STUDY ON RESPONSE OF COVERED KARST SOIL CAVE TO GROUNDWATER CHANGES AND ITS COLLAPSE EVOLUTION PROCESS

Karst collapses are developed in Fujian Province and are second only to landslides and collapses. In order to study the evolution process of karst collapse, the typical covered karst collapse in Fujian Province is taken as the research object in this paper. On-site soil samples were taken. Fiber-optic grating strain sensors, pore water pressure gauges, settlement gauges, and other monitoring instruments were installed in a self-made physical model box to obtain stress and strain information of the overburden soil under different conditions. The response of the overburden soil is analysed. The development and evolution process of typical overburden karst collapse is proposed. The results show that: (1)Under the effect of the pore water fluctuations in the Quaternary overburden, the pore water pressure of the soil layer changes basically at the same amplitude. The largest deformation occurs in the top soil while the smallest deformation occurs in the subsoil. The fluctuation of the water level has little damage to the soil, and the soil cave has not formed yet. (2)In the process of the karst water level rising and falling repeatedly, the pore water pressure increases and decreases synchronously with the change of the seepage water level. The soil closer to the cave on the same horizontal plane produces greater strain. The higher the soil layer, the greater the strain difference. The deformation of the roof of the soil cave continues to develop upwards under the action of hydrodynamic force and vacuum erosion. When the deformation develops beyond the critical soil cave height of 40cm, the ground collapse occurs. (3)The evolution process of typical covered karst collapse can be divided into three stages: the first stage is the development and formation of soil caves, the second stage is the internal collapse, and the third stage is ground collapse. (4)The karst soil cave collapse in southwestern Fujian mostly occurs in the strong groundwater runoff drainage area on both sides of the intermountain basin and the valley. The overburden layer is thick, mostly composed of the Quaternary alluvial gravel, gravel-bearing clayey soil, and silty clay layer. The disaster mechanism has its regional characteristics.