Dynamic Properties Of Soft Rock And The Safety Of Base Structure Of High-speed Railway Tunnels

With the rapid development of high-speed railway construction in China, more and more high-speed railway tunnels which cross through soft ground are currently being built. In order to meet the high standards of high-speed trains running in the tunnel, more and more requirements were set for the dynamic stability of the bottom bedrock and the safety of the lining structure of the tunnel. Therefore, the dynamics of the high-speed railway tunnel structure have become increasingly prominent.According to the dynamical problems of the high-speed railway tunnel in soft rock conditions, the dynamic response, damage characteristics and the process of dynamic strain and the law of cumulative plastic deformation of the base soft rock are investigated by using methods as theoretical analysis, laboratory test and numerical calculation. The influence of the bed situation on the force status and the long-term performance of railway tunnel lining structure are further studied in this dissertation. The dissertation is granted from the Major State Basic Research Development Program of China(NO:2011CB013802), the National Natural Science Foundation of China(NO:50808176), and the Science and Technology Development Plan Project of the Ministry of Railways. The main research contents and conclusions are as follows:(1) Based on the elastoplastic damage theory, the damage equations of concrete and soft rock are established, and the damage evolution equations are derived respectively. By introducing the damage variables into the hyperbolic Drucker-Prager criteria, the elastoplastic damage models are constructed which can be taken into account the stiffness and strength degradation of concrete and soft rock. The constitutive integration algorithm of the damage models is derived, and the program development of the models is completed by using the UMAT subroutine in ABQUS finite element software. Comparing with the results of previous tests, effectiveness of the proposed models is verified. (2) A soft rock cyclic triaxial testing system is developed which can be considered the impact of confining pressure and groundwater seepage, the dynamic deformation tests of soft rock with the influence of dynamic stress, static deviator stress, vibration frequency, confining pressure and groundwater are carried out by using this system. The laws of dynamic strain of water-rich soft rock and the influence degree of various factors on the accumulative deformation are obtained, and the accumulated plastic strain prediction model has been established. The cumulative deformation law of the composite member with soft rock and concrete is studied by the dynamic tests under different combination state.The test results show that the irreversible deformation of soft rock increases with the increasing of dynamic stress, static deviator stress and confining pressure, reduces with the increasing the vibration frequency. It is affected significantly with the changing of the underground water condition and the bed situation.(3) Dynamic responses and damage characteristics of bedrock are analyzed systemically in different conditions, such as the train running speed, the types of tunnel base structure and so on.The results show that the influence depth caused by train vibration in tunnel is about5m below the basement. Compared dynamic stress response with acceleration response, the changes of train speed has most influence on bedrock acceleration, and the changes of invert arch thickness on dynamic stress. Changing the invert arch rise-span ratio is more efficiency than increasing the thickness of invert arch in the way of reducing vibration effect.(4) Taking the high-speed railway tunnel in V class surrounding rock in water-abundant ground as the research object, the long-term cumulative deformation behavior of the tunnel in soft bedrock is analyzed with the cumulative plastic strain prediction model.It can be concluded that the cumulative deformation of tunnel foundation has been increased with the increasing of train speed, the decreasing of invert arch rise-span ratio and thickness. It is affected significantly when the bedrock softening. The calculation results also indicate that long-term settlement of tunnel in soft bedrock is enough to meet the requirements of the smoothness of ballastless track.(5) The influence of the bed situation on the force status of railway tunnel structure is studied by using dynamic numerical method. Meanwhile, based on the damage cumulative theory, a power-type equation of the non-linear damage cumulative criteria is proposed to predict the fatigue life of high-speed railway tunnel structures in different condition. The influence of the bed situation on the long-term performance and development trends of the tunnel structure is further analyzed. And then, some effective measures are put forward to improve the life of tunnel.