Research On Segment Safety And Control Measures Of Subway Shield Tunnel Crossing Karst Area

With the continuous development of Chinese economy and society,the demand for infrastructure construction is also increasing,and shield tunnels have been widely used in urban construction.However,the complex geological conditions of karst have brought great challenges to the construction of shield tunnels.Therefore,it is of great significance to carry out the safety analysis of shield tunnel segments through karst strata and the research on control measures in karst areas.In this paper,combined with the karst distribution characteristics of Shenzhen Metro Line 16,relying on typical shield intervals,based on on-site engineering monitoring and analysis,and using numerical calculation methods,a mechanical calculation model for shield tunnels passing through karst areas is established,and the size and size of the central karst cave,karst cave The influence of the distance from the tunnel,the relative position of the cave and the tunnel on the deformation of the shield segment,using the ellipse eccentricity analysis method,studied the deformation characteristics of the segment caused by the shield tunnel passing through the karst area;The deformation of the segment was predicted,and the feasibility and effectiveness of the established BP neural network model were verified;the numerical calculation method was used to explore the effect of karst grouting reinforcement on the karst cave location,karst size,distance between karst and tunnel,and karst formation.The influence of the change of mechanical parameter characteristics on the deformation of the shield segment,the plastic zone of the surrounding rock,and the stress of the shield segment,the grouting construction technology and the selection of grouting materials were analyzed,and the cement slurry and cement mortar and the grouting filling degree were analyzed.The difference analysis of the grouting treatment effect was studied and evaluated through the actual engineering case.The main research conclusions are:(1)When the shield tunnel passes through the karst area from above and below,the central karst cave has a soil arch effect on the shield tunnel to a certain extent.The larger the diameter of the central karst cave,the stronger the soil arch effect.The smaller the eccentricity of the ellipse,the more round the shape of the ellipse;the greater the distance between the cave and the tunnel,the weaker the soil arching effect,the greater the eccentricity of the deformed shield segment,and the flatter the ellipse.When the shield tunnel passes through the karst area from the side,45 degrees upward and 45 degrees downward,the central karst cave will increase the deformation of the tunnel.The larger the diameter of the central karst cave,the greater the deformation of the shield tunnel segments.The larger the eccentricity of the deformed ellipse,the flatter the elliptical shape;the larger the distance between the cave and the tunnel,the smaller the deformation of the shield tunnel segment,the smaller the eccentricity of the deformed ellipse,and the smaller the elliptical shape.tends to be more round.(2)The grouting reinforcement of karst can reduce the settlement of the surrounding rock,improve the uplift of the shield tunnel segment vault when passing through the bottom cave,and reduce the settlement of the shield tunnel segment vault when passing through the top cave and side cave,especially greatly reducing the horizontal displacement of the shield tunnel segment when passing through the side karst cave.Compared with before grouting reinforcement,the distribution range of the plastic zone of the surrounding rock is reduced after grouting in the karst cave,and the effect of improving the plastic zone of the shield tunnel passing through the side karst cave is particularly significant.Under different karst sizes,different distances between karst tunnels,and different mechanical parameters of karst formations,after grouting reinforcement,the maximum principal stress of shield tunnel segments passing through karst caves increased slightly,and the maximum principal stress of shield tunnel segments passing through karst formations increased slightly after grouting reinforcement.Both stress and vertical shear stress are reduced.(3)In the analysis of the difference between karst grouting materials and grouting filling degree,the settlement of cement mortar segment vault is smaller than that of grouting grouting;The larger the vertical displacement of the arch bottom,the greater the amount of uplift,and the indirect reaction is that the possibility of the shield machine falling head during construction is reduced.By comprehensively using grouting record analysis,drilling coring and geophysical analysis,the test results before and after karst grouting are compared and studied.The results show that the filling effect of the project is good,which meets the safe construction requirements of shield tunneling.