Experimental study on permeability characteristics of red sandstone under cyclic seepage pressures

The cyclic fluctuations of reservoir water level make the soft rock in bank slope below the flood control level (FCL) under cyclic seepage pressures and will bring great effects on its permeability characteristics. In order to obtain the variable characteristics of the soft rock under cyclic seepage pressures, permeability tests on red sandstone specimens from Three Gorges Reservoir area, China under cyclic seepage pressures are conducted to simulate cyclic fluctuation of reservoir water level by using the self-developed equipment. The test results show that the cumulative volume of water infiltration has a fastest growth under the first periodic seepage pressures and then decreases under the following cyclic seepage pressures, while the penetration rate and permeability coefficient of the sandstone specimens periodically change with the cyclic variation of seepage pressures. There are some differences in the change of the cumulative volume of water infiltration, penetration rate and permeability coefficient for different specimens. But after four infiltration cycles, the cumulative volume of water infiltration, penetration rate and permeability coefficient of red sandstone vary in the same trend and within a stable range. The study indicates that the permeability characteristics of the red sandstone in bank slope below FCL in Three Gorges Reservoir Area gradually begin to be stabilized after a few number of cyclic fluctuations of reservoir water level.