Research On Anti-dislocation Technology For Kangyu Tunnel Crossing Active Fault Area On Sichuan-tibet Railway

The development of geological structure in the southwest region of my country,with many active fault zones,and complex surrounding rock conditions have brought new challenges and requirements to the construction of the Sichuan-Tibet line.Under the action of active fault,the tunnel structure that traverses the fault is prone to uneven stress distribution within a certain range around the interface,causing local stress concentration and cracking.It is one of the most difficult problems to study the mechanical response law of the tunnel structure crossing active fault under the action of dislocation and the influence of dislocation on roadway support parameters.Relying on the actual construction of Kangyu Tunnel on the Sichuan-Tibet Line and based on fracture mechanics theory,A three-dimensional finite element model of fault fracture zone in surrounding rock tunnel is established,analyzes related numerical simulation research,and obtains the following main conclusions:(1)Starting from the material characteristics of brittle failure in the tunnel,starting from the ideal situation of a single failure of the tunnel lining,based on the maximum tensile stress theory,it is deduced that the plastic zone at the front of the crack should be a micro-rupture zone.According to the theory of maximum circumferential tensile stress and strain energy density factor theory,the front-end rupture and crack extension and development criteria in the micro-fracture zone under the mode I-II compound crack mode are deduced respectively.(2)Two kinds of formulas for calculating the length of tension staggered joint are derived respectively:(1)Through a general length active fault,based on the ultimate bending curvature of the lining sectionφ_u,the flexible connection of the tunnel—the calculation formula for the length of tensile staggered joints is deduced according to the adjacent flexible connection interval;(2)Traversing an extremely long active fault,according to the width of the fault fracture zone,the inclination of the fault,the thickness of the second tunnel lining,the relative misalignment of the upper and lower walls,the preset width of the anti-fragmentation joints and the tunnel parameters,the quantitative arrangement of the anti-stretching joints along the longitudinal direction of the tunnel is deduced Calculation formula.(3)After analyzing the internal force and deformation response of the secondary lining structure with different fault conditions under different fault conditions,it is found that the fault dip has the greatest effect on the internal force response of the structure;the mechanical response of reverse fault dislocation to the secondary lining structure The impact is second;the fault dislocation is the smallest,which only affects the redistribution of internal forces in the structure.(4)Based on the engineering practice of Kangyu tunnel,a proposed anti-fault structure is proposed.Based on this,a three-dimensional model with anti-fault structure is established,and the force and deformation of the secondary structure under reverse fault dislocation are analyzed.Response law:(1)In the main affected area of the fault,a secondary lining with a segmented hinged structure is adopted,which is manifested as a"segmented"settlement displacement change under the fault action of the fault,which reflects the control effect on the surrounding rock deformation near each lining segment;(2)For tunnels with anti-fault structure,the maximum principal stress response of the dome and invert was reduced by 6.9 times,and the minimum principal stress of the arch waist and arch foot was reduced by 31.2%.The overall evaluation result:the structure may be partially damaged.But the structure as a whole is in the safe working stage.