Research On Large Deformation Control Technology Of Soft Surrounding Rock In Xiejiapo Tunnel

With the continuous development of highway tunnels in China,there are more and more tunnels with weak surrounding rock in the planned and designed tunnels.However,there are many engineering problems during the construction of tunnel with weak surrounding rock,such as large deformation of surrounding rock,face collapse,arch collapse,etc.,which lead to rising project cost and delaying construction progress.Therefore,it is of great practical significance to study the excavation method and support technology in soft surrounding rock tunnel for ensuring the safety and quality of soft surrounding rock tunnel construction.This study takes Xiejiapo tunnel as the engineering background,based on the analysis of tunnel design method and construction scheme,the application effect of double-layer supporting structure in large deformation section of Xiejiapo tunnel is studied by combining theoretical analysis with field test.The main contents of this study are as follows:(1)This paper discusses the effect of the initial supporting structure on the tunnel with weak surrounding rock,and focuses on the mechanics of surrounding rock in the whole process of tunnel excavation,and the effect of each structure in the tunnel support system on the stability of the tunnel.This paper summarizes the stress variation law of each part of the weak surrounding rock and the primary support structure,and explores the interaction law between the two in different stages.The results show that:through rigid support to control the early deformation rate of surrounding rock,select the appropriate form of support to control the deformation of surrounding rock during excavation,it is in line with the deformation law of large deformation tunnel in weak surrounding rock.(2)According to the convergence-confinement method,the relationship between the surrounding rock and the supporting structure is analyzed.The double-layer supporting control technology is proposed through theoretical calculation,and the restraining effect of the double-layer initial support at different construction time on the surrounding rock deformation is analyzed.The results show that:the double-layer initial support can provide enough support resistance for the tunnel surrounding rock plastic deformation when the tunnel surrounding rock condition is very poor and the ground stress is small.(3)Combined with the actual situation,a 3D model of Xiejiapo tunnel is established using MIDAS/GTS numerical analysis software.The influence of single-layer primary support structure and double-layer primary support structure with different construction time on surrounding rock displacement and stress during tunnel construction is analyzed.The results show that:compared with the numerical simulation results of single-layer initial support and double-layer initial support,it can be seen that the effect of double-layer initial support on restraining tunnel displacement is obvious when the surrounding rock is poor,and the tunnel buried depth is shallow,the ground stress is not high.The final displacement of the tunnel with delayed double-layer initial support is larger than that with double-layer initial support at the same time,but the former is better in improving the stress of tunnel surrounding rock and the stress state of tunnel support structure.(4)The deformation monitoring of large deformation section of Xiejiapo tunnel is carried out,and the influence of different initial support forms and different construction time of two-layer initial support structure on deformation value and deformation rate of tunnel surrounding rock is analyzed.At the same time,the results of field measurement and numerical simulation are compared and analyzed to verify that the numerical simulation method established in this paper is feasible and effective.Finally,the monitoring and measurement data are used to guide the construction and ensure the construction safety.