الفهرس 
Literature ReviewOnly 14 pages are availabe for public view
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Abstract
A diaphragm is a thin impervious wall that is used in the core area of the dam to prevent the seepage of water. Any fault in the diaphragm can reduce its efficiency and threaten the safety and stability of the dam. Extensive evaluation of the influence of diaphragm fracturing on dam safety is required to establish a safe design and offer the appropriate measures. This study investigates the effect of diaphragm cracking on the safety of the dam for seepage and slope stability. First, a permeability tank experimental model is used to validate the numerical model. After that, different scenarios for cracked internal diaphragms are studied numerically. The crack’s height, thickness, inclination direction, and number are all investigated. The effect of having a downstream horizontal drain with cracked internal diaphragms is also evaluated. The results showed that internal diaphragms are very beneficial for the safety of earth dams. They can reduce seepage discharge by more than 98%, significantly minimize the velocity downstream, lower the pore water pressure, and increase the critical factor of safety of the downstream slope by 34%. The most critical location of a crack in an internal diaphragm is near the base of the dam, wider cracks are more destructive, and the most critical direction is the horizontal crack. The fracturing of the diaphragm at multiple locations is detrimental to the safety of the dam as it causes the diaphragm’s efficiency to DROP and approach the case of its nonexistence. Moreover, the study found that a properly designed horizontal drain can be used as a mitigation measure to safeguard the dam against failure if diaphragm fracturing occurs.
In addition, the study evaluates the efficiency of grouted concrete diaphragms, which are commonly used to rehabilitate old dams that started to leak. Such grouted diaphragms can be subject to construction defects which cause further seepage issues and threaten the dam’s safety. Thus, this study also implements the permeability tank and numerical models to simulate the effect of using a grouted diaphragm on the seepage and stability of existing earth dams. The negative effects of some construction (execution) defects are also highlighted. Thickness deficiency, cracking, and concrete mixing and pouring defects are considered. Different scenarios for the grouted diaphragm without and with construction defects are modeled. Additionally, the effect of using a toe drain to reverse the negative impacts of such defects is studied. The seepage discharge, velocity, hydraulic gradient, pore water pressure, and downstream slope stability are evaluated. The results showed that using the grouted diaphragm reduces the seepage discharge and increases the stability of the downstream slope. Partial grouting increases the velocity at the diaphragm’s free end. The penetration depth is the most effective parameter for the diaphragm’s efficiency. The most detrimental defects of a grouted diaphragm are the cracks at its lower end and its high hydraulic conductivity. Using a toe drain slightly increased the seepage discharge, but greatly lowered the pore water pressure and enhanced the downstream slope stability. Hence, it is recommended to add a concrete grouted diaphragm that penetrates the full height of the dam along with a toe drain to rehabilitate earth dams.