Dynamic Interaction Between Track And Subgrade Under Train Load Region With Soft Clay

The subgrade would produce drastic vibration under train load, the phenomenon is specially obvious in soft soil area. Due to the low strength, high compressibility, low permeability of soft soil, the road making engineering technology becomes extremely complex. The settlement after construction and rail operation status were not optimistic since operation condition of rail in built on soft soil foundation comes, and train operation may damage buildings along the rail. In order to decrease the influence of train running on foundation settlement and building damage, accurate analysis of vibration behaviour of the soft soil foundation under train load should be presented firstly, then reliable control methods are proposed. Considered the complexity of rail-subgrade calculation model, the mathematical treatment is quite difficult. The transverse isotropy of soil and influencing factors of rail, sleeper, ballast were negelected in many literatures when the vibration of track system and soil system under a moving train load. Meanwhile, in order to decrease dynamical settlement of foundation under train load, vibration tamping and reinforce by replacing soil are generally used all over the world. But there are some shortcomings, such as: construction cost is high, too much waste soil is difficult to treat. According to the problems aforementioned, the ground vibration due to train load is studied as follows:(1) In order to investigate the dynamic response of rail-subgrade under moving load, a calculation method was put forward in this paper, which is used in solving wave equation of foundation of different types. The thesis first solved wave equation of elastic foundations of isotropic and anisotropy using this calculation method. The analytical solution of ground vertical displacement under moving load is obtained. Then numerical results is obtained using finite element method. The correctness of calculation method is proved by comparing the analytical solution and numerical solution.(2) Based on Biot's dynamic poroelastic theory, the dynamic responses of saturated soils generated by the motion of a train axle load on a railway track in rectangular coordinates was presented by using this calculation method. Apply to boundary conditions of displacement and stress between the two soil layers, the boundary conditions of the surface stress, the solutions for saturated space problem covered an elastic soil layer or an saturated soil layer are obtained. By the train-track-ground model, the paper focuses on the ground vibration along the track, pore pressure and lateral earth pressure generated by the train on the layered saturated soil. The influences of train speed , track stiffness and permeability coefficient on ground vibration, pore pressure and lateral earth pressure are analyzed.(3) For soils are deposited through a process of sedimentation over a long period of time, anisotropy soils are often modeled as transversely isotropic saturated poroelastic media. The constitutive relation of anisotropy was substituted in Biot wave equation, then the transversely isotropic saturated soil dynamic equation was obtained. The influence of anisotropy parameter on ground vibration, pore pressure and lateral earth pressure are analyzed by solving the dynamic equation.(4) According to the analysis of chapters above, we find that high strength elastic layer had a remarkable effect on decrease subgrade settlement of soft clay foundations. So the light soil is used in settlement control of rail-subgrade system in soft soil area in this paper. The property of new geotechnical material—light soil, which is prepared using soft soil was analyzed by experiment. Meanwhile, a series of laboratory tests are carried out to study the anisotropy of soft clay and the constitutive parameter of anisotropy are obtained. The application effect is analyzed by finite element software.