عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Worldwide, over 45,000 large dams have been built, and nearly half the world's rivers are obstructed by a large dam. The belief that large dams, by increasing irrigation and hydroelectricity production, can cause development and reduce poverty has led developing countries and international agencies such as the World Bank to undertake major investments in dam construction. By the year 2000, dams generated 19 percent of the world's electricity supply and irrigated over 30 percent of the 271 million hectares irrigated worldwide. However, these dams also displaced over 40 million people, altered cropping patterns, and significantly increased waterlogging of arable land. Dams are artificial barrier usually constructed across a stream channel to store water in a reservoir which is then used for a variety of applications such as irrigation and municipal water supplies. Dams must have spillway systems to convey normal stream and flood flows over, around, or through the dam. Spillways are commonly constructed of non-erosive materials such as concrete. Dams should also have a drain or other water withdrawal facility to control the water level and to lower or drain the lake for normal maintenance and emergency purposes. Dams are constructed especially for water supply, flood control, irrigation, energy production, recreation, and fishing. Dams are mainly divided into four parts on the basis of the type and materials of construction as gravity dams, buttress dams, arch dams, and embankment dams. These dams are divided into two types: homogeneous and non-homogeneous earth dams. Non- homogeneous dams are made of different parts that each part has much influence separately on the dam body’s performance, stability, and other design components. In designing of an earth or the rock fill dam, the foundation, abutments, and embankment should be considered as a unit. The entire assemblage must retain the reservoir safely without excessive leakage. Provisions for seepage control have two independent functions. The first is the reduction of water losses to an amount compatible with the project purpose. Another independent function is that, eliminating the possibility of structural failure by piping. It may also be concerned with the stability of construction slopes and slopes around the reservoir after impoundment. One of the most important components in dam designing is the dam core. The dam core is a significant factor in caulking and controlling dam body seepage.
One of the key aims of this study is to develop the numerical model for measuring seepage through a dam, stability factor and hydraulic gradient based on materials and geometry specification of earth dams. The methodology includes parts such as: Simulated annealing algorithm, modeling and optimization part that included seepage model, slope stability model and hydraulic gradient model.
In this study, a new model is proposed to predict the seepage rate, slope stability, hydraulic gradient in a non-homogeneous earth dams using Geo-Studio software. Thorough this model, seepage, slope stability, and hydraulic gradient are formulated by different factors which are related to material properties and geometric dimensions of the dam. It should be noted that permeability in shell for the non-homogeneous earth dams are more than core. Hence, the seepage rate for the shell can be ignored because existing remarkable difference between shell and core dam. Therefore, the core can be considered as a homogeneous dam. In this research, 150 assumed sections with different materials and dimensions are designed.
In this paper, new regression models including leaking from the dam body model, hydraulic gradient model, and stability safety factor model were developed to calculate the designing variables. The results indicated the high performance of new regression models for determining the coefficient of stability, leakage from the body, and hydraulic gradient. For developing the necessary model, hydraulic gradient and stability safety factor were considered as constraints. Also, the multi objective function was expressed as reduction of seepage through the dam body, and the volume of core material is minimized. This problem was optimized using the Shuffled complex evolution (SCE). The SCE method combines the strengths of the simplex procedure with the concept of controlled random search, competitive evolution and the newly developed concept of complex shuffling. As the search progresses, the entire population tends to converge toward the neighborhood of the global optimum. The results of modeling were compared by the actual geometry of Birjand Hesar Sangi earth dam. A result indicates the 24 percent reduction of material type in dam core and 8.5 percent reduction in dam shells. The high performances of the integrated developed model demonstrate the capability of this model in optimal design of earth dam on stable condition.