Deformation Mechanism And Prevention And Control Measures Of Layered Surrounding Rock In Soft Rock Tunnel

Due to the complex geological environment,hydrogeology and stratum lithology conditions in the central and western regions of China,a large number of fold rock structures have been formed in the southwest region under the action of geological evolution for tens of thousands of years.This means that in the coming decades,the tunnel group constructed in the central and western regions of China will face a series of major problems,such as "extremely deep burial,ultra-high ground stress,high water pressure,frequent geological secondary disasters,obvious bedding through the strata,and poor rock mechanics properties".With the emergence of the above problems,the stability analysis of layered soft surrounding rock and the stress characteristics of supporting structure of deep buried tunnel need further study.Supported by the National Key Reserach and Development Program of China(2018-JKGF-2083),this paper takes deep buried layered soft rock tunnel as the research object,and carries out in-depth research on the large deformation failure mechanism and large deformation prevention and control measures of layered soft rock tunnel in high in-situ stress area.The main work and research results are as follows:(1)Carry out uniaxial loading and unloading,uniaxial compression and Brazilian splitting tests of carbonite Slate,as well as XRD test of rock mineral composition.In addition,the layered composite rock mass is also made,and the uniaxial compression test and acoustic wave velocity test are carried out to analyze the mechanical properties and failure characteristics of the layered composite rock mass,revealing the influence of the layered structure on the mechanical properties and failure characteristics of the layered rock mass.(2)Based on the study of failure characteristics and mechanical properties of layered rock mass,the suitability of large deformation failure mechanism and different constitutive relationships of layered soft surrounding rock was studied.The failure of layered soft rock tunnel is mainly due to the deformation and failure of layered surrounding rock under the action of high in-situ stress,and the special deformation mode induced by high in-situ stress is jointly controlled by the coupling action of multi-factors such as strength of layered rock mass,dip angle of strata,stress direction and Angle of strata.(3)The asymmetric large deformation of deep buried layered soft rock tunnel and the mechanical characteristics of asymmetric surrounding rock are studied.FLAC3 D finite element simulation software is used to simulate different working conditions,revealing the influence of buried depth,bedding Angle,lateral pressure coefficient and other factors on the asymmetric large deformation of surrounding rock.It is found that the lateral pressure coefficient and buried depth are proportional to the amount of asymmetric large deformation,and the bedding Angle mainly affects the position of large deformation.(4)Based on the research results of large deformation mechanism of surrounding rock,the prevention and control measures of large deformation of tunnel in layered soft surrounding rock are studied.The conclusion is that asymmetric bolt support and reasonable steel arch spacing have good control effect on large deformation support of layered soft rock.The principle of short excavation,strong support,early support and early closure is adopted.In addition,in addition to high-strength support for the parts with the maximum deformation of large deformation,enough attention should be paid to the deformation of the arch waist,and the supporting structure should be reinforced appropriately.