Research On The Dynamics Characteristic And Longtime Subsidence Of The Railway Tunnel's Base In Xigeda Strata Based On Continuum-discrete Coupling Method

With the further development of the western region of China, The construction of the railway in Southwest China has a new climax. The new Chengdu-Kunming Railway is under construction and it will across the Xigeda strata that are unique in the west of Sichuan. Xigeda strata is a type of river and lake sedimentary rocks and it is a soft, easily weathered strata,which is likely to become soil and silt by hand pinch and has a characteristic of easily softening and disintegrating in contact with the water. According to tunnel disease research of existing Chengdu-Kunming Railway, Every tunnel in Xigeda strata has experienced a large number of diseases, especial in mud pumping under base, roadbed subsidence, lining cracking, bringing a great security risk to the old Chengdu-Kunming railway operation.Granted from the program of National Science Foundation of China 'Study on the Carrying Capacity of the Surrounding Rock of the High-speed Railway Tunnel and its Catastrophe Control Technology in Xigeda Formation Stratum ', This dissertation studied the dynamics characteristic and the damage of the base of the tunnels in Xigeda strata induced by train load and proposed long-term subsidence formula of the basement of Xigeda tunnel. Using a variety of research methods, such as literature research, theoretical analysis, indoor triaxial test, numerical simulation of discrete-continuous coupling method, this dissertation aimed to provide a scientific basis for the construction of the base of Xigeda tunnel, to improve construction technology, to reduce various kinds of diseases caused by train load in the later period of operation and to save a large number of late maintenance costs. The main research work and conclusions are as follows:(1) Dynamic triaxial tests were conducted under different conditions, including different dynamic stress, static deviator stress, confining pressure, consolidation ratio and load frequency,to study the law of cumulative plastic deformation, dynamic modulus and damping ratio of Xigeda clay under cyclic loading and to establish a cumulative plastic deformation model considering the moisture content. Experiments show that the cumulative plastic deformation curve of the Xigada clay can be divided into stable and destructive and the curve type is mainly affected by the dynamic stress ratio and the moisture content. The cumulative plastic deformation increases with the increase of dynamic stress ratio, static deviation stress ratio and water content, and decreases with the increase of confining pressure and load frequency.(2) The continuity of the stress of the FLAC3D coupling algorithm at the coupling interface is verified by the simulation of punch impact tests. Based on the indoor triaxial shear test data, the triaxial test model was established in FLAC3D and PFC3D respectively, and the microscopic and macroscopic parameters of Xigeda clay were calibrated.(3) The dynamic characteristics of the Xigada tunnel under the train load are analyzed by discrete - continuous coupling method. The method is that the vicinity of the bottom of the invert is simulated by discrete element, and the other regions are simulated by continuous medium. The results show that the acceleration of the train can be divided into the initial acceleration and the stable acceleration. As the train speed increases, the initial acceleration peak increases slowly, the steble acceleration increases significantly, and the peak value of the dynamic stress increases.