Study On Stress Characteristics Of Tunnel Lining In High Ground Stress Fault Fracture Zone

As the Belt and Road strategy has been applied,the economic development in Western China has hitherto unknown opportunities,along with the rapid rise of transportation construction.But western China is mostly mountainous area.Due to high mountains and deep valleys,frequent geological movements,tunnel construction often faces the problems of high ground stress and fault fracture zone.As a common geological structure,fault fracture zone has the characteristics of poor stability and large dispersion.Considering the influence of high ground stress,it is very easy to cause instability of surrounding rock and damage of support structure,which seriously threatens tunnel construction and operation The security of the system.In this paper,the physical model test and numerical simulation are combined to explore the stability of surrounding rock and the stress and safety of lining in high geostress fault fracture zone tunnel,the main contents and conclusions are as follows:(1)According to the engineering background and the similarity theory,the physical model test with the similarity ratio of 1:30 is carried out for the tunnel in the high ground stress fault fracture zone,and studies the tunnel in fault fracture zone with high geostress by using physical model test,and studies the stress distribution of surrounding rock under different lateral pressure coefficient and geostress of physical model The lateral pressure coefficient with the lowest safety is obtained,and the stress characteristics and safety failure of lining structure under gradually increasing load are obtained;(2)The Voronoi polygons with different sizes and random distribution are generated by V_C++programming to simulate the fault fracture zone with uneven size of rock blocks,and the graphics are imported into the discrete element software UDEC by the command of crank.Then the uniaxial compression test is carried out in the software to obtain the numerical simulation parameters of rock mass materials.Finally,the numerical simulation of the model test conditions is carried out and the results are compared with the model test results,It is found that the two laws are basically the same,which fully verifies the correctness and feasibility of the simulation,and provides a basis for the expansion analysis of tunnels in high geostress fault fracture zone,the side arch foot near the fault fracture zone is the most disadvantageous;(3)Through numerical simulation,the tunnel in fault fracture zone under different in-situ stress conditions is studied with lateral pressure coefficient and buried depth as variables.The results show that the low lateral pressure coefficient is not conducive to the formation of pressure arch,and the self stability of surrounding rock is poor,which is unfavorable to the stability of surrounding rock and the stress of lining.When the surrounding rock has self stability ability,the increase of lateral pressure coefficient and the increase of tunnel buried depth are both negative The safety factor of lining structure is lower than the standard value according to the sequence of arch foot,arch bottom,arch crown and arch waist;(4)Through numerical simulation,the influence of different forms of fault fracture zone on the stability of surrounding rock,lining stress and safety is explored,taking the distance between fault fracture zone and tunnel,the thickness and inclination of fault fracture zone as variables.The results show that:with the increase of the distance or the decrease of the thickness of the fault fracture zone,the stability of the surrounding rock will be improved,which is conducive to the stress and safety of the lining.This trend is most obvious when the distance is less than 0.5 times of the tunnel diameter or the thickness is less than 0.75 times of the tunnel diameter.The increase of the inclination angle will cause the bias load,the stress of the lining first increases and then decreases,and the change of the safety factor is opposite.