Disaster Mitigation And Damage Mechanism Of Rock Tunnels With Countermeasures Crossing Active Fault Zones

Active fault zone is an unfavorable engineering geological condition often encountered in the construction of rock tunnels.Meanwhile,the worldwide postearthquake investigations of the recent violent earthquakes revealed that the movement of active faults was closely associated with seismic damage of mountain tunnels intersecting with the active faults,which would be one of the severe challenges in the process of seismic design of tunnels.There have been many cases of countermeasures in practical projects at home and abroad,however,there is still a lack of in-depth and systematic exploration on the disaster mitigation effect and mechanism of countermeasures and relevant design concepts from the basic research level.In this work,the Xianglu mountain tunnel,which is threatened by active faults in the western region of China,is taken as the engineering prototype.Based on the physical experiment method,which makes use of split physical model box to simulate the movement of strike-slip fault,and the three-dimensional numerical analysis method,this dissertation conducts an in-depth and systematic study on the rupture characteristics of rock mass,response characteristics of rock tunnels and disaster mitigation effect and mechanism of countermeasures under different fault rupture mechanisms.The main research work are as follows:1.Experimental study on rock tunnels with flexible articulated joint under strike-slip fault movementThe scaled model of flexible articulated joint system of rock tunnels were designed,and three groups of tests with geometric scale of 1:40 were carried out based on the split physical model box simulating the movement of strike-slip faults.The test results of each group were systematically sorted out and analyzed,and the displacement modes of rock masses and the evolution mechanism of the rupture in the near-surface areas under different stratums were discussed.The results showed that the ductile slip surface regulated most of the fault displacements,and there had an obvious discontinuity between the rock masses on both sides of the slip surface.The failure mode and strain response characteristics of continuous tunnels(without countermeasures)under strikeslip fault movement were selected to compare with the test results of the flexible articulated joint systems carried out in this research.The disaster mitigation of flexible articulated systems on tunnel lining was evaluated.It was found that the collapse of tunnel lining at the sidewall could be avoided and the peak strain response could be significantly decreased by enhancing the overall flexibility of tunnel lining with flexible articulated design.The failure mode and disaster mitigation mechanism of the tunnels with flexible articulated system passing through the fault zone at different angles were revealed,and the deformation and strain response characteristics of the critical sections of tunnel lining were analyzed.The results showed that the tunnel lining segment intersecting the ductile slip surface exhibited the failure mode of the combination of tension and shearing.2.Experimental study on rock tunnels with flexible bellow type joint under strikeslip fault movementThe application and design concepts of bellow steel connection structure were introduced.The structure and design method of bellow type joint were proposed to improve the mechanical properties of flexible joints,and the experimental study of rock tunnels with flexible bellow type joint under strike-slip fault movement was carried out.Comparing the test results of continuous tunnels(without countermeasures)under strike-slip fault movement,it was found that the flexible bellow type joint system could absorb the fault movement through the bending,elongation and shrinkage of bellow connection structure.The bellow type joint played the role of linking between adjacent tunnel lining segments,so that the strain response of tunnel lining was concentrated at the central segment,thereby effectively reducing the damage distribution of tunnel lining and improving the tunnel performance.The failure mode of tunnel structure with bellow type joint was revealed,and the deformation and strain response characteristics of critical sections of tunnel lining were analyzed.It was found that there would be obvious rotational deformation and shear failure in tunnel lining segments,and the cross section of tunnel lining transformed from the circle to the inclined ellipse.3.Numerical simulation on interaction between active faults and rock tunnelsThe remarkable discontinuity and large deformation of fault rupture was simulated using the cohesive interface element.Three-dimensional interaction analysis model between active fault and rock tunnel was established and verified with model test and field observations.Based on the numerical simulation,the deformation and failure characteristics of free-field case under different fault dislocation mechanisms were analyzed.The deformation,strain and damage characteristics of continuous tunnel were investigated,and the effect of fault properties on tunnel lining were revealed.The arrangement of flexible joint,the stiffness of flexible joint,the width of flexible joint and the lining segment length in the flexible joint system were systematically analyzed and investigated.Compared with the numerical results of continuous tunnel,the disaster mitigation of flexible joint system under dislocation mechanisms of strike-slip and dipslip faults were quantitatively evaluated.