The Collapse Mechanism Of Rock Mass Above A Highway Tunnel Induced By A Concealed Karst Cave In Karst Region

With the implementation of One Belt One Road strategy,a large number of tunnel projects are constructed in the karst areas of western China.When the distance between the proposed tunnel and the karst cave is too close,the middle sandwiched rock layer between the karst cave and the tunnel will easily collapse under the action of blast wave,which will bring great threat to the life safety of tunnel construction personnel.In view of this phenomenon,based on the Hoek-Brown failure criterion and the upper limit theorem of limit analysis,this paper studies the collapse failure mode and the minimum safe distance between the karst cave and the surrounding rock of the deep buried highway tunnel with hidden karst cave at the top.The main research contents are as follows:(1)Based on the failure characteristics of surrounding rock collapse in the deep buried highway tunnel with hidden karst cave at the top,the upper limit failure mechanism for this failure form is constructed.Using Hoek-Brown failure criterion and upper limit theoren of limit analysis,the analytical expression of failure surface equation of surrounding rock collapse at the top of deep buried highway is derived;(2)Based on the analytic equation of collapse failure surface of surrounding rock induced by karst cave at the top of highway tunnel,the shape of collapse surface of surrounding rock at the top of deeply buried highway tunnel was drawn,and the influence of different parameters on the shape and collapse range of collapse surface was analyzed;(3)Based on the law that the shape of collapse surface of surrounding rock at the top of a deep-buried highway tunnel changes with the distance between the karst cave and the tunnel,the minimum safe distance between the karst cave and the tunnel is defined,and the calculation formula of the safe distance is given;(4)Build the deep buried highway tunnel of existence of concealed karst cave above the numerical calculation model,by using the finite difference software FLAC3D to simulate the excavation process of the tunnel,got the top of the existence of concealed karst cave tunnel surrounding rock landslide damage numerical solution,and compared with theoretical solution obtained by upper-bound method,to verify the effectiveness of the upper limit method to calculate the results;(5)On the basis of the observed geological data of highway tunnel with concealed karst cave of on the top,adopt the method of the tunnel at the top of the wall rock landslide failure process are calculated,the top tunnel surrounding rock of the cave and analytic equation is obtained and compared with numerical simulation results,the results show that the method can be used in practical engineering of concealed karst cave induced collapsing destruction of surrounding rock of highway tunnel roof is calculated.