Study On The Influence Laws Of The Existing Tunnel Induced By Construction Of The Overlapped Soft Rock Tunnels With Small Clear Spacing

It is of great significance to study the influence law of existing tunnel and surface deformation induced by the construction of cross tunnels with small clear distance.This paper takes the intersection of a vehicle line and the positive line of Nanning Metro Line 1 as the background,and uses the methods of theoretical analysis,theoretical calculation,numerical simulation and on-site monitoring to carry out research.The main contents and conclusions are as follows:(1)The influence area of adjacent tunnel construction is given,and the deformation mechanism and force characteristics for eight different approaches are analyzed.The main factors affecting the existing tunnels and surface deformation induced by the construction of cross tunnels are:engineering and hydrogeological conditions,existing tunnel conditions,new tunnel conditions,and the spatial relation between new tunnels and existing tunnels.(2)Based on the intersection of the Nanning Metro Line 1 exit line and the mainline interval small-span distance tunnel,a three-dimensional model is built using FLAC software.The influence law of existing tunnel lining and surface deformation induced by top-through and bottom-through tunneling method is simulated and forecasted.The results of FLAC analysis show that the surface settlement induced by the construction of top-through tunneling method is larger than the bottom-through tunneling method.The deformation of existing tunnel lining induced by the bottom-through method is greater than that of the top-through method.The analysis results show that the amount of ground settlement induced by cross-tunnel construction and the value of existing tunnel deformation are extremely sensitive to the spatial location of the tunnel.The range of plastic zone of surrounding rock caused by bottom-through and top-through tunneling method is equivalent.Some suggestions are put forward for the construction of this project by the method of top-through tunneling method.(3)The vertical displacement solution of the existing tunnel lining induced by the bottom-through method construction is obtained by the two-stage displacement method,and the sensitivity of relevant parameters is analyzed.The tunnel intersection angle was the most significant in these factors.The calculation method for inducing the vertical deformation of the existing tunnel lining under the condition of considering the tunnel curvature is presented.The application of the program is applied to the specific project.(4)The control measures for the full section grouting reinforcement of the steel flower tube and the final construction plan for the construction of the left line,right line and mined tunnels in sequence are proposed.The FLAC simulation method is used to evaluate the feasibility of surface and lining deformation control measures induced by overlapping tunnel construction.The results show that the maximum deformation of the ground surface is reduced by about 38.2%compared with no control measures and the scope of surface vertical deformation and crown deformation is reduced by about 33.3%.(5)The measured results show that the ground settlement value is significantly affected by the space location relationship between the tunnels.The maximum value occurs at the position directly above the center of the tunnel in the near-parallel region of the three tunnels.The engineering practice shows that the proposed cross-tunnel reinforcement measures and the final construction plan are reasonable and feasible,which have good effect on controlling surface deformation and can provide reference for similar projects.