Study On The Collapse Mechanism Of Karst Soil Cave Under The Action Of Precipitation Funnel

In recent years,the surface collapse in covered karst area caused by precipitation funnel formed by underground engineering activities such as mining and subway construction has become a common natural disaster that seriously threatens the safety of people's lives and property.At present,there are few reports on the mechanism of surface collapse in covered karst area under the action of precipitation funnel.By collecting a lot of engineering data,this paper generalized the geological model of karst collapse under the action of precipitation funnel in covered karst area,the collapse mechanism of karst soil cave under the effect of precipitation funnel by means of theoretical analysis,physical model test and numerical simulation was studied,and the following main results was obtained:(1)On the basis of previous research results,it is concluded that upper overburden with certain thickness,karst cave with upward opening and hydrodynamic action are the three basic conditions for karst collapse,and the collapse mechanisms of suffosion,vacuum suction erosion and osmotic pressure action were analyzed in detail.The typical geological structure model of karst soil cave collapse area under the action of precipitation funnel was generalized.The upper part is overburden layer with unitary or multiple structure,and the lower part is bedrock with uniform cracks.It provides the theoretical basis for the study of the soil cave collapse in karst area under the action of precipitation funnel(2)Based on the generalized geological structure model of covered karst collapse area under the action of precipitation funnel,a test device was developed to simulate the covered karst collapse under the action of precipitation funnel.The device also can simulate the covered karst collapse caused by many factors such as mine drainage or water inrush,groundwater level fluctuation,etc.(3)The stability of overburden layer with different clay content and different soil hole size was tested in static water.The results show that the smaller the diameter of soil hole,the better the stability in static water.There is a critical value for the influence of clay content on the stability of soil hole,and the stability of soil hole is best at the critical value.(4)The results show that the curves of precipitation funnel have similar change characteristics under different drawdowns.It falls steeply near the high water level,shows a gentle variation trend between the high water level and the low water level,and plunges again near the low water level.And the greater the drawdown,the more obvious the trend is.(5)The size of soil hole is the main factor affecting the soil layer collapse under the action of precipitation funnel.The larger the diameter of soil hole,the greater the scouring effect.The smaller the maximum displacement of the soil arch shoulder near the high-water level,the more likely the soil hole is to be damaged.The permeability coefficient has less influence on the collapse of soil hole,mainly through affecting the characteristics of the flow field of the precipitation funnel.The larger the permeability coefficient,the denser the streamline distribution around the soil hole,and the stronger the scouring effect on the soil hole.(6)The collapse of soil hole was caused by the shear deformation of the soil arch shoulder near the high water level around the soil tunnel under the scouring of water flow,and then the plastic yield zone through the soil arch body was formed,which leads to the instability of the soil arch and the collapse.Figure 51 Tablell Reference 72...