Study On Deformation Characteristics And Control Technology Of Initial Support In Bench Method Construction Of Tunnel Crossing Fault Fracture Zone

Fault fracture zone is a common geological condition in the process of mountain tunnel construction.When the tunnel passes through the fault fracture zone,the deformation is often too large,which leads to the initial support invading the limit or even cavity collapse in the process of tunnel construction,increasing the risk and construction cost in the process of tunnel construction,Therefore,it is very necessary to study the mechanical response and deformation control standard of the tunnel crossing the fault fracture zone during the construction process,which can provide reference for the subsequent similar projects.Based on the large deformation section of East Tianshan super long highway tunnel crossing fault fracture zone F2,this paper studies the deformation mechanism,deformation law and influencing factors of the initial support of tunnel crossing fault fracture zone by bench method,and on this basis,combined with the field measured data,formulates the stage deformation control standard and corresponding early warning value of the initial support of Tunnel Crossing Fault Fracture Zone V surrounding rock.The main contents of this paper are as follows:(1)Based on the field geological survey and measured data,the deformation and failure characteristics of the initial support of the tunnel crossing the fault fracture zone are analyzed.It is determined that the large deformation section of the East Tianshan super long highway tunnel crossing the fault fracture zone F2 is the large deformation of the squeezed soft rock,and the influencing factors of the large deformation of the squeezed soft rock are analyzed;The squeezing degree of East Tianshan super long highway tunnel passing through F2 fault fracture zone is determined by equal circle method.(2)The numerical simulation and comparison of two bench reserved core soil and three bench method in the large deformation and slight section of tunnel crossing fault fracture zone under different construction parameters are carried out.The deformation of surrounding rock,the range of plastic zone and the maximum and minimum principal stress of initial support of the two construction methods are analyzed,and the optimal construction parameters suitable for the two construction methods crossing fault fracture zone are given.(3)In order to verify the accuracy of the numerical simulation,the displacement and stress of the initial support of the two bench reserved core soil method in the left tunnel of the East Tianshan super long highway crossing the fault fracture zone with large deformation and slight deformation are monitored,and the deformation law of the initial support in each stage of the tunnel construction with the bench method is summarized.(4)Using the method of numerical simulation and on-site monitoring,this paper comprehensively analyzes the effect of double-layer initial support system on surrounding rock deformation in different thickness combinations and different construction time when the tunnel passes through the seriously deformed section of fault fracture zone,and compares and selects the construction parameters of double-layer initial support suitable for the seriously deformed section of surrounding rock in fault fracture zone.(5)Based on the statistical analysis of the surrounding rock deformation of each section of the tunnel passing through the fault fracture zone,the reserved deformation and staged control standard of the tunnel passing through the fault fracture zone are formulated.Combined with the optimization analysis of the secondary lining,a scientific and reasonable early warning value of initial support deformation is proprosed.Part of the research results of this paper have been applied in the East Tianshan super long highway tunnel,and the effect is good,which can provide reference for the control standard of primary support deformation of grade V surrounding rock passing through fault fracture zone.