Study On Mechanical Characteristics And Deformation Law Of Rock-sandwiched Columns In Small Clear Distance Highway Tunnel

The distance between the left and right tunnels of the small clear distance tunnel is relatively small,and there will be mutual interference between the two tunnels during construction.After the excavation of the first tunnel,the surrounding rock will gradually stabilize after the stress redistribution,however,after the excavation of the back tunnel,the surrounding rock,which had already become stable,will be disturbed again.Repeated disturbances will lead to a decrease in the stability of the surrounding rock,especially for shallow tunnels with small clear distance,which have poor stability of their own,after being disturbed many times,it will bring many disadvantages to the field construction.Because the thickness of rock pillar in small spacing tunnel is small,the stability and deformation of rock pillar between two tunnels often determine the stability and deformation of the whole tunnel.In view of this,based on the Xinjiu road tunnel in Jiulongpo District,Chongqing,this paper studies the mechanical characteristics and Deformation Law of the rock columns in the small clear distance highway tunnel by numerical simulation,the mechanical mechanism of the rock pillar in the tunnel with small spacing is revealed.The research results have certain theoretical value and practical engineering significance.The main research contents are as follows:(1)Through the statistics and analysis of the site monitoring data of Xinjiulu tunnel,the deformation and stress characteristics of the surrounding rock of the deep-buried tunnel and the shallow-buried tunnel are studied.The results show that the "Fulcrum" effect is obvious in shallow tunnel with small clear distance,and the "Fulcrum" effect is weakened in deep tunnel with small clear distance surrounded by pressure arch.(2)Using the software MADIS-GTS NX to establish the three-dimensional tunnel space model for analysis and calculation,in this paper,the lateral and axial settlement of small spacing tunnel under different buried depths are studied,and the mechanical characteristics of rock columns in deep small spacing tunnel and shallow small spacing tunnel are analyzed.The results show that when the depth of small spacing tunnel is small,the surface settlement curve presents a "W" shape.With the increase of the depth,the surface settlement curve gradually changes into a "U" shape,and the maximum deformation point of arch structure is located in vault,when the ground settlement at the middle rock pillar becomes the maximum point,the pressure arch has been formed.Therefore,the critical buried depth of the middle rock pillar can be used as one of the basis for dividing the shallow and deep buried tunnels with small clear distance.(3)Taking the rock pillar in the shallow-buried tunnel with small clear distance as the main research object,based on the investigation of the variation of the ground settlement,Vault settlement,invert deformation and lining stress of the tunnel under different reinforcing shapes and heights of the middle rock column,the optimal reinforcement method of the Middle Rock column is studied.The results show that the reinforcement of rock columns in shallow tunnels with small clear distance should take the shape of the vault of two tunnels as the boundary and reinforce to the ground surface,the optimal reinforcement mode of deep-buried tunnel is that the side wall of the two tunnels is the boundary and the reinforcement height is higher than the vault.