Study On Dynamic Response And Failure Mechanism Of The Crossing-fault Tunnel Under The Action Of Active Fault

The stress and deformation characteristics of tunnel structure through the active fault is extremely complicated under the action of strong earthquakes.Once the active fault is dislocated,it will have a significant impact on the safety of the tunnel structure.In this dissertation,we study the theoretical displacement field caused by fault displacement from the displacement theorem,and educed the slip velocity function,then expand the numerical simulation to study the form of fault and the slip speed and other issues.With the application of the slip velocity function,the actual engineering condition of the tunnel structure through the active fault under the action of strong earthquakes is simulated,and the mechanism of the stress and deformation is studied and compared with the actual earthquake damage.At the same time,the effect of shock control measures is studied for such engineering problems.The main results and conclusions of this paper are as follows:(1)Based on the displacement theorem,the theoretical displacement field caused by the fault in the uniform elastic full space is studied,and the formula of the displacement field of the rectangular finite fault is obtained.Theoretical formula shows that the effect on displacement field caused by slip velocity cannot be ignored.(2)Through the numerical simulation of cross-fault tunnel,the effects on surrounding rock and tunnel structure of three kinds of faults are simulated,and it isfound that the normal fault is the most unfavorable to the tunnel structure.Meanwhile,the fault slip velocity is studied,the study indicates that the greater the fault slip velocity is,the greater the corresponding increase of principal stress is,the lower the structural safety factor is,and the stress concentration at the fault and nearby location is obvious.By comparing the slip velocity function,it can be concluded that the smoothness of the velocity change has some influence on the structural principal stress and safety.(3)By analyzing the stress and deformation characteristics of the tunnel crossing active fault under strong earthquake,it is found that the deformation of the tunnel structure is mainly controlled by the dislocation at the fault or nearby location.The deformation of the tunnel structure is mainly caused by the horizontal ground motion.The internal force of the structure is consistent with the deformation,and the rate of displacement is influential.The magnitude of the deformation or internal force fluctuation caused by ground motion is enlarged in the vicinity of the fault.(4)Compared with the actual damage of Longxi tunnel in Wenchuan earthquake,it is found that the damage is particularly significant on both sides of the fault zone.Local collapse occurred in the vault and arch,and there are serious earthquake damage such as uplift and cracking at the invert,and the oblique crack is mainly developed in the reinforced concrete of the arch foot and the nearby position,which is mainly shear cracks.The above results are consistent with the analysis results of the structural deformation and internal force.(5)The damping effect of the flexible joint,the damping layer and the composite damping measures are studied.The results show that because of the flexible joint,the damping layer and the composite damping measures,the maximum reduction of the structural principal stress respectively is about 30%,50%and 55%.The composite damping measures have the best damping effect.It is found that the flexible joint has obvious control effect on the fault influence range,and it is suggested to be used in the cross active fault tunnel engineering,and combine with multi-stage damping structure to ensure the safety of tunnel.