Study On Deformation Law And Construction Parameter Optimization Of Pile And Plate Composite Foundation Under Shield Tunneling

With the rapid development of urban rail transit,the utilization rate of ground space tends to be saturated,and cross-crossing projects such as subway tunnel under construction of highspeed railway appear.Shield construction of subway tunnel will cause disturbance to surrounding structures and foundation,which will affect the normal operation of high-speed railway under construction.In order to reduce the impact of subway shield construction,and meet the requirements of bearing capacity of high railway foundation and foundation under construction.Taking Fuzhou Metro Line 5 underpassing Fuzhou-Xiamen high-speed railway section as a supporting project,this paper adopts the methods of theoretical analysis,numerical simulation and field monitoring to study the deformation law of pile-plate composite foundation under shield construction and parameter optimization of shield construction,aiming at the particularity of high-speed railway pile-plate composite foundation under construction under curved shield tunnel.The main research contents and results are as follows:(1)Based on the actual engineering background,the influence mechanism of shield construction on ground soil and pile-plate composite foundation is analyzed.The results show that the formation deformation under shield construction mainly has five development stages,in which the shield construction will have a significant impact on the vertical and horizontal deformation of pile foundation,resulting in upward warping deformation at both ends of the bearing plate,and transverse bending deformation of the bearing plate directly above the tunnel.(2)Aiming at the subway shield tunneling under construction of high-speed railway pileplate composite foundation,the finite element model of "shield tunnel-pile plate composite foundation-high railway foundation under construction" is established,and the influence of shield construction on the deformation of pile-plate composite foundation under different excavation sequence and different geological conditions is analyzed.The results show that the construction mode of right line followed by left line has little influence on the deformation of pile and plate composite foundation,and setting isolation pile can effectively reduce the deformation at both ends of the pile and plate structure.The settlement and uplift of the pile plate structure are mainly located in the upper part of the tunnel when the cohesive soil layer is penetrated,while the deformation of the two ends of the bearing plate above the tunnel is larger when the sandy soil layer and the pebble layer are penetrated.(3)In order to explore the mutual influence of shield tunnel construction and crossconstruction of high-speed railway under construction and the control effect of pile-plate composite foundation,the influence law of subway shield construction on the deformation of subway tunnel and the upper high railway foundation,and the influence law of high-speed railway construction under construction on the deformation law of subway shield tunnel and pile-plate composite foundation are studied.At the same time,the deformation and stress characteristics of composite foundation with or without pile and plate are compared and analyzed.The results show that the settlement of the upper high railway foundation caused by shield construction is small,and its deformation is mainly distributed on both sides of the subgrade and the area directly above the double-track tunnel.With the increase of subgrade filling height,the deformation of pile-plate composite foundation and shield tunnel increases gradually.The maximum settlement of surrounding rock is reduced by 67.74%,and the maximum uplift displacement is reduced by 17.77%.Moreover,the stress of tunnel segments can be effectively dispersed.The axial force in the area directly below the subgrade is larger,and the shear at the joint of pile foundation and bearing plate is larger.(4)In order to reduce the influence of shield construction on the deformation of pile and plate composite foundation and high railway foundation under construction,the shield construction parameters such as tunneling pressure,grouting reinforcement and excavation sequence are optimized.The results show that the change of tunneling pressure has the most significant influence on pile and plate composite foundation and high railway foundation under construction.Meanwhile,synchronous grouting should be ensured as far as possible to ensure the dense filling.It is more reasonable to adopt the shield tunneling method of right line first and left line second in double-line tunnel.(5)The ground settlement,subgrade settlement,subgrade soil compressive stress and tunnel deformation monitored on site are compared with the theoretical calculation results.The results show that: from the field monitoring data,the shield construction makes the surface settlement increase,at the same time,the soil pressure and the soil pressure change rate will increase rapidly when each layer of subgrade is filled,and the soil pressure under the subgrade is larger.The maximum cumulative deformation of the arch roof is 4.57 mm,the maximum deformation of the arch bottom is 4.38 mm,and the maximum headroom convergence is3.83 mm,which is smaller than the calculated value of the model and within the range of the control value.The transverse deformation and longitudinal deformation of the surface calculated by the model are basically consistent with the deformation law of the field monitoring data.