 58

3.6 Access Bar Bending schedules 58

3.7 Reinforcement quantities of various members 60

3.8 BEME of Construction Materials (Labour and profit overhead of 25%

is included)

61

C.1 Sectional Areas per metre width for various bar spacing 66

3.14 Bending moment Coefficients for rectangular panels 67

A2.3 Limiting Moments tables 68



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CHAPTER ONE: INTRODUCTION

1.0 Introduction

The necessity to store and supply purified water has been a major source of civil engineering

activity for many civilizations (Ian and Roger, 1991). The growing need for water tanks was

impelled by climate change, water scarcity and rapid population explosion within the last

decade. Climate change has a major effect on the amount of water flowing in rivers and has

strained the level of water stored in the water supply reservoirs.

Underground tanks are liquid containing vessels that accommodate the internal pressure

from the containing fluid and the lateral earth pressure from the surrounding soil.

Underground water tanks are used to store water, petroleum products and similar liquids.

The force analysis of the tanks is about the same irrespective of the chemical nature of the

content. All tanks are designed as crack free and water proof structures to eliminate any

leakage to the soil and also to prevent seepage into the tank there by causing contamination

(Sahoo, 2008).

Water is one of the basic necessities for a human being. Different sectors of the society use

water for different purposes, for example drinking, cooking, bathing, and washing clothes

and sanitation. Water requirements for a society varies upon factors such as number of

buildings in the society, number of floors in each building, number of flats on each floor, etc.

swimming, gardening have become additional factors for increased water demand

nowadays (Gupta, 2010).

1.1. Problem Statement

The Nigeria water sector is faced with a lot of challenges which have made the sector

perform below expectations. Of these problems is lack of adequate infrastructure for water

storage and distribution. For quality water to be made available for all, water distribution

infrastructures like underground and overhead tanks water tanks must be placed in every

community to meet daily water demand at a relatively low cost and with ease.

Gegele is a community that has a problem of poor water supply and distribution and it has

also been faced with a problem of low pressure water from the supply mains in the past,

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though this problem no longer exists. The supply is also erratic, which calls for water storage

to cater for peak and off-peak demand. Gegele community is usually supplied by 12

municipal overhead water tanks about a year ago. However, the number has been reduced

to 4. The overhead tanks are situated near the Ilorin Central mosque. The numbers of the

tanks were reduced due to concern over the aesthetics of the newly rehabilitated mosque.

1.2 Aim and Objectives.

The aim of this project is to design for a durable, reliable, economic and functional

underground water tank for Gegele community in Kwara State. The specific objectives to

accomplish the aim are:

Estimation of water demand for Gegele community.

Structural analysis of underground water tanks.

Economic design and detailing of the concrete underground water tank.

Carry out BEME for the designed tank.

1.3 Justification.

Water is one of the basic necessities for human survival and making it available for

consumption requires infrastructures like underground tanks. Nigeria is a country that

needs to invest more in water supply and distribution infrastructures to be able to achieve

the millennium development goals (MDG). Therefore the justification of this project is to

improve water supply and distribution by the optimum synchronization of an underground

water reservoir with the existing distribution network.

1.4 Scope of Work

The scope of the project will be limited to the design of an underground tank for Gegele

community in Kwara State to augment the existing overhead tanks. The general idea is to

collect and store water from the supply mains in the proposed underground tank and then

distribute it to Gegele community under gravity. The Northern and higher part of Gegele can

be supplied water from the existing overhead tanks efficiently through pipe isolation.

However, this project does not detail the technique of pipe isolation. The design approach

of the liquid retaining structure is limit state design under BS 8007 and BS8110.

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1.5 Description of Study Area

The study area is Gegele community situated within Ilorin West Local Government Area. It is

an urban settlement in the heart of Ilorin metropolis of Kwara State (see Figures 1.1, 1.2 and

1.3). Gegele has a global coordinate of 8° 29ʹ 41.89ʺ N and 4° 32 ʹ 53.24ʺ E. Gegele is grossly

populated by indigenes though most commercial activities are along the major roads. The

gradient is relatively high with elevations of 318m in the northern part to 310 m in the

Southern part.

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Figure 1.2: Map of Kwara State showing local Government of the study area (hatched)

Figure1.3: Map of Nigeria showing Kwara State

(Source: upload.wikimedia.org/Wikipedia/commons/8/82/Nigeria_Kwara_State_map.png)

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Chapter Two: Literature Review

2.0 Introduction

The water supply facility for each person must be continuous and sufficient for personal and

domestic uses. Domestic uses ordinarily include drinking, personal sanitation, washing of

clothes, food preparation and personal and household hygiene. According to the World

Health Organization (WHO), between 50 and 100 litres of water per person per day are

needed to ensure that most basic needs are met and few health concerns arise. The water

required for personal or domestic use must be safe, therefore free from micro-organisms,

chemical substances and radiological hazards that constitute a threat to health. Measures of

drinking-water safety are usually defined by national and local standards. WHO’s Guidelines

for drinking-water quality provide a basis for the development of national standards that, if

properly implemented, will ensure the safety of drinking-water (United Nations, 2010).

Factors such as Population explosion, Expansion of business activity, Rapid urbanization,

Climate change, Depletion of aquifers have caused increasing demand for water.

Water resources are sources of water that are useful or potentially useful. Uses of water

include agricultural, domestic, industrial etc. Virtually all of these human uses require fresh

water. 97% of the water on the Earth is salt water. However, only three percent is fresh

water; slightly over two thirds of this is frozen in glaciers and polar icecaps. The remaining

unfrozen fresh water is found mainly as groundwater, with only a small fraction present

above ground or in the air. Nigeria is blessed with abundant water resources which have not

been adequately harnessed. Water resources development evolved with the urbanization

that followed the advent of western form of administration that tended to concentrate

efforts on large scale programme by creation of artificial lakes and emphasis later on

boreholes in areas removed from the man-made lakes. (Fagoyinbo, 1998)

2.1 Water Demand

2.1.1 Introduction

According to World Health Organization (WHO) the average consumption for every human

being to have access to sufficient water for personal and domestic use is between 0.05 and

0.1 cubic metre of water per day (United Nations, 2010). In a recent study by Sule et. al.,

http://en.wikipedia.org/wiki/Fresh_water




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(2010), it was found out that most Ilorin residents use between 0.046 to 0.115 cubic metre

of water per person per day. Before designing proper water works project, it is essential to

determine the quantity of water that is required daily. This involves the determination of

the following items.

2.1.2 Population Forecast

There are several methods for population forecast, these include:

1. Arithmetic progression method

2. Geometrical progression method

3. Incremental increase method

4 Decreased rate of growth method

2.1.3 Arithmetical progression

This method population forecast, gives lower results. In this method the increase in

population from decade to decade is assumed constant. This method should be used for

forecasting population of large cities which have reached their saturation population.

(Punmia et. al.,1995). Generally, water supply projects are designed for a design period of

20 to 40 years after their completion. The population at the end of the design period would

be used to design the tank capacity. Mathematically,

rategrowthpopulationr

yearsofNumbern

populationInitialP

yearsatPopulationP

Where,

Eqn(3.1) nr)(1PP

0

n

0n

n

2.1.4 Water Demand

An average person may consume no more than 5to 8 litres a day in liquid and solid foods,

including 3 to 6 litres in the form of water, milk and other beverages. However, the per

capita consumption of water drawn from public supply is quite large (Punmia et. al., 1995).

Total water requirements may be divided into five categories some of the categories are:

1. Residential or domestic use

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The residential or domestic use includes water requirements for drinking, cooking, bathing,

washing of clothes, utensils and house, and flushing of water closets. Provision is sometimes

made for domestic animals. According to World Health Organization (WHO) the average

consumption for every human being to have access to sufficient water for personal and

domestic use is between 0.05 and 0.1 cubic metre of water per day (United Nations, 2010).

2. Water systems losses

Losses from a water distribution system consist of (Punmia et. al., 1995):

i. Leakage and overflow from service reservoirs

ii. Leakage from main and service pipe connections

iii. Leakage and losses on consumer’s premises when they get unmetered household

supplies

iv. Under-registration of supply meters

v. Large leakage or wastage from public taps.

Losses in supply lines are mainly due to defective pipe joints , cracked pipes, and loose valve

and fittings.

2.2 Types of Water Tanks

A water tank is used to store water to tide over the daily requirements. In general, there are

three types of water tanks:

(i) Surface tanks

(ii) Elevated tanks, and

(iii) Underground tanks.

Water tanks could also be made from ranges of materials such as (Woolhether, 2012):

1. Plastic: A plastic underground water tank is lightweight, easy to handle and easy to

install. Plastic water tanks present no health risks. Water can be kept fresh and

uncontaminated for long periods. Plastic tanks are used in many countries where

fresh water is scarce. In Nigeria, for instance, plastic tanks are used to store

rainwater for drinking purposes. Other areas may use the stored water for

agricultural needs such as irrigation or for watering livestock.

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2. Concrete: Precast or cast-in-place concrete is an exceptionally strong and durable

material used for underground water tanks. Concrete tanks are built to withstand

the gases and chemicals emitted from the soil. Underground concrete tanks work

well where space is a challenge. Concrete works especially well in fire-prone areas. If

placed underground, there is minimal risk of damage from fire or environmental

factors.

3. Fiberglass: Underground water tanks made of Fiberglas are lightweight and versatile.

They are durable and are not susceptible to corrosion or leakage. Fiberglas tanks are

less expensive than steel or concrete. Installation is much simpler and less time-

consuming. Fiberglass underground water tanks can safely store fresh water for

short- or long-term use.

4. Steel: Underground water tanks can be constructed of carbon steel, lined carbon

steel or stainless steel. These steel tanks receive a corrosion resistant polyurethane

coating. Steel tanks are considered safe and contamination-free for storing potable

or non-potable water. They come in a variety of shapes and sizes for both

commercial and residential use.

From the shape point of view, water tanks may be of several types, such as:

1. Circular tanks

2. Rectangular tanks

3. Spherical tanks

4. Circular tanks with conical bottoms (Intze tanks).

5. Conical tanks

Rectangular tanks are usually used when small capacity or volume of water is required. For

small capacities circular tanks prove uneconomical as the shuttering (formwork) for circular

tank is very costly. The rectangular tanks should be preferably square in plan so as to

economize construction material. It is desirable that the longer side should not be greater

than twice the smaller side (Mohammed, 2011).

However rectangular tanks are not used for large capacities since they are not economical

and also, its exact analysis is difficult. For a given capacity perimeter is least for a circular

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tank (Punmia et al, 2003). The choices of concrete as the material for constructing the

underground water tank have many advantages over other materials, including: (Gibson

2010)

Inherent strength making them naturally rigid and durable.

Durability with no danger of rusting, corroding or being damaged by tree roots.

Availability in a variety of different sizes.

Concrete tanks are not liable to ‘float’ like a plastic tank may under high Hydrostatic

pressure.

Concrete is made from natural materials and is therefore easily recycled.

Concrete tanks save space by being buried underground.

Keeping water cool.

In the construction of concrete structures for the storage of liquids, the imperviousness of

concrete is an important basic requirement. Hence, the design of such construction is based

on avoidance of cracking in the concrete. In addition, concrete tanks require low

maintenance. Concrete construction makes for a substantial, sturdy tank structure that

easily contain the internal liquid pressure while comfortably resisting external forces such as

earthquake, wind, and lateral earth pressure. The water tank has to be far away from

sanitary structures such as soak-away and septic tanks.

Since the capacity of the tank is likely to be large, it would be economical to use a cylindrical

shape for the tank; otherwise a rectangular tank is preferred. The dimension, capacity or

volume of the tank will be determined by multiplying the standard average consumption of

water per person multiplied by the population of the community.

When tanks are situated underground, the walls of the tank are to be designed for earth

pressure as well as water pressure acting separately, and also acting simultaneously.

Similarly the floors of the tank are to be designed for hydrostatic water pressure (if water

table is higher) acting upwards. The walls of underground tanks are designed for earth

pressure, especially when the tank is empty. Such a condition is very frequently experienced

as and when the tank is emptied for cleaning purposes. The active earth pressure, which

varies triangularly along the depth of tank wall, depends upon the conditions of side fill. If

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the water table rises up to ground, or even up to the level above the tank, additional

hydrostatic pressure due to subsoil water will be experienced (Punmia et al, 2003)

2.3 Objectives of Structural Design

A structure that is designed to retain liquids must fulfill the requirements for normal

structures in having adequate strength, durability, and freedom from excessive cracking or

deflection. In addition, it must be designed so that the liquid does not percolate or leak

through the concrete structure. In the design of liquid retaining structures, if the structure

has been proportioned and reinforced to be leak-proof, then the strength is more than

adequate. The requirements for ensuring a reasonable service life for the structure without

undue maintenance are more onerous for liquid retaining structures than for normal

structures, and adequate concrete cover is also essential. Equally the concrete itself must be

of good quality and well compacted (Anchor, 1992).

2.4 Fundamental Design Methods

Historically, the design of structural concrete has been based on elastic theory with

specified maximum design stresses in the materials at working loads. More recently limit

state philosophy has been introduced providing a more logical basis for determining factors

of safety. In limit state design, the working or characteristic loads are enhanced by being

multiplied by a partial safety factor (Anchor, 1992).

Formerly, the design of liquid-retaining structures was based on the use of elastic design

with material stresses so low that no flexural tensile cracks developed. This led to the use of

thick concrete sections with copious quantities of mild steel reinforcement. The probability

of shrinkage and thermal cracking was not dealt with on a satisfactory basis, and nominal

quantities of reinforcement were specified in most code of practice (Anchor, 1992).

2.5 Impermeability

Concrete for liquid retaining structures must have low permeability. This is necessary to

prevent leakage through concrete and also to provide adequate durability, resistance to

frost damage and protection against corrosion for reinforcement and other embedded steel.

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The minimum thickness of concrete for satisfactory performance in most structures is

200mm (Anchor, 1992).

Liquids loss may occur at joints that have been badly designed or constructed and also at

cracks. It is however found that cracks of limited width do not allow liquid to leak and the

problem for the designer is therefore to design the structure so that surface crack widths

are limited to a predetermined size (Anchor, 1992).

2.6 Site Conditions

The choice of site for a reservoir or tank is usually dictated by requirements outside the

structural designer’s responsibility, but the soil conditions may significantly affect the

design. A well-drained site with under lying soils having a uniform bearing pressure at

foundation level is ideal. A high level ground water must be considered in designing the

tanks in order to prevent flotation and poor bearing capacity may give rise to increased

settlement (Anchor, 1992).

The soil investigation must also include chemical tests on the soils and ground water to

detect the presence of sulphates or other chemicals in the ground which could attack the

concrete and eventually cause corrosion of the reinforcement (Anchor, 1992).

2.7 Tension, compression and flexural resistance of walls

Generally, there are two fundamental ways in which the pressures subjected to the tank can

be contained:

1. By forces of direct tension and compression (Fig 2.1).

2. By flexural resistance (Fig 2.2).

Anchor (1992) explained that structures designed using tensile or compressive forces are

normally circular and may be prestressed. Rectangular tanks rely on the flexural action using

cantilever walls, propped cantilever walls, or walls spanning in two directions.

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Figure2.1: tension and compression in a cylindrical tank (Source: Anchor, 1992)

Figure2.2: Walls of a rectangular tank (Source: Anchor, 1992)

2.8 Exposure classification

Structural concrete elements are exposed to varying types of environmental conditions. The

roof of a pump house is waterproofed with asphalt or roofing felt and, apart from a short

period during construction, is never exposed to wet or damp conditions. The lower section

of the walls of a reservoir are always wet (except for brief periods during maintenance), but

the upper sections may be alternately wet and dry as the water level rises. The underside of

the roof of a closed reservoir is damp from condensation (Anchor, 1992).

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Precautions should be taken to ensure that moisture and air do not penetrate to the

reinforcement and cause corrosion which in turn will cause the concrete surface to spall.

Adequate durability can be ensured by providing a dense well-compacted concrete mix with

a concrete cover of 40mm, but it is also necessary to control cracking in the concrete and

prevent percolation of liquid through the member (Anchor, 1992).

Presently, the faces of liquid retaining structure are designed for a crack width of 0.2mm or

0.1 mm in some members where appearance is very important. Previous designed used

different exposure classes A, B and C for various faces under different situations. The Code

of practice for Design of concrete structures for retaining aqueous liquids (BS 8007) requires

that all liquid-retaining structures should be designed for at least “severe conditions of

exposure.

2.9 Structural Layout

Generally, assuming member sizes precede any form of detailed analysis of the structure.

Generally, structural design should be considered from the viewpoints of strength,

serviceability, ease of construction and cost. In liquid-retaining structures, it is particularly

necessary to avoid sudden changes in section since they cause concentration of stress and

hence increase the possibility of cracking (Anchor, 1992).

It is a good principle to carry the structural loads as directly as possible to the foundation,

using the fewest structural members. It is preferable to design cantilever walls as tapering

slabs rather than as counterfort walls with slabs and beams (Anchor, 1992).

2.10 Joints in Liquid retaining structures

1. Contraction Joint

It is a movement joint with deliberate discontinuity without initial gap between the concrete

on either side of the joint. The purpose of this joint is to accommodate contraction of the

concrete (Sahoo, 2008). The joint is shown in Fig.2.3.

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Fig 2.3 complete contraction joint (Source: Sahoo, 2008)

A contraction joint may be either complete contraction joint or partial contraction joint. A

complete contraction joint is one in which both steel and concrete are interrupted and a

partial contraction joint is one in which only the concrete is interrupted, the reinforcing

steel running through (Sahoo, 2008) as shown in Fig.2.4

Fig 2.4 partial Contraction joint (Source: Sahoo, 2008)

2. Expansion Joint

It is a joint with complete discontinuity in both reinforcing steel and concrete and it is to

accommodate either expansion or contraction of the structure. A typical expansion joint is

shown in Fig.2.5

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Fig 2.5 Expansion joint (Source: Sahoo, 2008)

This type of joint requires the provision of an initial gap between the adjoining parts of a

structure which by closing or opening accommodates the expansion or contraction of the

structure.

3. Sliding Joint

It is a joint with complete discontinuity in both reinforcement and concrete and with special

provision to facilitate movement in plane of the joint. This type of joint is provided between

wall and floor in some cylindrical tank designs (Sahoo, 2008). A typical joint is shown in

Fig.2.6

Fig 2.6 Sliding joint (Source: Sahoo, 2008)

2.11 Civil Engineering Standard Method of Measurement (CESMM)

The main purpose the Bill of Quantities is to assist the contractors to produce an accurate

tender figure efficiently and to enable post contract administration be carried out in an

efficient and cost effective manner. Estimation is the process of pricing based on the

~ 17 ~

available information, specification, and various drawings toward arriving at total sum

known as tender sum. This is to be done within the context of form of contract and terms in

which the sum will apply or may vary (Okeola, 2012).

2.11.1 Preparation of Bill of quantities

The phrase ‘Bills of Quantities’ is more appropriate to a building contract where the General

Summary contains a list of individual Bills. In civil engineering documents the equivalent Bills

are called Parts so the overall document is a Bill of Quantities. The pre-contract exercise of

measuring the work also applies to the post-contract task of measurement. The correct

term for this task is re-measurement where the work is physically measured on site or

admeasurement where the actual quantities are calculated from records (Okeola, 2012).

There are five sections in the Bill of Quantities:

1. Preamble

2. List of Principal Quantities

3. Day work Schedule

4. Work Items (divided into parts)

5. Grand Summary

1. Preamble

The Preamble is an extremely important section of the Bill of Quantities and is the

potentially vital source of information to the estimator. If any other Methods of

Measurement have been used in the preparation of the Bill of Quantities, the fact should be

recorded there (Okeola, 2012).

2. Preliminaries

The preliminaries section of the bill of quantities is the engineer or QS’s introduction to the

contract. The section provides information on the location, size, and complexity of the

project and gives details of the conditions of contract under which the project is to be

implemented (Okeola, 2012).

~ 18 ~

3. Coding and numbering

The aim of the coding is to produce a uniformity of presentation to assist the needs of

the estimator and the post-contract administration.

2.11.2 Project Cost Estimation

There are many approaches to preliminary estimates of proposed projects. They all use

some measures of gross unit costs from recently completed construction works which are

updated by the use of factors which recognizes cost differences as a result of time frame,

location or any peculiarities of the work that is being estimated. However in general the

estimating structure comprises (Okeola, 2012):

Dividing the project into small elements so as to allow a single rate or unit cost to be

applied to each element

Extending the quantities and rates to determine a cost for each element

Summing the resulting elemental costs and

Applying indirect costs to give a complete estimate.

2.12 Review of past works

Mohammed (2011) stated that the design of a tank can be more economical, reliable and

simple if optimization method is used to calculate the minimum cost of structural design of

rectangular and circular sanitary concrete tanks.

A brief theory behind design of liquid retaining structure (circular water tank with flexible

and rigid base and underground water tank) using working stress method was presented by

Sahoo (2008) as a final year project. The study also included computer subroutines to

analyze and design circular water tank with flexible and rigid base and rectangular

underground water tank. The programme was written in Microsoft excel using visual basic

programming language.

Fagbemi (2011) worked on the analysis and design of an elevated water tank to meet the

daily water demands of Tanke Akata and Tanke Iledu areas of Ilorin, Kwara State. A

concrete- Intz tank was the type of tank chosen for design from economical and capacity

~ 19 ~

point of view, the design approach was elastic design method. The project also highlighted

water demand and use.

Gupta (2010) analyzed the theory behind the design of liquid retaining structure such as

rectangular underground water tank. The report also included design requirements of water

tank, survey, excavation methods, reduced levels, average depth of UGWT, soil on which it

is constructed, depth of water table, type of mix design and capacity of the tank. The tank

was designed for Gyanganga society which is a residential settlement.

~ 20 ~

CHAPTER 3: METHODOLOGY

The methodological steps involved in executing the project are outlined below:

3.1 Preliminary Studies

The Preliminary studies are findings which are paramount to the structure to be designed.

The preliminary studies are:

3.1.1 Mapping and Geo-information

Google earth software was used to show location of catchment by aerial photographs. This

software also states the elevation of various points above sea level. For effective and

efficient distribution the tank’s proposed location is the highest in the area, with an

elevation of 319m above sea level. The elevation of the area reduces outward from the

location. The location of the existing overhead tank is about 10m away. For maximum water

pressure during distribution the buildings closer to the tank will be supplied from the

overhead tank while buildings farther away and of lower elevation will be supplied by the

Underground tank.

3.1.2 Survey and Siting of Tank

The survey was to establish the number and capacity of overhead water tanks. Four

overhead cylindrical steel overhead tanks stacked on steel stanchions exist but only three of

the tanks serve Gegele community. The parameters of the overhead tanks are:

Number of tanks = 4

Number of tanks serving Gegele = 3

Length of tank= 6.4m

Diameter of tank=3.048m

Volume of each tank=46.72m3

Total volume of tanks= 46.72m3x3 =140.16m3

Survey also shows that proposed tank location is well drained and not sunken. The tank is

sited far away from sewage and septic tanks to prevent contamination and on a soil with

good Bearing capacity. The site is also of high altitude so that effective pressure for efficient

distribution can be generated.

~ 21 ~

3.2 Population Estimation

3.2.1 Average Population per building

Global Mapper was used to digitalize the satellite imagery (fig 3.1) of Google Earth, the

digitalized imagery eases building count which is used in calculating the population of the

catchment. The average population per building was estimated from a sample. From a

research carried out by Sule et Al. most building in the medium density area of Ilorin have a

population of 5-8 people per building.

3.2.2 Future population Estimation

people7398

0.025))(204932(1P

2.5%r

Years20n

people4932P

Eqn(3.1) nr)(1PPformula, rategrowth ArithmetictheUsing


yearsofNumbern

.populationInitialP

years.20atPopulationP

years20ofperiodafordesignedisStructure

2.5%NigeriaofrategrowthPopulation

n

0

0n

0

n

3.3 Tank sizing

3.3.1 Water demand estimation

Population estimate for Gegele community, arithmetic population growth rate of 2.5% and

WHO per capita water demand was used to estimate the size and geometry of the tank for a

20-year design period.

~ 22 ~

Figure3.1: Image of digitized buildings using global mapper (Buildings are easier to count in

this image as compared to satellite imagery).

~ 23 ~

3.4 Structural analysis and Design

The tank was designed and detailed to BS 8007 & 8110 using limit state design approach.

Lateral earth pressure, hydrostatic and surcharge pressures are analyzed in depth. Design

caters for strength, flotation, tensile, flexural and thermal cracking.

3.4.1 Limit State Design

Limit state design of an Engineering structure ensures that structure is safe, durable and

serviceable. In this method of design working loads are multiplied by partial factors of safety

and the material strength are divided by further partial factors of safety.

3.4.2 Ultimate limit state

This limit state satisfies strength, (i.e strength of the structure against collapse or failure.)

3.4.3 Serviceability limit state

Serviceability limit state controls of excessive deflections and crack widths when structure is

under service loads. Serviceability limit state ensures that structure is serviceable under

loads. Serviceability also ensures a structure is fire resistant. Generally, in liquid retaining

structures when the serviceability is satisfied, then strength would also have been satisfied

3.5 Loading

Liquid retaining structures are subjected to external earth pressure due to surcharge and

soil excluded. The internal loads are due the retained liquid, in this case the liquid retained

is water with an approximated density of 10 KN/m3. There are two most critical loading

cases for the external walls of the reservoir: when tank is full and when tank is empty. When

the tank is full with water, the passive resistance of the soil is neglected. Also when tank is

empty, only the lateral earth pressure is to be considered. For internal walls dividing a tank

into compartments, the most critical loading case is when a compartment is full while

another is empty. A partial factor of safety of 1.4 is used for all dead loads, water pressure

and lateral earth pressure.

3.6 Wall thickness

The main factors which affect optimum wall thickness are

1. Ease of Construction.

~ 24 ~

2. Structural arrangement.

3. Adequate strength in shear.

4. Avoidance of excessive crack width.

3.6.1 Ease of construction

300mm is the minimum wall thickness for four layers of reinforcement as required by liquid

retaining structures to have appropriate concrete cover and to be properly compacted to

prevent leaks.

3.6.2 Structural arrangement

A cantilever retaining wall requires a thicker section at the base because it is only restrained

at one edge which has high bending moment and shear forces. A rectangular panel spanning

in two directions and restrained on all edges retaining the same height of liquid will require

lesser wall thickness. If a cantilever wall is to be used to retain a 5m head of water a 700mm

thick wall would be required at the base, which would taper to 300mm at the top, but if a

two way spanning slab is used the required thickness may just be 350mm, as used in this

design (see Table 3.3).

Table 3.1: Approximate minimum thickness of R. C. Cantilever wall subjected to water pressure

(Source: Anchor, 1992)

Height of wall (m) Minimum wall thickness h (mm)

8 800

6 700

4 450

2 250

3.6.3 Adequate strength in shear

The check for strength in shear certifies if the assumed wall thickness can withstand the

critical shear stress; the point of maximum shear is the base of the wall assuming the wall is

a cantilever. The critical shear stress is given by (Anchor, 1992):

3.2) Eqn(

400100

2579,0

4

1

3

1

3

1

m

dbd

Asfcu

Vc

bd

As100=0.5%

~ 25 ~

fcu =35N/mm2

m =1.25

d -effective depth

Shear stress on the section, )3.3(Eqn bd

Vv u

Section thickness is adequate if v< vc

3.6.4 Cracking due to tensile forces

Structural tensile forces occur in rectangular tanks due to applied internal pressures, usually

in combination with flexure (Anchor, 1992). The additional provision of steel to cater for

tensile forces in walls is given by:

)4.3(Eqn 2 s

SF

TA

Where T is the tensile force.

3.7 Floatation

The check for floatation is critical before the design of the wall reservoir floor slab, because

the two methods for tackling floatation depend on the floor slab thickness or its extensions

at the side. The ground water level of the site is assumed to be the average of water level in

neighbouring wells. The average is water level of 3.5m from the ground level. Floatation

check is deemed OK when the weight of the empty tank is more than the weight of ground

water displaced. The factor of safety varies between 1.1 and 1.25 (Anchor, 1992).

3.8 Rate of Materials

The contract rate and direct labour rate for conctete, excavation, reinforcement, and other

materials used were given by Physical Planning Unit (PPU), University of Ilorin. The following

price quotations were given by the PPU (2013):

Concrete (1:1 ½:3) , 35N/mm2: 35000/ m3

Steel reinforcement: 280/ Kg

Sawn Form Work: 1150/ m2

75mm Blinding (1:3:6): 1800/ m2

Polythene sheet (1000g): 225/ m2

Excavation: 1750/ m3

Granite spread for covering roof: 9540/ m3

~ 26 ~

3.9 DESIGN OF UNDERGROUND TANK

~ 27 ~

DESIGN INFORMATION

Hypothetical Client: Ilorin West Local Government, Kwara state. Designed by: AFODUN, M. M

UNDERGROUND WATER TANK Intended use of structure

1. BS8007: Design of concrete structures for retaining aqueous liquids.

2. BS8110: The structural use of concrete. 3. Design of Liquid retaining concrete structures by Anchor

Relevant codes of Practice and design manuals

Allowable Bearing pressure =250KN/m2 Ground water level =3.5m below GL Angle of repose, ɸ = 300 Density of Soil = 18KN/m3

Subsoil conditions

Self-weight of concrete =24KN/m3 Surcharge on roof =5.0 KN/m2 Surcharge on soil due to vehicles =10 KN/m2 Unit weight of water, ɣw =10KN/m3 Partial factor of safety for loads =1.4 Partial factor at serviceability =1.0

General Loading conditions

Characteristic strength of steel, Grade of ribbed high-yield bars, fy (main bars and links) =460 N/mm2 Characteristic strength of concrete, fcu =35N/mm2 Concrete grade =Grade 35A

Material strength

Severe Concrete cover, c = 40mm maximum allowable crack width, wmax =0.2mm

Exposure condition

Variation in temperature, T2 =200C fall in Temperature from Hydration peak to ambient, T1 =300C Coefficient of linear expansion of concrete, αc =12 Restraint Factor, R = 0.5 population growth rate, r =2.5%

Other important parameters

~ 28 ~

REFERENCE CALCULATION OUTPUT

Population survey Google earth 2013 Wikipedia, 2013 Punmia et. Al., 1995 Punmia et. Al., 1995 W.H.O. Sule.et. Al., 2010

TANK OVERHEADEXISTING OF VOLUME

533

072.07398

Demand Water Capitaper Population DemandWater

0.072mareapopulatedDenselyfordemandwaterAverage

m0.1150.046residents

IlorinofdayperdemandwatercapitaperAverage

m0.10.05dayperdemandwatercapitaperAverage

DEMANDWATER

people7398

0.025))(204932(1P

2.5%r

Years20n

people4932P

nr)(1PPformula, rategrowth ArithmetictheUsing


yearsofNumbern

.populationInitialP

years.20atPopulationP

years20ofperiodafordesignedisStructure

2.5%NigeriainrategrowthPopulation

people4932

41112communitytheinpeopleofNumberTotal

411communitytheinHousesofNumber

people12buildingainpeopleofNumberverage

ESTIMATIONPOPULATION

3

3

3

3

n

0

0n

0

n

m

A

Population= 4932 people Design Population= 7398 people Per capita water demand= 0.072m3

~ 29 ~


Recce Survey

3

2

2

72.46

4.6524.17

22

cylinder a of volume

1.524mradiusr

3.048mdiameterd

6.4mlength l

m

hr

demand water CapitaPer V

perioddesign yr. 20 afor building ain people of NoP

VP

Volume Totalbuildings ofNumber

:forcater tank willoverhead thebuildings ofnumber thegCalculatin

140.16m

46.72 3Volume Water Total

exist. tank thisof numbers Three

PC

PB

PCPB

3

people 12 population Initial P

population Future P

years 20years ofnumber n

2.5%rategrowth population

:

)1(PP

formula rategrowth Population arithmetic theUsing

0

n

0n

r

where

nr

Buildings 108

0.07518

140.16 for cater tank willoverhead thebuilding ofnumber The

18

)100

5.2201(12

peopleP

P

n

n

392840

84.392

16.140533

Tank overhead of Volume-Demand Water Total

Tank nd Undergrouof Volume

TANK ND UNDERGROUOF VOLUME

3

litres

m

Volume of each

overhead tank=46.72m3

No of buildings overhead tank will cater for: 108 buildings

~ 30 ~


side.shorter thee than twicmore benot

should sidelonger ther tanks,rectangula ofdesign EconomicFor

ts.compartmen twointo divided is tank the

available, becan overboardan that so 400m ofTank afor Designing

TANK OFNG DIMENSIONI

3

33 400397m256.36.3Volume m

capacity. bearing optimum with soil aon sited also is tank The

altitude.high relatively of also is site tank The

ion.contaminat

prevent to tanksseptic and sewage fromfar sited is tank The

TANK OFSITING

0.5m of board free a has tank The

TANK ND UNDERGROUTHE OF DESIGN STRUCTURAL

KN/m Capacity Bearing

30repose of Angle

/18Density Soil

PROPERTIES SOIL

2

o

3

mKN

~ 31 ~


All dimensions are in millimeters.

2

3

2

2

/87.2

1.028.7KN/mroofon aggregate Stone ofWeight

KN/m 10soil retainedon vehiclesloaded todue Surcharge -

slab. roof on the KN/m 2.0 of load liveA -

LOADING

mKN

m

assumedis

70m).(say joint expansion an

require ch wouldlength whi than theless is structure theof size The-

STRUCTURE. OF LAYOUT

3

2

0

3

10KN/m water ofdensity Assume

1.35m i.e

depth theof 0.75m of head water ground aon based be shouldDesign

/63

118Pressure Soil

3

1

30sin1

30sin1

30

/18 density, soil

sin1

sin1 t,coefficien PressureEarth Active

pressure Soil

Loads (a)

S.ASSUMPTION DESIGN

mKN

K

mKN

K

K

a

a

a

Surcharge on soil= 2.87KN/m2

~ 32 ~


460 grade bars yieldhigh ribbed-steelent Reinforcem

concrete. finished

of Kg/m 325 ofcontent cement mininum a35A with grade Concrete

Materials (c)

0.2mmh crack widtDesign

exposure. severefor Design

BS8110 and 8007 BS Design to (b)

3

structure. monolithic a as designed be willstructure The

. leakage of sources potential are they as

desirable are jointsmpovement no structure, theof size theof In view

Joints (f)

panels. spanning way two

continuous as designed are panel slab roof and wallfloor, All

(e)Design

40mm steel oflayer outer cover to (d)

pressures. surcharge and water ground soil, External

WELLS)(BOTH EMPTY WELLS(a)

CASESLOADING

~ 33 ~


BS 8007 2.3

diagrams pressure theseCombining

6.67H)H3

1-(110

: thereforeis water ground of presence the todue

load extra effective The effect.buoyancy the todue reduced is

soil theofdensity effective epresent th is water ground Where

in well water todue Pressure

full Wet well(b)

soil. external theof

resistance pressure for the made be willallowance No

~ 34 ~


BS8110 BS8110 Table 3.9

2

4

1

3

13

1

c

4

1

3

1

3

1

c

/60.0

25.1

300

4005.0

25

3579.0

v

d. depth, effective

300mm, of thicknessminimum aFor

0.5% be toassumed is100

400100

2579.0

v

:isnt reiforceme of 0.5% assumed

an with concrete grade 35 ofStrength Shear Ultimateallowable The

300mm. be should

thicknessminimum thehigh wall, 5m a ofon Constructi of EaseFor

Sections of Thickness

mmN

bd

A

dbd

Af

s

m

scu

mKN /121533.375.301.252

1530

2

14.1

8

5

:diagram pressure thefrom forces theofaddition The

:is loading external maximum

the todue walls theoffoot at the forceshear ultimate maximum The

Soil Water Surcharge

thick.400mmfloor and thick 350mm wallsUse

5.270

40165.12202

2d thicknessoverall

67.20110006.0

10121

bv

Vd

shear,for required wallofdepth effective minimum The

3

mm

c

mm

ondistributi

Walls, h=350mm floor, h=400mm

~ 35 ~


SLAB) (ROOF SLAB COVER TOP

for. designed be need oneonly so similar, are slabsBoth

1l

65.6l

supports. itsover slab spanningway - twocontinuous a is slab roof The

free.partially assumed are walls theand roof ebetween th joints The

y

y

x

x

l

ml

~ 36 ~


thick250mm slab a Using

:sizing Slab

2

kk

2

2

23

2

KN/m 20.42

1.6(5.0)1.4(8.87)

1.6QG 1.4n Load,Design

/0.5 on trafficconstructilight and excluded) are (vehicles

roofon access partial toodue load Live

/87.8 load dead Total

/87.20.1m28.7KN/mcracking) thermalreduce (to

aggregates stone ofWeight

6.0KN/m 240.25slab roof of Weight Self

Loading Slab

mKN

mKN

mKN

2

y

2

x

2

sy

2

sx

M

M Moments,Support

M

M Moments,Span Maximum

:tsCoefficienMoment Bending

xy

xx

xsy

xsx

nl

nl

nl

nl

KNm

KNm

KNm

KNm

0Medges,Shortspan

93.3765.642.20042.0Mmidspan,Shortspan

.38.5265.642.20058.0Medges,Longspan

73.3965.642.20044.0Mmidspan,Longspan

x

2

sx

2

y

2

sy

202

2

1640250

2shortspan ofdirection In

steel.diameter 16mm of use theAssuming

entReinforcemMain

mm

chd

ent.reinforcemn comoressiofor need no 156.0

026.0202100035

1093.37

93.37Mmoment,midspan Shortspan

2

6

2

sx

k

bdf

Mk

KNm

cu

Roof slab d=200mm

Gk=8.87KN/m2 Qk=5.0KN/m2

n=20.42KN/m2

Msy= 39.73KNm

My= -52.38KNm

Msx= 37.93KNm

K=0.026

~ 37 ~


Table A2.3 (Anchor, 1992)

20295.0

95.0

9.0

026.025.05.0

9.025.05.0

z

la

la

kla

ladz

strength. saitsfiesent that reinforcem minimum theis this

)(566mm B c/c Y12@200mm provide

89.49320295.046087.0

1093.37

87.0

2

26

mmladf

MA

y

s

)(1340mm B c/c 150mm @ Y16 Provide

KNm 37.93 Moment

52mm barsmain cover to

250h ickness,Section th

0.2mmhcrack widt

statelimit lity serviceabi gConsiderin

2

mm

KN/m 144 capacityshear Ultimate

N/mm 186stresses steel Service

KNm 41.7moment Limiting

2

29.0120

FS-4770.55MF

4603

2FS

26slab way -2 of Ratiodepth Span Basic

SLAB ROOF FORCHECK DEFLECTION

bd

M

providedA

requiredA

s

s

52226MF ratio basicdepth effective

span limiting

293.09.0120

113.02-4770.55MF

93.02021000

1093.37

02.1131340

89.493460

3

2FS

2

6

2

bd

M

Provide Y12 @200mm c/c B (566mm2)

Provide Y16 @ 150mm c/c B (1340mm2) E F

~ 38 ~


Table 5.2-Anchor Table 5.1- Anchor

OK. Deflection ratio,span Actualratiospan limiting

9.32202

6650

depth effective

span actual

0.5R factor,Restraint

12concrete ofexpansion linear oft coefficien

0.2mmhcrack widtDesign

20T ture,in temperaVariation

30T ambient, peak toHydration from turein tempera fall

13.65m3)(0.352)(6.3

onconstructi continuous of Maximum

ENTREINFORCEM MINIMUM OF NCALCULATIO

c

0

2

0

1

C

C

.1111

4

2

12

3

2

3

2

2

111110180

2.0

0.2mmhcrack widt allowable Maximum

nmicrostrai 18030125.0

strainn contractio effectiveNet

max

max

max

max

6max

1

mmS

S

S

f

f

f

fSAlso

mmTR

wS

TR

b

ct

b

ct

c

c

%35.0100460

6.1

%36.01001111

4

y

ctcrit

f

fAlso

faceEach )(905mm c/c 125mm @ T12 Provide

900

25010000.36%

lengthunit per area0.36%entreinforcem of area Minimum

slab. roof For the

2

2mm

Deflection OK

Provide T12@ 125mm c/c For distribution

~ 39 ~


)(1340mm facesboth for c/c @150mm T16 provide

1260mm

3501000100

36.0

0.36%

entreinforcem of area minimum

wallsFor the

2

2

Area

WALLSON FORCES

5300mm

350mm) of thicknessbase a (assuming 2

250

2

3505000

slabfloor toslab roof of centre tocentre walls,ofheight Effective

pressures. soil

equivalent by the pressure surcharge therelace toconvenient isIt

pressure. surcharge toduerly rectangula and pressures,

soil and water toduerly triangulaloaded are panels wallsThe

5.87mheight equivalenth

5.87mx

34.38

x

31.05

5.3

approach; ianglessimilar tr usingBy

~ 40 ~


Anchor, 1992 Pg. 90 Appendix B Case 2 Fig B.1

2

2

/533.510 Hpressure water Internal

2 CASE

44.38KN/m total

10.00 1.56.67H6.67r Groundwate

34.38surcharge) ncludingpressure(i soil External

1 CASE

Loading

mKN

faceloadedontensionM

faceunloadedontensionM

SpanHorizontalM

spanverticalM

H

v

30.130.5

65.6

l

l ratio

6.65m walloflength

5.3m wallofheight

A Wall

z

x

70.1565.638.44008.0

25.3965.638.4402.0

47.233.587.538.44017.0

5.633.587.538.44046.0

EMPTY)(TANK WATERSOIL

CASE1

2

2

H

H

V

v

M

M

M

M

70.1565.653008.0

88.4665.65302.0

31.253.553017.0

48.683.553046.0

FULL)(TANK WATERINTERNAL

CASE2

2

2

2

2

H

H

V

v

M

M

M

M

face.each on A, Wall2 Case As

emptyother thefull,t compartmen One :1

3.130.5

65.6

l

l

30.5l wallofHeight

650.6l wallofLength

B Wall

z

x

z

x

CASE

ratio

m

m

~ 41 ~


3.13.5

65.6

65.6l wallofLength

30.5l wallofHeight

D Wall

A WallasJust :C Wall

x

z

z

x

l

lratio

m

m

A Wallas sam :G F, E, Walls

A Wall2 Case as Same

FULL)(TANK WATERINTERNAL1, CASE

A Wall1 Case as Same

EMPTY)(TANK WATERAND SOIL 1, CASE

below. evaluated is which wallsin the tension cause both wellsin

water todue load The ignored. bemay and low is stress ecompressiv

theof valueThe n.compressioin concrete by the resisted arewhich

wallsin the forces horizontal ecompressiv cause loads External All

FORCES DIRECT

2

2

/482

4.3)(5.310

wallofheight 1mlowest over the pressure water Average

KN/m 535.310pressure water Maximum

B. andA on walls pressure todue D in WallTension

D WALLIN TENSION

mKN

23

2

S

25.3312402

10159

2

/240F of stress steel service a Assuming

ve.conservati isit but neglected isfloor theofeffect The

1592

319.2F and D on Wallheight metreper Force

height 319.2KN/m6.6548Force Total

mmF

TA

mmN

KN

S

s

~ 42 ~


KN00.4182Load Total

917.28KN 713.650.4024SlabFloor .4

KN8.793)24535.03.6(3C B, A, Walls

1146.6KN 24)50.352(13.65G F, E, D, Walls3.

751.98KN 713.655)(2.87liveload and aggregate Stone

roofon load 2.Imposed

KN 573.3 713.650.2524 weight self 1.Roof

:loads theanalyzing andt compartmen a Taking

structure.

theof weight imposed the todue slabisfloor under the pressure soil The

SLAB FLOOR

/66.65765.13

41825.1

Area Base

LoadFOSpressure Bearing

:is pressure soil the

area,floor over theon distributi uniform Assuming

2mKN

.floatationfor checked be tohas structure base, thedesigning Before

other. for the providing andt compartmrn one of base for the Designing

3430.98KN weight Total

917.28KNslabFloor

793.8KN C B, A, Walls

1146.6KN G F, E, D, Walls

KN 573.3 weightself Roof

:empty tank ofWeight

~ 43 ~


BS8110 Table 3.14 CASE 9

satisfied. Floatation

waterground todueUplift empty tank ofWeight

274525.1

65.3545

Safety ofFactor

empty tank ofWeight

3.186395.1765.1310displaced water ofWeight

WATERGROUND TO DUE UPLIFT

KN

KN

slab. way twoa is SlabFloor

16650

6650

l

lSlab,Floor For the

x

y

KNm

KNm

60.16265.666.65056.0M

7.15965.666.65055.0M

later moments fixingfor allowing and supportedsimply Assuming

2

y

2

x

KNm

KN

KN

32.328

wlE WallformMoment

85.565.137

65.6535.0224C Wallfrom UDL

85.565.137

65.6535.0224E Wallfrom UDL

surcharge neglecting wallsfrom moments fixing minimum

2

KNm

KNm

28.13032.3260.162MMax

54.1432

32.327.159MMax

(Internal) B Wall

y

x

Floatation check Satisfied

~ 44 ~


300mm10-20-40-400laverinner ofdepth Effective

40mmcover

400mmknessFloor thic

ENTREINFORCEM FLOOR

)TF(2810mm c/c 175mm @ T25 Use

28.130M

)TF(3270mm c/c 150mm @ T25 Use

54.143M

2

y

2

x

KNm

KNm

FLOOR IN STEEL MINIMUM

0.5R factor,Restraint

12concrete ofexpansion linear oft coefficien

0.2mmhcrack widtDesign

20T ture,in temperaVariation

30T ambient, peak toHydration from turein tempera fall

c

0

2

0

1

C

C

FLOOR: T25@150 TF T25@175 TF

~ 45 ~


.1111

3

25

2

25

3

2

3

2

2

25

111110180

2.0spacingcrack

0.2mmhcrack widt allowable Maximum

nmicrostrai 18030125.0

strainn contractio effectiveNet

max

max

max

max

6max

1

mmS

S

S

f

f

f

fSAlso

mm

mmTR

wS

TR

b

ct

b

ct

c

c

%35.0100460

6.1

%75.010031111

25

y

ctcrit

f

fAlso

2

s 3000mm40010000.75%A

)(3140mmEW TF c/c @100mm T20 Provide

Face Bottom

)(2810mmlongspan TF c/c @175mm T25 Provide

)(3270mmshortspan TF c/c @150mm T25 Provide

Face Top

slabfloor for t arrangemen steel Final

2

2

2

40mmCover

350mm thicknessWall

ENTSREINFORCEM WALL

mm286121240350

:entreinforcem oflayer inner deth to Effective

70.6KNmMoment

c/c T16@150mmfor A2.6 Table A,Appendix toRefering

)(1340mm faceeach for c/c T16@150mm

:earlieris calculatedent reinforcem minimum The

2

T20 @100 EW

~ 46 ~


2

s 1340A c/c mm 150 @ T16 use bendingfor Therefore

70.6KNm/m. than less are moments All

Steel Horizontal

A WALL

mm

)(1800mm EF c/c 175mm @ T20 Provide

25.1671mm25.331mm 1340

:siondirect tenfor cater toareaent reinforcem theAdding

2

222 mm

ent.reinforcem same with theprovided areG F, E, D, C, B, Walls

KNm/m 80.8Moment Allowable

EF. c/c 175mm @ T20 Provide

68.48KNm/mMoment Vertical Maximum

Steel Vertical

T20 @175 EF For all walls. T20 @175 EF For all walls.

~ 47 ~

3.10 STRUCTURAL DRAWINGS AND

DETAILING

~ 48 ~

Fig3.2: Plan view of tank

Fig 3.3: Sectional Elevation of Tank

~ 49 ~

Fig

3.4

: To

p S

lab

det

ailin

g

~ 50 ~

Fig

3.5

: Flo

or

Slab

Det

ailin

g

~ 51 ~

Fig

3.6

: Wal

ls D

&E

det

ailin

g

~ 52 ~

Fig3.7: Wall A Detailing

~ 53 ~

Fig

3.8

: Cro

ss s

ecti

on

al E

leva

tio

n s

ho

win

g re

info

rcem

ents

SEC

TIO

N A

- A

~ 54 ~

SECTION B-B

Fig 3.9 Sectional Side Elevation

~ 55 ~

Fig 3.10 Access plan detailing

Fig 3.11: Sectional elevation of access showing detailing

Section C-C

~ 56 ~

Fig 3.12: 3D model of tank

~ 57 ~

3.11 BAR BENDING SCHEDULES

Table 3.2: Roof slab Bar Bending schedules

Table 3.3: Floor slab Bar Bending schedules

Table 3.4: Wall D&E Bar Bending schedules

~ 58 ~

Table 3.5 Wall A Bar Bending schedules

Table 3.6 Access Bar Bending schedules`

~ 59 ~

3.12 BILL OF ENGINEERING MEASUREMENT AND EVALUATION.

3.12.1 QUANTITY OF MATERIALS

Concrete (1:1 ½:3)

Roof Slab: Volume= (length × breadth × thickness)-Access = (13.65m×7m×0.25m)-(2×1.0m×1.0m×0.25m) = 23.89m3-0.5m3 = 23.39m3

Walls A, B and C: Volume=number × length × height × thickness =3 × 6.3m × 5m × 0.35m =33.08m3 Walls D, E, F and G: Volume=number × length × height × thickness =2 × 13.65m × 5m × 0.35m =47.78m3 Floor Slab: Volume=length × width × thickness =14.25m × 7.6m × 0.4m =43.32m3

Access: Volume=number × length × breadth × height

=8×1.1m×0.2m×0.2m =0.352m3

Total volume of concrete=147.93m3

Excavation: Volume=length × breadth × height

=16.25m × 9.6m × 5.48m =854.88m3

Blinding (1:3:6): Volume=length × breadth × thickness

=14.25m × 9.6m × 0.075m =10.26m3

Granite spread: Volume=length × breadth × thickness

=13.65m × 7m × 0.1m =9.56m3

Formwork: Area=length × breadth Roof slab = 12.6m × 6.3m=79.38m2

~ 60 ~

Floor Slab= 2× (14m×0.4m) + 2 × (7.6m×0.4m) = 17.28m2 Wall A =

Internal (6.3m×5.0m ) = 31.5m2 External (7.0m×5.25m) = 36.75m2

Wall B= (6.3m×5.0m) × 2= 63m2

Wall C= Internal (6.3m×5.0m) =31.5m2

External (7.0m×5.25m) = 36.75m2

Wall D, E, F and G Internal=4×5.0m×6.3m=126m2 External=2×5.25m×13.65m=143.33m2

Total area: 565.49 m2 Polythene sheet (1000g):

Area= length × breadth

=14.25m x 7.6m

=108.3m2 Reinforcement:

Table 3.7: Reinforcement quantities of various members

S/N Member Weight=0.006165ɸ2 (kg) Number of similar member

Total weight (Kg)

1 Wall A 4196 3 12588 2 Wall D&E 5559 2 11118 3 Roof slab 3140 1 3140 4 Access 109 2 218 5 Bottom slab 11510 1 11510 Total Weight 38574

~ 61 ~

Table 3.8: BEME of Construction Materials (Labour and profit overhead of 25% is included)

S/N Description Quantity Unit Rate(N) Amount(N)

A Preliminaries 250000

B Excavation

1 Excavation to floor slab base level not exceeding 5.5m

854.88 m3 1750 1496040

Sub Total 1496040

C Concrete

1 Provide, mix and place grade 25 concrete(1:3:6) for 75mm Blinding

10.26 m2 1800 18468

2 Provide, mix and place Concrete grade 35 for floor, walls and roof (1:1 ½:3), 35N/mm2

147.93 m3 35000 5177550

Sub Total 5196018

D Formwork

1 Sawn Formwork for all floor, walls and roof

565.49 m2 1150 650314

Sub Total 650314

E Polythene Sheet

1 Polythene sheet (1000g) 108.3 m2 225 24368

Subtotal 24368

F Reinforcement

1 Steel reinforcement for floor, walls and roof of tank according to specification.

38574 Kg 280 10800720

Subtotal 10800720

G Granite

7 Granite spread for covering roof 9.56 m3 9540 91203

Subtotal 91203

H Total Amount 18508663

I Add 2% VAT 370174

J Add 5% Contingency 925434

K GRAND TOTAL 19804270

~ 62 ~

CHAPTER FOUR: CONCLUSION AND RECOMMENDATION

4.1 Conclusion.

The designed underground water reservoir will help store daily water requirements instead

of depending on the direct erratic supply form mains. Storing water in tanks for domestic

household use is very important because of great demand during peak periods. The tank

was designed using limit state design approach. The structure is designed to meet stability,

strength and serviceability requirements as stated by BS8007 and BS8110.

4.2 Recommendations

1. It is recommended that a computer program should be written to design the tank to

make accurate and faster analysis.

2. The structure should be built as designed in this report so as to improve water

availability and accessibility in all households in Gegele community.

3. After construction the structure should be maintained for long useful life.

4. Vehicular movement should be restricted on the roof slab by barb wires.

~ 63 ~

References

Anchor, R. D. (1992). Design of Liquid Retaining Concrete Structures. 2nd edition. Edward

Arnold, London, UK.

British Standards, BS 8007 (1987), Code of Practice for Design of Concrete Structures for retaining

aqueous liquids.

British Standards, BS 8110 (1987), Code of Practice for Design of Concrete Structures.

Fagbemi, O. S. (2011). Analysis and design of elevated water tank, Final Year Project,

Department of Civil Engineering, University of Ilorin, Ilorin, Nigeria.

Fagoyinbo, J. B. (1998). Improvement in Water Resources Capacity Utilization Towards the

achievement of Objectives of Vision 2010. Proceedings of the National Engineering

Conference and Annual General Meeting, Nigerian Society of Engineers, Maiduguri, Nigeria.

Pp 17

Gibson. C, (2010). Concrete Underground Water Tanks. Available at:

http://www.homeimprovementpages.com.au/article/concrete_underground_water_tanks

(Accessed October 30, 2012).

Gupta, L. (2010). Design of Underground Water Tank. Final Year Project. Department of Civil

Engineering, Walchand Institute of Technology, Solapur, India.

Ian, B. and Roger, W, (1991). Design Tables for Water retaining structures, Longman group,

UK Ltd.

Karamouz, M., Szidarovsky, M. and Zahraie, B. (2003), Water Resources Systems Analysis,

Lewis Publishers, Washington DC, USA.

Mohammed, H. J. (2011). Economical Design of Water Concrete Tanks. European Journal of

Scientific Research. (49)4, pp 510-520.

Okeola, O. (2012) Civil Engineering Practice. A monograph on the basic Civil Engineering

Practice. Department of Civil Engineering, University of Ilorin, Ilorin, Nigeria.

http://www.homeimprovementpages.com.au/articles/author/craig_gibson

~ 64 ~

Physical Planning Unit, University of Ilorin (2013), Personal Communication with the Chief

Quantity Surveyor, Physical Planning Unit, University of Ilorin, Nigeria.

Punmia, B. C., Jain. A. K. and Jain. A. K, (1995). Environmental Engineering-1: Water Supply

Engineering. Laxmi Publications (P) Limited, New Delhi, India. Vol. 1 pg. 139-162.

Punmia, B. C., Jain. A. K. and Jain. A. K, (2003) Reinforced Concrete Structures. Laxmi

Publications (P) Limited, New Delhi, India. Vol 2 pg 261-262.

Sahoo, N. (2008). Design of water tank. Final Year Project. Department of Civil Engineering,

National Institute of Rourkella, India.

Sule, B.F., Ayanshola, A.M. and Salami, A.W. (2010). Water Consumption Patterns in Ilorin,

Kwara State, Nigeria. Proceeding of the 2nd Annual Civil Engineering Conference, University

of Ilorin, Nigeria, 26 – 28 July 2010 Department of Civil Engineering, University of Ilorin,

Ilorin, Nigeria. Pg. 231.

United Nations (2010). Media brief: The Human Right to Water and Sanitation. Available at:

www.un.org/waterforlifedecade (Accessed: December 9, 2012).

Woolhether. L. (2012). The Best Underground Water Tanks. Available at:

http://www.ehow.com/list_7502181_underground-water-tanks.html#ixzz2BJrZ1BbJ

(Accessed: November 5, 2012).

http://www.ehow.com/list_7502181_underground-water-tanks.html#ixzz2BJrZ1BbJ

~ 65 ~

APPENDIX

~ 66 ~

Table C.1 (source: Anchor, 1992)

Figure B.1(b) Bending Moment Coefficient for walls. (source: Anchor, 1992)

~ 67 ~

Table 3.14 (BS 8110; 1987)

~ 68 ~

(Source: Anchor, 1992)

~ 69 ~

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