Analysis of Subsidence Induced by Negative Pressure from Precipitation in Covered Karst Soil Cave and Its Morphological Effects

In order to reveal the air pressure variation law and the subsidence mechanism in covered karst soil cave induced by precipitation, according to the theory of short gas pipe submerged flow, calculation methods of gas seepage flow, air pressure, and stability coefficient in ellipsoid cave were obtained. MATLAB program was compiled based on finite difference numerical solutions. The feasibility of calculation methods was verified through indoor model tests of subsidence induced by precipitation in a karst soil cave. The example analysis has shown that the gas state parameters (flow and pressure) and stability coefficient of the cave evolved from the initial state to drastic variations in the early stage of precipitation, then shifted to gradual changes in the later stage, and finally returned to the initial state. The maximum peak flow of soil cave induced by precipitation is positively correlated with the length of the semi-minor axis b of the ellipsoid cave, and negatively correlated with the ratio of semi-major axis and semi-minor axis $ a / b $, and arch height. The minimum peak air pressure is positively correlated with $ a / b $, $ b $, and arch height. The arrival time of the minimum peak air pressure is positively correlated with arch height, and negatively correlated with $ a / b $, while the effect of $ b $ is negligible. The minimum peak stability coefficient of soil cave induced by precipitation is positively correlated with $ a / b $ and arch height and negatively correlated with $ b $. The arrival time of the minimum peak stability coefficient is positively correlated with arch height, and negatively correlated with $ a / b $, while the effect of $ b $is negligible.