The Three-Dimensional Collapse Mode Of Surrounding Rock Of Deep Buried Cavity Induced By A Concealed Karst Cave

Convenient,fast and efficient transportation is a reliable guarantee for the stable growth of Chinese national economy.Therefore,on the premise that the construction of transportation infrastructure has made great achievements,China is still strengthening the construction of transportation infrastructure,especially in the areas with relatively backward transportation facilities,such as the central and western provinces.Most of these areas are mountainous,with complex terrain and extensive karst landform.It is greatly common to see karst caves around the newly-built tunnel or even on the axis.However,karst caves are easy to induce the collapse of surrounding rock in the process of tunnel construction,which poses a great threat to the construction safety of the tunnel.Aiming at this phenomenon,based on Hoek-Brown nonlinear failure criterion and upper bound theorem of limit analysis,the three-dimensional collapse mode of surrounding rock induced by a concealed karst cave above a deep buried cavity was studied in this paper.The main research contents are as follows:(1)According to the mechanical mechanism and collapse mode of surrounding rock of the deep buried cavity beneath a concealed karst cave,the three-dimensional collapse mechanism of surrounding rock induced by a concealed karst cave above a deep buried cavity is constructed.By using Hoek-Brown nonlinear failure criterion and upper bound theorem of limit analysis,and combining with the principle of variational theory,the analytical expression of three-dimensional collapse surface of surrounding rock between concealed karst cave and deep buried cavity is calculated.(2)The difference method is used to calculate the numerical solution of the collapse surface curve of the surrounding rock at the top of the deep buried cavity when the analytical solution of the collapse surface of the surrounding rock cannot be obtained.The validity of the numerical solution of the equation of surrounding rock collapse surface calculated by the difference method is verified by comparing with the case of the existence of analytical solution.(3)According to the equation of collapse surface of surrounding rock derived from theory,the three-dimensional diagrams of collapse surface of surrounding rock induced by the concealed karst cave above a deep buried cavity under the action of different parameters is drawn,and the influence rule of single parameter variation on the collapse shape and scope of the surrounding rock at the top of the deep buried cavity is summarized.(4)The numerical model of concealed karst cave above a deep buried cavity was constructed by using the finite-difference software FLAC3D,and the numerical solution of surrounding rock collapse surface of concealed karst cave above a deep buried cavity was obtained by calculation.The theoretical analysis results under the same parameters are compared with the numerical simulation results,the correctness of the theoretical analysis is verified.(5)Based on the tunnel engineering which is located in karst area,the collapse shape and scope of surrounding rock induced by concealed karst cave above a deep buried cavity are calculated by the theoretical method and numerical simulation method which are proposed in this paper.It is proved that the theoretical method can be used to research the collapse mode and scope of surrounding rock induced by the karst cave in practical engineering.