Dynamic Response Of Structures On Saturated Ground Based On Fully Coupled Theory

Earthquake induced liquefaction problem is an important but difficult subject in geotechnical dynamic problems. Because of the diversity of influence factors, people still have limit knowledge on earthquake induced liquefaction up to now. Especially, the problem will be more complicated when combined with different engineering structure. In addition, with the increase of city subway and high-speed railway, the enviorment vibration problem due to high frequence moving loads becomes prominent. However, in the current study, the soils are usually treated as single-phase solid medium, not considering the influence of pore water on the dynamic response. In the paper, a fully coupled dynamic FEM program was developed based on the Biot's dynamic consolidation theory. Then the the seismic response of embankment and underground structure in liquefiable sites are investigated, and the environment vibration problem due to the running of metro in saturated stratum is discussed. The main contents of this thesis are described in the following:1. Based on the Biot's dynamic consolidation theory, the dynamic FEM equations are deduced using the finite element method for the solid phase and the finite difference method for the fluid phase. Then a fully coupled dynamic FEM program is developed. In the program, the stress induced anisotropic elastoplasticity constitutive model is implemented. The program is proved to be valid and reliable by comparing the numerical results with the analytical solution and experiment results. An interface routine is developed for the pre-processing, which can convert the model in Hypermesh to the input file for the computation program. 2. Seismic responses of embankment on liquefiable ground are studied using fully coupled dynamic FEM method. The responses such as excess pore water pressure, deformation, and acceleration are analyzed carefully. Special emphasis is given to discuss the influence of water level in reservoir, waterproof measurements, and downstream berm on the response of saturated ground and embankment system. Furthermore, the dynamic response of embarkment subjected to repeated earthquakes is invertigated. The research is referable for a guideline for seismic design of embankment in the future.3. Seismic responses of subway station in liquefiable soil are studied using fully coupled dynamic FEM method. The uplift mechanism is disclosed through the detailed analysis of excess pore water pressure and deformation of saturated soil. Attention is paid to discuss the influence of factors such as thickness of liquefiable soil, initial state parameters of liquefiable soil, modulus of bearing layer, input earthquake wave, groundwater level and reinforcement measurement on the dynamic response of underground structure. The conclusions may offer theory reference for the seismic design of underground structure.4. The environment vibration responses due to the running of subway train in saturated soil are stuied using fully coupled dynamic FEM method. Firstly, the vibration load imposed on the road bed is obtained according to the principles of track dynamics. Then, the vibration propagation rules are obtained through a carefully analysis of responses including acceleration, displacement, and excess pore water pressure. The influences of tunnel buried depth and train speed on the dynamic response are discussed.