Analysis of damage mechanism and mechanical conditions of karst soil caves at different evolution stages under strong water level fluctuation

Abstract

Abstract The study of the evolutionary characteristics of the trajectory of karst soil caves from development to collapse is an important basis for the analysis of damage mechanism and the study of critical mechanical conditions. Combining the field collapse phenomenon and indoor research, the author summarized the characteristics of different evolutionary trajectory stages and generalized the evolutionary stages of karst earth caves. On the basis of the research on the damage mechanism and mechanical theory conditions of different evolutionary stages of the lineage, it is concluded: (1) In the early gestation stage of karst soil cavities, soil particles in the fine pores are subjected to two kinds of forces: normal stress and shear stress. The normal 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. Whereas the water level fluctuation of groundwater is closely related to the superstatic pore water pressure, the flow rate of groundwater is related to the dynamic water pressure, and the soil particles begin to spall off beyond the critical water level amplitude, and the soil particles disintegrate and migrate beyond the critical flow rate; (2) Karst soil hole arch progressive stage, the inner wall of the small hole before soil hole expansion has isotropic effective stress, with the increase of internal pressure, the spherical region will be from the elastic state into the plastic state, if the normal effective stress is greater than zero, the soil hole wall will be tensile damage, resulting in the further spalling and expansion of the soil hole; (3) The overall destruction stage of the karst soil hole, the existence of the critical height of the arch soil hole at the time of the arch collapse. In the cylindrical collapse pit formation, there exists the critical friction force of the side wall of the cylindrical unit body. At the time of funnel-shaped collapse pit formation, there exists cylindrical collapse pit sidewall critical depth.