Study On The Influence Of Groundwater Level Fluctuation On The Collapse Of Karst Soil Caves And Its Collapse Mechanism

This study takes the karst collapse prone area in Lingui District,Guilin City as the geological background,and aims to simulate the process of karst soil cave collapse induced by the fluctuation of water level under different initial water levels and drainage rates through a combination of model tests and numerical simulations for a one-dimensional red clay cover layer.The relationship between water level fluctuations and cover layer deformation is established,The collapse mechanism of karst soil cave collapse caused by the fluctuation of groundwater level has been proposed.(1)The fluctuation of groundwater level in the research area is the main hydrodynamic factor accelerating the collapse of karst soil caves.The initial water level height and drainage rate do not change the law of water level fluctuation induced karst soil cave collapse,but only affect the amplitude of key collapse causing factors,thus having varying degrees of impact on the evolution process of karst soil caves.(2)It was clarified that the soil pressure and deformation of the overburden layer in the study area depend on the changes in water-gas pressure inside the existing soil cave caused by the fluctuation of water level.The dynamic response of overburden deformation is positively correlated with drainage rate and initial water level height.The drainage rate is fast,the initial water level is high,the deformation and response of the overlying layer are faster,and the water level fluctuation period is small,the fluctuation frequency is less,accelerating the evolution process of karst soil caves.(3)The initial water level height is positively correlated with the degree of softening of the overlying soil.The higher the initial water level,the stronger the soaking softening effect on the overlying soil,and the more likely the soil cave is to collapse.The drainage rate is positively correlated with the magnitude of water level drop.The faster the drainage rate,the greater the depth of water level drop,and the stronger the negative pressure suction effect on the overlying soil of the soil cave,making the soil cave prone to collapse.The process of water level decline is more prone to collapse in soil caves compared to water level rise.(4)A karst soil cave model was established to display the distribution of displacement,stress,and plastic zone of the karst soil cave and the overlying soil under two hydrodynamic conditions,and based on the conclusions of model experiments,the action law of water level fluctuations on karst soil caves is proposed.(5)The development and evolution stages of karst soil caves induced by fluctuation of water level are divided.It can be roughly divided into three stages,namely soil softening stage,slow collapse stage and rapid-overall collapse stage.(6)It is clarified that the formation of karst soil cave collapse induced by water level fluctuation is the result of the combination of seepage erosion,vacuum negative pressure suction and positive pressure gas explosion,and the three collapse mechanisms have different relative effects on the evolution of soil cave.