Study On The Influence And Measures Of Shield Tunneling Through Railway Frame Structure In Sandy Pebble Stratum

Based on theoretical analysis,numerical simulation and field monitoring and other research methods,the paper makes a deep discussion and analysis of shield tunneling construction technology under the geological conditions of sand gravel layer.The main research work and research results are as follows:(1)Taking the project as the background,through the analysis of the engineering characteristics of the shield tunneling through the railway frame bridge in the sandy pebble stratum in the project area,the preliminary selection of shield parameters and the formulation of shield construction measures are targeted to prepare for the subsequent analysis and parameter optimization.(2)The numerical simulation of the primary scheme of shield is carried out,and the overall deformation law of the model,the influence law of the ground settlement,the influence law of the lower frame bridge and pier cap,and the influence law of the slope safety are analyzed.The research shows that the tunnel excavation will cause longitudinal and transverse"settlement trough";the maximum displacement of the frame bridge structure occurs in the middle and back lower floor,and the minimum displacement occurs in the left side wall edge of the frame structure.The settlement of the whole frame structure is characterized by large in the middle,small on both sides,small on the left and large on the right;stress concentration occurs at the joint of pier and bearing platform;the shear stress at the top of pile is large,and the shear stress at the bottom of pile is small,while the pile stress at both sides is larger than that at the middle;the deformation at both sides of slope is small,and the middle part is large.The overall deformation and stress caused by the construction of the preliminary selection scheme of shield are small,so the construction is relatively safe.(3)On the basis of the primary scheme,the influence rules of shield construction under different driving pressure,Jack force,grouting pressure and excavation footage are analyzed and optimized.The analysis shows that,with the increase of driving pressure,the rebound of the face along the opposite direction of excavation will decrease.Considering the stress of the face and the deformation of the face,the driving pressure is 120 kN/m~2;increasing the jack force to some extent can reduce the maximum principal stress of the small pipe piece,and considering the deformation peak value of the pipe piece,the jack force is 110 kN/m;the increase of grouting pressure can reduce the maximum principal stress value of segment.For segment deformation,the influence of grouting pressure change on segment deformation can be ignored.Therefore,in the construction,the larger grouting pressure is 170 kN/m2,and the excavation footage is 3.2 m,the overall deformation of the model is the smallest,and it plays a good role in controlling the differential settlement of the surface.The settlement difference of the surface is controlled within 0.28 mm,making the settlement more balanced.The excavation footage of the optimized scheme is 3.2 m.Through the optimization of the primary scheme,the safety of shield construction is ensured.(4)The plan of field monitoring is made,the data of field monitoring is sorted out and analyzed,and the influence laws of ground settlement,pier deformation,building settlement and segment deformation in shield construction are studied.Through the comparison between the numerical simulation results and the field monitoring results,the results show that the laws of stress and deformation of the upper soil and structure caused by the shield construction in the numerical simulation are consistent with the actual situation,which verifies the feasibility of the numerical simulation results.