Research on identification of critical factors and critical warning conditions under the perspective of safe groundwater exploitation ----- A Case Study on Safe Mining of Karst Water in Jiangsu Province, China

Abstract Compared with traditional groundwater, underground karst water has the attributes of high degree of enrichment, stable dynamics, ease of exploitation and good water quality. However, in recent years, with the rapid development of China's cities, the rapid growth of karst water mining has led to a series of karst collapse and other geological disasters. How to weigh the karst water resources both to exploit, but also to ensure geological safety, this invisible "double-edged sword" is placed in front of many researchers in the problem. By sorting out the intrinsic and extrinsic influencing factors during the development of karst soil caves in karst areas, and through the physical modeling test of karst soil cave evolution, the author has studied the influence of different factors on the amount of soil particles lost and the amount of displacement and deformation during the development of karst soil caves. And based on the sensitivity analysis method, it is concluded that the most sensitive ones are groundwater activity and air pressure difference effect. Then the mechanical theory and damage mechanism of the sensitivity factors on the development process of karst soil caves were studied, and the critical warning model of karst soil cave damage was established, and the critical warning conditions based on the sensitivity factors were analyzed and derived:(1) In the early gestation stage of karst soil cavities, soil particles in fine pores are subjected to positive and shear stresses. The positive stress is caused by the super-static pore water pressure, and the shear stress (drag force) is caused by the dynamic water pressure acting on the side of soil particles;(2) The water level fluctuation of groundwater is closely related to the superstatic pore water pressure, and the flow rate of groundwater is related to the dynamic water pressure, which exceeds the critical water level amplitude soil particles begin to spall, and exceeds the critical flow rate soil particles disintegrate and migrate;(3) The critical amplitude of water level fluctuation required for soil particle spalling was derived by studying the relationship between head loss during pore seepage at the early gestation stage of karst earth cavities and superporous water pressure and dynamic water pressure;(4) Based on the relationship between critical shear stress and critical flow rate, the expression for the critical flow rate required for soil particle migration was derived. The critical pumping volume can be converted to the critical pumping volume based on the relationship between the critical water level fluctuation amplitude and the critical flow rate in engineering applications, and then the pumping volume can be controlled to eliminate the formation of early soil hole prototypes.