| Karst ground collapse belongs to the geological disaster of ground collapse type.Due to the universality,harmfulness,recurrence,concealment and sudden occurrence of ground collapse,more and more attention and research have been paid to it.However,a unified and systematic theoretical system has not been formed yet.Therefore,researches on the inducing factors,collapse mechanism and disaster prevention and control of ground collapse have been carried out.This thesis is mainly divided into three processes,model design,laboratory test and theoretical analysis,to study the collapse evolution law of karst stratum induced by the drop of karst water level under the condition of underground water level at different incline angles:Evolution process of karst ground collapse is the bedrock,the interaction between soil and water,is the problem of stress field and seepage field coupling,based on the existing production mold situation investigation of rock mass,we design a control structure surface preparation parameters,such as opening,shape and occurrence of types of rock specimen mold,can be used to study the interaction between water and rock mass.In order to explore the interaction between soil and water flow,a set of physical model device including model box,sand bag and suspension device is designed,which can control the inclination angle of underground water level and the height of karst water level.On the basis of determining the model test scheme and flow,a monitoring system is set up for the subsidence of the central line of the surface,the total amount of seepage in karst channels,the soil and water pressure in the soil,the grading of sand leakage and the spatial form of the collapsed body,so as to obtain the time-varying curves of the collapse causing factors or response parameters in the collapse process of the karst ground.Based on the level of underground water level experimental center of pore water pressure,surface subsidence,karst channel seepage quantity and the vertical earth pressure test data,from the karst surface collapse,before and after the two stages of karst ground collapse in three levels and the internal collapse phase,refining the stages of evolution characteristics,the outline of the underground water level of karst ground collapse in evolution.Furthermore,the evolution process of karst ground collapse of test groups with different inclination angles is compared.The theoretical model of seepage flow in karst passage is established,the calculation formula of seepage flow in karst passage is derived in the initial state,and the calculation method is put forward to analyze the change of groundwater level height and permeability coefficient after the karst water level drops,and the rationality of the method is qualitatively verified by the test data analysis.Based on the theory of loose earth pressure,the formulas for calculating vertical stress in loose area under three different states of anhydrous,hydrostatic and stable seepage are derived.On this basis,the loose earth pressure in roof of soil cavern under different states of underground water level test group is calculated and analyzed without considering viscosity.Under the condition of considering viscosity,the loose earth pressure of roof of soil cavern in test groups with different inclination angles was calculated and analyzed. |
