Experimental and Theoretical Study on the Stratum Cavity Collapse Induced by Water and Sand Leakage in Subway Tunnels

Stratum cavity collapse induced by water and sand leakage in a subway tunnel is a sudden urban geological disaster, which can cause serious casualties and economic losses. In response to the hazards of stratum cavity collapse induced by water and sand leakage around subway tunnels, a set of visual test devices with variable hole diameters were designed to simulate the stratum cavity collapse induced by water and sand leakage under comprehensive consideration of the size of the cavity diameter, clay thickness, clay strength, and so on. Based on pressure arch theory and unified strength theory, a critical calculation formula was established for stratum cavity collapse under two modes, of tensile shear and shear failure. Furthermore, the accuracy of the theoretical calculation formula was verified by experiment. The results show that the critical radius increases with the increase of clay strength and decreases with the increase of buried depth and friction angle. Clay soil is more prone to shear failure at the arch foot under the same conditions. The larger the soil sand mix ratio and the cavity diameter, the smaller the critical water pressure of soil collapse. The thicker the soil layer, the greater the critical water pressure. The theoretical analysis method has a clear physical meaning and the theoretical results agree well with the test results. The research results are of great significance for the warning of and prevention of such urban geological disasters.