Analysis Of Construction Stability Of Qingdao Metro Cross-sea Tunnel Crossing Fault Fracture Zone Under Fluid-Solid Coupling Effect

With the development of the national economy and technology and the needs of national strategies and urban development,the construction of the undersea tunnel is in full swing.It not only effectively shortens the distance between the two sides of the bay but also greatly eases the traffic pressure.The meaning is self-evident.The surrounding rock of the subsea tunnel is always in a state of high pressure head and unlimited seawater replenishment,so groundwater is an important consideration;at the same time,the disturbance caused by construction under the fluid-solid coupling effect will damage the surrounding rock of the tunnel,and when the tunnel When crossing the fault fracture zone,it will aggravate the degree of fracture of the surrounding rock,further increase the possibility of tunnel instability and damage,and increase the construction risk.This article takes the cross-harbour tunnel in the section of Wawuzhuang Station to Guizhou Road Station in Qingdao Metro Line 1 as the research object.Through theoretical analysis,numerical simulation and on-site monitoring methods,the fluid-structure coupling effect and crossing during the construction of the subsea tunnel The stability of the fault fracture zone is studied,and a targeted stratum reinforcement design is proposed.The main research work of this article is as follows:(1)Theoretical study on fluid-structure coupling of subsea tunnel This paper analyzes the basic theory and equations of fluid-solid coupling in subsea tunnel engineering,and analyzes the mathematical model of the stress field of surrounding rock under fluid-solid coupling and the seepage field under coupled state,and the Mohr-Coulomb strength used by finite difference software to solve the stress of surrounding rock Criterion;analyzes the change of permeability during rock damage and destruction,establishes the evolution model of permeability characteristics and analyzes its evolution law,in order to provide a theoretical basis for the numerical simulation calculation of fluid-structure coupling considering the permeability change of surrounding rock in the subsea tunnel.(2)Analysis of the seepage field of the surrounding rock of the Qingdao Metro Line 1 subsea tunnel.In this paper,the basic theory of the mirror image method is used to derive the analytical solution of the seepage field of the single-hole subsea tunnel,and its accuracy is verified.Through the analysis of the influence parameters,it is found that improving the initial support anti-seepage performance and increasing its thickness can effectively reduce the amount of tunnel water inflow,but the corresponding increase The water pressure on the lining;increasing the thickness of the grouting ring and reducing the permeability coefficient will reduce the inflow of the tunnel and the water pressure after the initial support in an inverse proportional function;using the analytical formula of the seepage field in this paper to the Qingdao Metro Line 1 The amount of water inflow through the subsea tunnel through the fault fracture zone is analyzed,which provides a theoretical basis for grouting and strengthening the surrounding rock of the subsea tunnel through the fault fracture zone.(3)Stability analysis of subsea tunnel crossing fault fracture zone under fluid-solid coupling effect.The tunnel excavation under the fluid-solid coupling effect has caused the pore water pressure around the tunnel to always show a downward trend,and the decreasing range increases from the upper part of the tunnel to the lower;and the excavation construction makes the permeability of the surrounding rock and the coefficient of permeability increase.Compared with the surrounding rock with better lithology;when the tunnel passes through the fault fracture zone,the deformation value of the monitoring point is taken through numerical simulation,and the deformation of the surrounding rock around the tunnel is found to be too large,with a maximum deformation of 16.72mm,which is exceeded in many places.The early warning value allowed by the standard requires effective reinforcement measures for tunnels passing through bad geological sections.(4)Grouting reinforcement and construction monitoring analysis of the surrounding rock of the subsea tunnel crossing the fault fracture zone.A targeted grouting reinforcement design is proposed for the tunnel passing through the fault fracture zone;comparing the simulated data with the measured data,it is found that the change trends of displacement and surrounding rock pressure are approximately the same,and the gap between the simulated value of the deformation around the cave and the measured data is the same No more than 0.5mm,and the pressure value of the surrounding rock extracted after the convergence of the numerical simulation is almost the same as the measured value,thus proving the feasibility and accuracy of the numerical simulation method;after the actual project adopts the grouting reinforcement design,the maximum settlement of the vault The value is-0.9mm,and the maximum clearance value is 2.6mm,which does not exceed the warning value required by the specification.The rock deformation around the cave is effectively controlled,which proves the effectiveness of grouting reinforcement.