Abstract: In order to explore the seepage stability of slurry cake formed in the cutoff wall hole of coarse-grained soil, the impermeable characteristics of slurry cake are tested by the self-made slurry seepage apparatus. After the slurry cake wall is formed by the slurry seepage through sand samples with some particles gradation under some pressure difference, the seepage experiments of water passing through the frontal face of slurry cake or through the reversal face of slurry cake are carried out under some pressure difference. Through the analysis of test results, the following knowledge are obtained. The cutoff effect of slurry cake bearing with large gradient is significant. There are different seepage characteristics of slurry cakes formed under different pressure differences. The greater the pressure difference when the slurry cake are formed, the more compact the slurry cake is, the stronger the ability is to resist infiltration and damage, the smaller the permeability of the slurry cake is. The impermeability of water passing through reversal face of slurry cake under some pressure difference is smaller than through frontal face of slurry cake under same pressure difference. With the sustaining time of hydraulic action increasing, the structure of slurry cake will change and its seepage velocity also increases. Under the large hydraulic gradient action the slurry cake damage may occur under certain osmotic pressure difference. The critical hydraulic gradient is closely associated with the loading pressure difference of slurry cake formation. The larger the pressure difference is, the larger the critical hydraulic gradient is. On the contrary, the smaller the critical hydraulic gradient is. The above-mentioned knowledge has theoretical and practical importance that the design method and construction technology of cutoff wall in large depth covering layer is improved by investigating the impermeable characteristics of slurry cake.

Key words: large depth overburden layer, slurry seepage experiment, slurry cake, the impermeable characteristics