Dam filter design and seepage safety evaluation of asphalt concrete corewall gravel dam of Zhirui Pumped Storage Power Station

According to the operating conditions of frequent water level changes and large water level fluctuations during the operation period of pumped storage power stations, aiming at the shortcomings of poor anti-permeability and erosion capability of natural gravel materials, the first asphalt concrete core wall dam of a pumped storage power station under construction in China, which uses gravel materials to build dams and fills directly on the riverbed cover, is taken as an examples. Based on the shortcomings of the current filter criterion that only pays attention to the gradation relationship and ignores the influences of the relative density on the permeability of gravel materials, a modified filter criterion of gravel materials is proposed, and it is verified through the filter design of the core wall gravel dam body, the seepage test of dam materials in each area and the seepage safety analysis of the dam body. The results show that in addition to the gradation characteristics, the change of the relative density in the filter design is also crucial to the filter protection capability. Due to the poor permeability of natural sand and gravel materials, in the process of rapid decline of reservoir water level, the pore water in the sand and gravel dam cannot be discharged in a short period of time. The falling speed of the infiltration surface in the dam is far lower than that of the reservoir water level, and there is a significant lag phenomenon. With the change of water level, there is a phenomenon that the seepage gradient in the dam is greater than the allowable gradient. The filter protection design of each sub-interval of the dam is carried out by modifying the filter criterion. It can effectively deal with the seepage stability problem of gravel materials at the waterward side of the core dam caused by the frequent change of reservoir water level and the large fluctuation of water level during the operation of pumped storage power stations. Based on their excellent mechanical properties, abundant reserves and convenience for construction, the local gravel materials are also the good natural ones for constructing the dams of pumped storage power stations.