Studyon The Stability Of Surrounding Rock And Safetythickness For The Water-filling Cast Cave In Front Of The Tunnel

Based on the water filling cave in front of the tunnelas the main research object.The development characteristics and water inrush pattern of karst cave are summarized.Numerical simulation is the main research method,the stability of surrounding rock is affected by the karst cave in front of the tunnel in various working conditions were analyzed.Relying on Xie-ma tunnel for engineering,the model test was used to simulate the specific conditions and the numerical simulation was used to verify the analysis,the information change law of the water inrush process and surrounding rock physical field was mastered.The numerical simulation results were further analyzedand the safe distance of tunnel construction under different working conditions is obtained,andthe following main conclusions were obtained.(1)The development characteristics of karst caves were studied from four aspects:formation lithology,geological structure,groundwater dynamic characteristics,climate and geomorphology.The developmental stages and spatial distribution of karst caves are summarized.The typical cases of karst water surge in dozens of tunnels in recent years were statistically analyzed.The karst caves are classified in terms of morphology,disclosure and filling(2)The numerical model of the water-filled cavern in front of the tunnel was established.The surrounding rock stability of the water-isolating rock mass in front of the tunnel is analyzed by three factors:the water pressure of the cave,the size of the cave and the buried depth of the tunnel.The variation characteristics of surrounding rock displacement under different factors and the stress evolution law of tunnel surrounding rock are studied.(3)The failure modes and the analysis methods of rock column instability are explored.Combined with numerical simulation,a new criterion for water inrush in karst caves is presented.plastic zone penetration,low pressure point of pore water,maximum(small)main stress unloading point.The minimum safe thickness range of rock mass at different factor levels is given.Combined with the minimum safe thickness of surrounding rock under various factors,univariate and multivariate regression analysis was carried out.The mathematical prediction model of the minimum safe thickness under the single factor and the multiple regression equation of the minimum safe thickness under the combined action of multiple factors are given.It provides a theoretical reference for calculating the minimum safety thickness of similar projects(4)Relying on xie-ma tunnel as an engineering example,a test system for water inrush model of large buried deep-high water pressure tunnel was developed,the model test of water inrush disaster evolution of water-filled karst cave in front of tunnel was carried out.Multiple physical information is set up during the excavation of key monitoring section monitoring model.The evolution of stress,displacement and seepage pressure information of surrounding rock was studied.At the same time,the engineering geological information of the test section is combined with numerical simulation verification.The variation rule of multifield information in numerical simulation is basically consistent with the model test results.The three stages of water conduction crack initiation,crack propagation and crack penetration caused by water inrush in the karst cave are defined.The penetration thickness of the surrounding rock in the front of the tunnel is given.lt can be used as a theoretical reference for the wall rock thickness retaining of the karst cave in front of similar tunnel project palm...