OPTIMUM DESIGN OF WATER INTAKE TOWER FOR AN EARTH DAM

ABSTRACT

Water  intake  towers  are  typically  tall,  hollow,  reinforced  concrete  structures  and  form entrance to reservoir outlet works. It is observed that most dam intakes in Nigeria are not functional due to no way to monitor assets. In this work, the best type of tower was selected and the optimum design of the water intake tower was designed using Random Finite Element Method (RFEM) to analyses according to British standard specification (BS5059, BS8110; part 1, 2 and 3 and BS5337). The materials were utilized taking into account durability factors, actions of forces on the structure were analysed taking special attention to the geometry and type of water intake tower which was selected taking into consideration the best for a particular geometry (rectangular and circular). The design contains rectangular water intake tower which has an area of 1610 mm2, a thermal cracking of 0.039 mm < 0.2 mm, ratio of 0.0033 < 0.0053 and a minimum steel area of 500 mm2, the dam height of 6 m has thickness of concrete wall of 0.20 m, varied of the dam height (6 m, 10 m, 15 m and 20 m) corresponding thickness of concrete wall (0.20 m, 0.35 m, 0.50 m and 0.65 m), corresponding area of steel (1085 mm2, 1899 mm2, 2712 mm2 and 3525 mm2), corresponding uplift pressure (117.6,  196,  294  and  392)  and  corresponding  maximum  horizontal  pressure  (176.4, 490,1102.5 and 1960) respectively.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background to the Study

Hydrology is a subject of great importance to human and the environment, which deals with all phases of the water on earth (Chow et al., 1988). Hydrology has many practical uses such as in the design and operation of hydraulic structure, water supply, wastewater, irrigation, flood control, erosion and sediment control, pollution abatement, recreational and so on (McCuen, 2017). Generally, hydrology science offers guidance for planning and management of water resources and geography principles that are important for the study of hydrology (Davie, 2002). A structure  placed  in  a  water  source  to  permit  the  withdrawal  of  water from   the   source   and discharge it into an intake conduit through which it flows to the treatment plant is called intake. Intakes consist of two sections First, intake conduit with the screen at the inlet end and valve to control the flow of water. Second, a structure permitting the withdrawal of water from source and housing and supporting intake conduit, valves, pumps etc. The structure may be of stone masonry or brick masonry, Reinforced cement concrete, or concrete blocks, the structure is constructed watertight and is designed to resist all forces likely to come upon it including the pressures due to water, wave action, the wind, floating debris, annual rainfall, geological formations.

It acts as an entrance structure and conducts the flood into the deviation system, also it acts as intake tower when utilization by installation and construction of ducts, valves and lower discharger. Intake towers are mostly concrete and high constructions with some valves for water discharge, most of these structures have a control room to adjust and discharge the water   of   reservoir   for   public   services   such   as   drinking   water,   electricity   power production, helping to the reservoir discharge in case of emergency and permission to the lake water level reduction for specific inspection and maintenance. Intake towers can be located inside or at contacting with concrete dams body or outside the dams (USACE, 2003).

Intake function is to provide clam and still water, free from floating matter for water supply schemes. Its main purpose is to provide clam and still water conditions so that comparatively pure water may be conveniently collected from the source. Reservoirs are readily classified in accordance with their primary purpose for example, irrigation, water supply, hydroelectric power generation, river regulation and flood control. Dams are of numerous types, and type classification is sometimes less clearly defined, an initial broad classification into two generic groups can be made in terms of the principal construction material employed (Novak et al., 2007).

Intake towers are typically tall, hollow reinforced concrete structures and form entrance to reservoir outlet works. They often house equipment for regulating the release of impounded water  for  vital  public  services  such  as  water  supply  or  generation  of  electricity,  aid  in emptying the reservoir in an emergency condition, and permit reservoir lowering for inspections and special repairs. Intake structures can be located within or attached to concrete gravity dams or located outside the dam (Goyal and Chopra, 1989).

Water from the rivers is always drawn from the upstream side, because it is free from the contamination caused by the disposal of sewage in it. The water enters in the lower portion of the intake known as sump-well from penstocks, the penstocks are fitted with screens to check the entry of floating solids and are placed on the downstream side so that water free from most of the suspended solids may only enter the jack-well, the water from the sump-well of the intake to upper portion of the intake. Number of penstock openings is provided in the intake tower to admit water at different levels, the opening and closing of penstock valves is done with  the help  of wheels  provided  at  the pump-house floor.  In  such  cases  reservoirs  are constructed by constructing  weirs  or dams  across the rivers, the water which  enters  the vertical pipe is taken to the other side of the dam by means of an outlet pipe. At the top of the water intake tower sluice valves are provided to control the flow of water (Novak et al., 2007).

Some rivers have too much variation in their discharge of monsoon and dry season. If in dry weather  the  water  level  falls  below  the  lowest  penstock  of  the  intake  well,  a  weir  is constructed across the width of the river to raise the water level and maintaining some storage of water for dry period. In the case of shallow and broad rivers an approach channel is constructed, so that sufficient quantity of water may reach the intake even in dry period, this is known as wet intake tower. Another typical type of intake well, which can equally be used for collecting water from river or reservoir, it is commonly known as dry intake tower. The entry of water through the ports is controlled by the cylinder gates operated from the top, by means of wheels (Goyal and Chopra, 1989).

When there is no water inside the withdrawal conduit, the dry intake will be subjected to greater buoyancy force. Hence, the structure of this intake should be more massive than the wet intake, the water from the desired depth of the river of reservoir can be collected by opening the desired port. In case of emergency and temporary works, movable intakes can be used. In this type of intake pumping plant is installed in a carriage or trolley and the suction pipe having strainer pipe at the end is lowered in the water. The water is directly pumped from the river and sent for the treatment and distribution (Novak et al., 2007).

Each design is unique and may take on many forms and variations, the intake structures can be separated into two broad categories: freestanding and inclined. Selection of the appropriate type depends on a number of considerations including site conditions, economics, and effectiveness in  meeting project  requirements.  Project requirements  can include reservoir operating range, drawdown frequency, discharge range, trash conditions and required frequency of intake cleaning, reservoir ice conditions, water quality and temperature operating requirements, and environmental requirements such as fish passage (Novak et al., 2007).

Models are constructed to serve as proof of an idealized logical structure and they are an important element of methodical theories (Adem, 2005). A model is an expression to show a part of the natural or human created world which can be in the form of a physical, analog or mathematical model (Dingman, 2002). As a simple definition for models, a physical model is defined as a scaled-down form of a real system (Salarpour et al., 2011). The analog model is the result of a simulated process that is used to represent a natural process. Mathematical models, on the other hand, include clear chronological set of relation, numerical and logical steps that change numerical inputs into numerical outputs. Today, mathematical models are more preferred due to the rapid development of computer technology.

1.2 Statement of the Research Problem

A dam is a structure built across a stream or river to hold water back. Dams can be used to store water, control flooding, and generate electricity. Unfortunately, they also worsen the impact of climate change. They release greenhouse gases, destroy carbon sinks in wetlands and oceans, deprive ecosystems of nutrients, destroy habitats, increase sea levels, waste water and displace poor communities. Consequently, for these reasons, priority has always been given to the construction of dams throughout last decades; many communities are in need of water during the dry season and which most of our Dams are not functional due to one reason or the other. Therefore, farmers and water resources personnel need to focus attention on the management of this vital resource by making the right choice of what and when to manage the water crisis. Different types of hydraulic gates and hoists, working on different principles and mechanism are in use for controlled release of water through spillways, sluices, intakes, regulators, ducts and tunnels. It is essential to be aware of the different factors, which would largely affect the choice of gates and intake tower and would help in the selection.

The dynamic response of an intake tower may present quite complex characteristics due to many factors. The water, inside and outside of the tower, plays an important role in the modification of the response of the structure, the behavior of the structure to the loading is very important considering the various benefits of the intake towers (Goyal and Chopra, 1989). Projecting a structure, besides the usual concerns with safety and functionality, there is also the issue of durability. The structure needs to guarantee those for a determined period of time or the project would not be economic and sustainable. Therefore, there are norms that determine some parameters that should be met so the required durability is provided. Usually the design is made taking into account a 50 year minimum lifespan for the structure, but in certain cases such as hard to repair structures or important projects, the minimum lifespan should be widened for 100 years (Mago and Chamra, 2009). Modelling and analysis of intake towers requires sound understanding of the behavior due to the complexities involved. The intake tower having axis symmetric geometry and being submerged in an unbounded reservoir necessitates a 3-dimensional model for accurate analysis. It is important to incorporate fluid- structure-interaction and the effect of unbounded reservoir condition while carrying out analysis (Oogatho, 2006).

Therefore, the need for the optimum design of an intake tower to divert flow laterally in order to prevent downstream flood and minimize erosion, others have design different towers and functional ones are few, it is the main aim of this research, the tower will be check for critical situation and the parameter will be determine, the change of height and its effects using Random Finite Element Method (RFEM) structural analysis.

1.3 Aim and Objectives of the Study

The aim of this study is for the optimum design of water intake tower, for an Earth Dam. Objectives of the study are to:

i.   identify the types of water intake tower for an earth dam;

ii.  design of water intake tower using a program RFEM;

iii. determine the effect of geometry on the shape of water intake tower.

1.4 Scope of the Study

This research focuses on the hydraulic design of a water intake tower. The design is based on analyzing the flood frequency in the area and using RFEM structure analysis program to design  and  to  estimate  the  best  discharge  for  an  Intake Tower.  The  estimated  upstream discharge with other known flow parameters upstream of the dam form the basis for designing the intake tower. Model will be design to give the parameters of any intake tower given the height. The seismic action using the concept of response spectrum which provides the maximum value of ground acceleration as a function of the structure vibration period is not consider.

1.5 Justification of the Study

Today’s competitive world has forced engineers to realize more economical designs and designers to develop more effective optimization techniques. This thesis work is on optimum the design of water intake tower for an Earth Dam and using RFEM structure analysis as the optimization tool. Columns are primary elements in any structure and are thus very important for the stability of any structure  as  they play a vital  role in  resisting both  vertical  and horizontal loads. Due to inaccuracies in loading and construction, non-homogeneity of materials,  imperfect  placement  between  beams  and  column,  and  in  situations  where  the column is a corner one, there is always some eccentricity in the member thereby subjecting it to biaxial bending.

Genetic algorithm (GA) method determines global optimum solutions as opposed to the local solutions determined by a continuous variable optimization algorithm (Arora, 2012). The characteristics of GAs such as the ability of handling both continuous and discrete variables, not  needing  gradient  information,  and  their  applicability  to  a  population  of  candidate solutions, make GAs popular and efficient optimization techniques (Arora, 2012).

The continuous search for optimality, the promising technique of genetic algorithm in achieving optimum solutions to structural design problems, lack of adequate research specifically in the area of optimization of reinforced concrete column as well as the challenge of becoming one of the researchers in such a tasking field motivated the thesis work.

₦8,000.00 – DOWNLOAD FULL PROJECT DOWNLOAD FULL PROJECT Added to cart

---

---

---

---

Related Project Topics :