The Study On The Model Test And Prediction Method For Shallow Surface Karst Collapse Induced By Tunnel Water Inrush

In recent years,with the construction of the large tunnel engineering in karst mountain areas,the karst water inrush disasters are increasing.The karst water inrush disasters are often accompanied by the rapid decline of the groundwater level,and further induces the shallow surface karst collapse.The formation of karst collapse is affected by topography,landform,lithology,geological structure,hydrogeological conditions,meteorology,time,space and other factors and this determines the complexity of the forming mechanism of karst collapse and the complexity and arduous of the prevention and control of karst collapse.At the same time,because of the restriction of the field conditions,it is difficult to carry out the study of the mechanism of karst collapse and the changing of the mechanical characteristics of the overlying soil during the karst collapse directly through the field test.On the basis of the summary and analysis of the present research status of karst collapse at home and abroad,through the research and analysis of the formation conditions of karst collapse,the influence factors of the collapse,the expansion mechanics of the soil cave and the geological generalization model of the typical collapse,the cohesive soil is selected as the karst cover layer and the model test simulating karst collapes inducde by water inrush disaster of tunnel in karst mountain area is carried out based on the indoor sand box test.The law of the deformation and collapse of the overlying soil layer is simulated with the thickness of the cover layer,the opening size of the cave and the water supply condition,and the method of the prediction of the karst collapse is studied according to the monitoring results.The following results are obtained.(1)Through the analysis of the basic conditions of soil cave formation,mechanical analysis of soil cave expansion and the mechanism of surface collapse,the collapse mechanism of karst collapse under different conditions is summarized.(2)Based on the theoretical analysis of the mechanism of karst collapse,a physical test model is designed to carry out the model test on the internal development of karst cave under the different collapse effects(potential erosion,disintegration,vacuum suction and seepage pressure).The law of soil cave development under different collapse effects is analyzed,and the corresponding mechanism of karst collapse is revealed.Combined with GPR,the mechanism of development and expansion of soil cavities and the changes of internal structure of soil layers under water inrush are studied.(3)According to the influence factors of soil cave development,9 groups of orthogonal model tests are designed to study the dynamic changes of strain and stress in different positions of soil layer under the conditions of different hole size,cover thickness and water inrush amount.The variance analysis of orthogonal experiment was carried out based on the abrupt change of soil pressure,and the sensitivity of various factors was analyzed.(4)Based on the monitoring data of model test,a prediction method for karst collapse based on IOWHA operator combination model is established.