Analysis of Subsidence Induced by Negative Pressure from Precipitation in Covered Karst Soil Cave and Its Morphological Effects
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摘要:
为揭示覆盖型岩溶降水引发的土洞洞内气压变化规律及其致陷机理，基于气体短管淹没出流理论，提出椭球形土洞内气体渗流流量、气压及稳定性系数的计算方法，并基于有限差分数值解编制相应的MATLAB程序；通过岩溶土洞降水致陷的室内模型试验验证计算方法的可行性. 算例分析结果表明：土洞气体状态参量（流量与气压）及其稳定性系数在降水过程中经历了从初始状态到降水前期剧变、过降水后期缓变的过程，最终逐渐恢复至起初状态；降水土洞的最大峰值流量与椭球土洞短半轴长$ b $正相关，与长、短半轴长之比（$ a / b $）及拱高负相关；最小峰值气压均与$ a / b $、$ b $及拱高正相关；最小峰值气压抵达时间与拱高正相关，与$ a / b $负相关，$ b $影响甚小；降水土洞最小峰值稳定性系数与$ a / b $及拱高正相关，与$ b $负相关；最小峰值稳定性系数抵达时间与拱高正相关，与$ a / b $则负相关，$ b $影响甚微.
Abstract: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. -
图 1 土洞降水致陷力学模型
Figure 1. Mechanical model of subsidence induced by precipitation in soil cave
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