Study On Reasonable Distance Of Tunnel With Small-distance In Soft Surrounding Rock And Reinforcement Technology Of Medium Rock Wall

The "Zhitong Expressway Tunnel Construction Safety Risk Overall Assessment Report"pointed out that "the Zhaizijie Tunnel is a small net distance tunnel,the thickness of the rock layer in the partition wall is small during excavation,the thinnest place is less than 1 meter,the construction is difficult,the construction safety risk is high,it is recommended to change to a continuous arch tunnel,which is conducive to construction." "Taking the Zhitong(Xiangqianjie)high-speed Zhaizijie Tunnel as the background,the finite element analysis software MIDAS GTS NX is used to establish two tunnel type numerical models of small net distance tunnels with different medium rock wall thicknesses and arch tunnels with different middle partition wall thicknesses under weak surrounding rock(V-class surrounding rock),and through the comparative analysis of the construction mechanical characteristics of the two tunnel types,the reasonable net distance of the small net distance tunnel under the V-class surrounding rock is determined." Combined with the difference in force between the arch tunnel and the small net distance tunnel,a new reinforcement measure for the middle rock wall is proposed,which has guiding significance for the dynamic design and construction of the tunnel.The main research content of this paper includes the following aspects:(1)Based on the mechanical theory of tunnel structure,finite element method,elastoplasticity theory,etc.,the stress characteristics of the surrounding rock of the small net distance tunnel are analyzed,and the numerical simulation of the zhaizijie tunnel is carried out based on its stress characteristics.(2)The construction process established by using MIDAS GTS NX finite element software adopts CRD construction method to build a variety of clear distance small net distance tunnels and arch tunnels under the geological conditions of the Zhaizijie tunnel.Comparing the tunnel vertical and horizontal displacement,surrounding rock stress and initial support structure stress under different tunnel types of the same middle rock wall thickness and different middle rock wall thicknesses of the same tunnel type,the minimum reasonable net distance value of the small net distance tunnel under the actual project is 0.5B.(3)In order to better strengthen the rock wall in the small net distance tunnel,starting from the comparison of the force deformation of the small net distance tunnel and the continuous arch tunnel,the steel arch+grouting combination reinforcement measures are proposed,and the reinforcement of the pull prestressed anchor rod+grouting combination is comprehensively compared with the special construction plan of the Zhaizijie Tunnel,and the combined reinforcement measures of the steel arch+grouting combination of the small net distance tunnel under the weak surrounding rock can be more effectively controlled by the vertical displacement of the tunnel and the middle rock wall.