Study On Construction Mechanical Behavior Of Water Rich Shallow Buried Multi Arch Tunnel

Based on the water rich shallow buried multi arch tunnel project in the entrance and exit section of an urban rail transit in Northeast China,the influence of fluid structure coupling on the construction of water rich shallow buried multi arch tunnel is studied and analyzed by means of theoretical analysis,numerical simulation and field measurement;And based on flac3d5 0 finite difference software numerically simulates and analyzes the four influencing factors of shallow buried multi arch tunnel under different construction conditions of tunnel under fluid structure coupling,such as tunnel excavation scheme,saturation of surrounding rock,excavation step of tunnel construction and excavation distance between left and right tunnels of multi arch tunnel;Relying on the finite difference software flac3d5 0 combined with the grey correlation principle,the sensitivity analysis and Research on the specific construction condition parameters affecting the surrounding rock deformation of water rich shallow buried multi arch tunnel under different construction conditions(surrounding rock saturation,construction excavation step,excavation stagger of left and right tunnels)are carried out.The main results and conclusions of the paper are as follows:(1)Through theoretical analysis and comparison of mechanical characteristic time t_s and fluid diffusion timet_c,it can be seen from the calculation that it is within the range of,so the tunnel excavation adopts the method of complete fluid structure coupling for fluid structure coupling calculation;The numerical simulation method is used to compare and analyze the final cumulative settlement of the vault of the left and right tunnels,the final displacement of the convergence around the tunnel,the stress characteristics of the initial support and the area and distribution of the plastic zone of a water rich shallow buried multi arch tunnel in Northeast China.It is obtained that under the condition of fluid structure coupling,the deformation of surrounding rock,the stress of initial support and the area of plastic zone of tunnel are larger than those without considering fluid structure coupling.The accuracy of the numerical model considering fluid structure interaction is verified by comparing the numerical simulation results with the measured data.Therefore,the fluid structure interaction must be fully considered in the water rich shallow buried multi arch tunnel project.(2)On the basis of considering the fluid structure coupling effect,the control variable method is used to simulate and analyze the four influencing factors of the tunnel excavation scheme,the saturation of surrounding rock,the excavation step of tunnel construction and the excavation distance between the left and right tunnels of the multi arch tunnel under different construction conditions.Combined with the actual situation of the tunnel project,it is suggested to adopt the three-step excavation method of core soil;In order to ensure safety during excavation,waterproof and drainage work shall be done in time to prevent softening of tunnel surrounding rock caused by excessive saturation of surrounding rock;It is suggested that the tunnel excavation step should be 2m;The excavation spacing between the left and right tunnels of the tunnel is recommended to be 8m.(3)Relying on the finite difference software flac3d5 0 combined with the grey correlation principle,the sensitivity analysis and Research on the specific construction condition parameters affecting the surrounding rock deformation of water rich shallow buried multi arch tunnel under different construction conditions(surrounding rock saturation,construction excavation step,excavation stagger of left and right tunnels)are carried out.The sensitivity of each influencing factor is obtained through matrix calculation,and the sensitivity of each influencing factor is compared.It is concluded that among the three influencing factors of the final cumulative settlement value of the arch crown of the water rich shallow buried multi arch tunnel under different construction conditions and the final displacement value of peripheral convergence,the construction excavation step has the greatest influence on the final displacement value of peripheral convergence of the tunnel,followed by the surrounding rock saturation,and finally the excavation offset of the left and right tunnels.Therefore,in the process of tunnel excavation,we should focus on the factors of construction excavation step distance and surrounding rock saturation,reasonably control the construction excavation step distance and do a good job in waterproof and drainage.