Study On Calculation Method Of Foundation Settlement Of Karst Tunnel

In recent years,with the highly operation demand of China's transportation industry,The high-speed railway business has been developing vigorously.Many railway tunnels have been built in the southwest area where the karst stratas are extremely developed.The karst geological hazards have posed a great challenge to the tunnel construction and operation and maintenance.In view of the uncertainty of karst development and the complexity of karst tunnels,the current research on karst tunnels is far from enough to meet the needs of the construction.Therefore,the large-scale karst of Changqingpo tunnel in Yun-Gui railway is taken as the research object in this paper,and the generalized model of filling karst tunnel is established.The influence of the boundary range of the filling karst on the settlement of the tunnel foundation under the load of the train was studied by using the FLAC3D calculation software.Based on the settlement calculation of the open foundation,the calculation method of the settlement of the tunnel foundation was obtained through the data analysis.The main contents of the paper are as follows:(1)Based on the previous research data,this paper summarizes the current situation of the study on the influence of the thickness and stability of karst roofs,the size and location of karst on the tunnel engineering.(2)Take the large-scale karst of Changqingpo tunnel as the rearch background,the spatial relationship between karst and tunnel is analyzed and summarized as three models.Finally,the karst tunnel generalization model is established.(3)The karst tunnel analysis model was established by using the numerical calculation software,and the influence of the karst boundary on the settlement of the tunnel bottom is studied.The results show that the influence range of the left and right boundary is 2d(d is the tunnel diameter),the influence range of the lower boundary is 3d,the influence range of the upper boundary is 1d;When the karst is located below the tunnel base,the safety thickness of the tunnel floor is not less than 5m;The lateral karst will cause stress concentration in the surrounding rock of the tunnel,and the closer the distance,the greater the stress concentration.(4)When the karst exists in the limited range of the tunnel plane,it is necessary to integrate the karst boundary parameters to study its comprehensive influence on the settlement of the tunnel,The final simulation results show that the maximum influence range of the upper axis is 1.6d and the minimum influence range is-0.5d;The minimum influence range of the lower axis is-3.Id.When the lower boundary of the karst exceeds the base surface,the influence of karst on the loading of the tunnel base is small,but the influence on the surrounding rock of the tunnel can not be ignored.(5)Based on the numerical simulation results,the basic calculation method of karst tunnel foundation settlement considering the influence of karst boundary is established by 1stOpt data fitting software,and the graphical programming software Lab VIEW is used to realize the interconnection and programming of the calculation process.According to the exanmple of a specific karst tunnel,this paper uses the base settlement calculation program to compare with the calculated value of settlement in the example,and verify the rationality of the proposed method.