Study on formation and expansion condition of hidden soil cavity under condition of groundwater exploitation in karst areas

This paper uses an analytical method to analyze soil cavity forming conditions and the associated mechanics. On this basis, the paper studies the soil cavity expansion rule and reveals the nature of the soil cave collapse from the mechanism angle. The results show the following: (1) the spalling force caused by pumping at different points around a soil cavity varies. The nearer the point to the pumping well, the easier it is for the soil cavity to expand. (2) The nearer the point to the soil cavity roof, the greater the spalling force, indicating that the roof is easier to expand outward than a wall. (3) The expansion condition of a soil cavity is that the spalling force is greater than the cohesive force of the soil mass. With the expansion of the soil cavity, the spalling force increases. When the soil cavity begins to expand outward, the soil cavity shows trends of development due to the increasingly larger spalling force. (4) The spalling force influencing the expansion of the soil cavity is proportional to the pump drawdown and hydraulic gradient. Thus, the water level drawdown and flow must be controlled while pumping to control generation of soil cavities. The research results of soil cavity forming processes can be used as a theoretical reference for controlling karst collapse in the region.