Investigating the degradation factors of the end walls of the relaxation basin of concrete dams and its remedial solutions, a case study of Doz regulatory dam.

Thesis of M.Sc.  

Discipline: Civil Engineering

Trend: Hydraulic Structures

Abstract

Restriction of rivers with any motive is generally done by dams and similar structures. The flow passing through these structures has a significant potential for erosion and scouring of susceptible beds. Relaxation ponds are designed and built mainly for the purpose of depleting flow energy and maintaining the security of hydraulic structures against possible forces. The intensity and pattern of flow inside these structures can seriously expand downstream erosion. The current research is the result of a numerical study and three-dimensional simulation on the process of scouring the bed in the downstream of the relaxation pond of Doz regulatory dam; Therefore, at first, using dimensional analysis, dimensionless parameters affecting scouring were identified; Then, experiments were conducted under different times on the solid profile of the Doz regulatory dam flume, with maximum flow conditions (design flow), non-uniform bed materials (combination of fine and coarse sand and gravel) and using the FLOW-3D model; After that, the effects of each of the effective parameters, such as flow parameters, characteristics of bed particles, threshold speed of particle movement, rigid profile geometry of relaxation basin and the role of time development on scour continuity and bed changes profile were extracted. The most important results obtained show; that the appearance of the most erosion occurs when the asymmetric flow patterns dominate the model and the bed materials are not determined in accordance with the conditions of stability and the threshold velocity of particle movement.

Key words: erosion, solid profile, movement threshold velocity, non-uniform bed, DOZ regulatory barrier

Chapter One

Introduction

Erosion [1] in science Fluid mechanics is the change of shape and displacement that a fluid creates due to its movement on the surfaces that it moves near. As an example, the movement of air fluid in the form of wind in the desert, which leads to the erosion of loose sands and causes them to change shape and move somewhere. Especially in hydraulic science, where the fluid in question is water, erosion is of special importance and it is called the phenomenon of waterlogging [2]. This importance originates from the fact that human life has been formed along the rivers and coasts throughout history, and this means the constant confrontation of man with the effects of this phenomenon. Coasts and rivers or built in their vicinity are always subject to damage and destruction. This has motivated to know the laws governing the science of fluids and to know hydraulic flow. In particular, this view has become more scientific in the last 100 years and has prompted researchers to find suitable solutions to reduce this phenomenon by knowing the effective parameters and the impact of each of them (Parsmehr, 2019).

One of the most important factors in the destruction of hydraulic structures is scouring around them. Therefore, in order to prevent and reduce its effects, it is necessary to know its mechanism. River bed materials are susceptible to erosion, but the intensity of this erosion depends on time. So that the bed of rivers covered with granite takes many years to erode, while rivers with sand bed have the maximum scouring depth in a very short period of time. In addition to the structure of the land and rivers, which is one of the important factors in erosion, hydraulic factors also play a significant role in the occurrence of this phenomenon. Relaxation ponds are designed and implemented as required structural members downstream of dams and in the direction of depleting destructive kinetic forces. This structure, especially in flood conditions, can play an effective role in controlling and restraining flood flows after leaving the dam and before entering the river. Therefore, the precise design and implementation of these structures, especially in the upstream of the irrigation and drainage networks, can improve the operation management and maintenance of these vital hydraulic irrigation arteries. This matter is very important downstream of the Dez regulatory dam and upstream of the Dez diversion dam, because controlling and restraining destructive currents in regulating the restrained flows of the transmission and distribution channels and timely water supply to the downstream farms is important for all the operators and managers of these networks. Due to the importance of the balance and stability of these structures, any scouring can disrupt the efficiency of the use of the structures.Therefore, the study and investigation of various dimensions of scouring process is considered in this study so that the challenges in the emergence and creation of this hydraulic problem can be controlled and managed. 1381 In this area, the relaxation ponds below the hand of destruction and under the side walls also have scours.

Despite the importance of paying attention and studying the failures in the phases after the construction of water structures, most of the existing engineering literature is focused on how to design, and a major gap between construction and exploitation problems is evident, and despite the importance of optimal exploitation management, there are still few articles and research results for expert exploitation. The lower reaches of the relaxation basins of the Dez regulatory dam have moved upwards over time, causing fractures in the relaxation basin and eventually, together with the scouring of the sides, they will become a threat to the stability of the dam, so it is necessary to revise the discharges of the design of the basin structure or the way the valves are used, therefore, from a theoretical point of view, the need for a research that can be a suitable analytical framework for the use of experts and engineers is felt. The aim of this is to provide a comprehensive and comprehensive analysis with theoretical support in order to promote expert methods in strengthening the hardware management of these structures, which leads to results such as optimal efficiency of existing facilities and departure from the existing situation with the aim of moving to a favorable situation.

1-1 Statement of the problem

Relaxation ponds are designed and implemented as structural members required downstream of dams and in the direction of depleting destructive kinetic forces. This structure, especially in flood conditions, can play an effective role in controlling and restraining flood flows after leaving the dam and before entering the river. Therefore, the precise design and implementation of these structures, especially in the upstream of the irrigation and drainage networks, can improve the operation management and maintenance of these vital hydraulic irrigation arteries. This matter is very important in the downstream of the Dez regulatory dam and upstream of the Dez diversion dam, because the control and containment of destructive currents in the regulation of the restrained flows of the transmission and distribution channels and timely water supply to the downstream farms is important for all operators and managers of these networks. Considering the importance of the balance and stability of these structures, any scouring can disrupt the efficiency of the use of the structures. Therefore, the study and investigation of various dimensions of scouring process is considered in this study so that the challenges in the process of emergence and creation of this hydraulic problem can be controlled and managed.

Doz regulatory dam in the geographical basin of Khuzestan province, Dezful city has two relaxation ponds of different dimensions and designs in order to consume energy, one of the ponds is designed to relax the water released from the irrigation valves and the other is specially designed for the discharge valve. The sediments have been designed that due to the winter flood of 2011 in this area, the calm ponds have been destroyed and there have been scours under the side walls.

Many researches have been carried out in the field of local scouring of the bed due to the passing current and significant results have also been obtained. Since the scouring issue is complex due to the multitude of factors that affect it, most of the studies have been conducted in a laboratory manner. Therefore, in this research, it is tried to evaluate the results of the numerical simulation by the three-dimensional flow software model Flow-3D, with field investigations and manual calculations, in order to fully understand the causes of the problem, to test the power of the numerical model in this field and to use this type of model instead of the laboratory model in similar conditions.

Flow-3D software solves the equations governing the fluid using finite volume approximations. Also, the flow environment is divided into a grid with fixed rectangular cells, where there are average values ??of dependent quantities for each cell.