Study On Damage And Fracture Mechanism And Anti-Displacement Performance Of Metro Tunnels Passing Through Active Faults

Taking ‘the Belt and Road’ as an opportunity,the tunnel construction in the central and western regions of China is in full swing.Xinjiang,Tibet,Gansu,Ningxia and other provinces began to plan or have been building multiple mountain tunnels,subway lines,oil and gas pipelines,etc.The construction of subways in the central and western cities will become an important force for the country to lead strategic investment,drive economic development,and improve people’s lives.The subway tunnel project which passes through complex geological structure areas such as active faults has become a normalized and difficult point project,and the scientific design,safety construction,disaster prevention and mitigation of related tunnel projects have become the focus of the tunnel engineering community.In recent years,active faults have caused more and more damage to the tunnels.Large displacements under the action of active faults will cause complex three-dimensional deformation to the subway tunnel,leading to serious damage,distortion and distortion.At home and abroad,however,there are no mature fortification systems and related specifications to be followed.There are many unclear scientific problems in this field,and `a lot of technical challenges that have never been encountered before.Therefore,it is of great scientific significance and engineering value to study and discuss the structure of subway tunnel under active fault to study its stress characteristics,failure mode and fortification principle which provides technical reserves and support for the design and construction of the active fault subway tunnel at this stage.Based on the National Natural Science Foundation of China,“Study on the Catastrophic Behavior of Subway Tunnels and Supporting Structures of Support Structures under Active Faults and Sticks”(Project Approval Number: 51478396)and the Xinjiang Urumqi Autonomous Region Science and Technology Plan Project “Study on Key Technical Issues of Metro Tunnel Structure Engineering in Active Fault Zone”(Project Approval Number: 2015-08),theoretical analysis,engineering analogy,numerical analysis and laboratory test are combined in this paper to systematically study the forced response law,failure mode and fortification system of the lining structure of the subway tunnel passing through the active fault.The main results and conclusions of the thesis are as follows:(1)Based on the influence of buried depth,stratum property,fault dip and strike,displacement mode,tunnel fault angle and fault distance,a three-dimensional double-contact forced displacement model of “fault-tunnel” is established.Considering the key characteristics of the longitudinal displacement characteristics of the tunnel structure,the range of the void area,the distribution characteristics of the fractures,and the safety factor of the section,the safety evaluation method of the tunnel lining structure under the condition of active faults is proposed.(2)Under comprehensive consideration of key parameters such as longitudinal displacement characteristics of the tunnel structure,the extent of the void area,the distribution of cracks,and the safety factor of the section,the degree of longitudinal damage and the extent of damage of the tunnel structure are defined hierarchically.The concept of vertical defense zone of the tunnel structure(main control zone and affected zone)is proposed.And for the first time in China,the quantitative criterion for the length of the longitudinal division of the tunnel is set up under the condition of active fault-slip sliding(3)By introducing a Cohesive Zone Model based on damage fracture mechanics,the numerical simulation of the classical fracture test of concrete materials is carried out to realize the calibration of the parameters of type I(expanded type)and type II(in-plane shear type)of CZM model.(4)This paper uses Matlab and Python programming methods to achieve batch modeling of cohesive elements.The traditional integral tunnel finite element model based on CZM is established as well as the cracking process of tunnel crack type I and type II under the condition of active fault fault-slip.The traditional integrated tunnel failure mode is also clarified,and the damage degree and damage extent of tunnel structure are quantified.(5)Based on the concrete damage plasticity CDP(Concrete Damage Plasticity)constitutive model,the finite element model of the articulated segmental tunnel structure passing through the active fault is established,and the damage evolution process and damage distribution feature of the tunnel structure during the stick-slip dislocation of the active fault are revealed.The anti-dislocation mechanism of reinforcement measures such as enhanced reinforcement,lining segmentation and flexible joints is proved,and the anti-misplacement performance of the articulated segmented tunnel structure is comprehensively analyzed to provide scientific guide for design optimization and fortification measures for the structure of the active fault tunnel.(6)This paper adopts the self-developed large-scale,multi-inclined,high-precision crossfault fault subway tunnel structure simulation loading test device to carry out the model similarity test of traditional monolithic tunnel and articulated segmental tunnel.Considering the expansion of section size,reinforcement of structural reinforcement,lining section and flexible joints,the forced deformation range,damage degree and failure mode of tunnel structure fortification system under fault displacement conditions are revealed.Establish a tunnel structure fortification system guided by the principle of “partition fortification,couple hardness with softness”.(7)Based on the spectral characteristics of the active faults associated with active faults,considering the pulse characteristics of near-fault seismic waves,the structure of the tunnel structure is determined by the combination of ground motion and fault displacement.The load sharing ratio of fault displacement and ground motion respectively subjected to the structure is explored,and the main cause of the structural damage of the tunnel and the damage process are explored.