Dynamic Responses Of Poroelastic Soil And Traffic Line System Under High Speed Traffic Load

Studies of the dynamic response of railway track and adjoining ground under the action of moving train has received considerable attention in a number of engineering fields such as civil engineering, transportation engineering and environmental engineering. Recently high-speed trains are becoming increasingly popular and freight trains becoming heavier. Combined with this finding and the observation that Rayleigh wave speeds are slow in soft soils, it can be seen that the study of the dynamic response subjected to moving train load is important for environmental sense of the along side built-in area.The dynamic response of a transversely isotropic poroelastic half-space soil medium and soil medium under elastic beam on rigid rock subjected to moving loads are studied analytically/ numerically under conditions of plane strain. The full dynamic poroelastic theory of Biot is employed, under the assumption of an incompressible solid grain and neglecting the apparent mass density. The loading function is presented by a Fourier series expansion. By using the boundary condition at the surface of the soil, the governing equations of motion are then solved. The effect of transversely isotropic on soil vertical displacement is discussed under different parameters such as load speed and coefficient of permeability. Numerical results of vertical displacements are given and indicate that transversely isotropic have much effect on the response of the soil. While investigating the dynamic response of soil medium under elastic beam on rigid rock, the effect of the beam is considered by jointing the governing equation of the beam with the boundary condition of the soil medium. The effect of the rigidity of the beam on soil vertical displacement and pore pressure is studied particularly.The three dimensional steady state responses of a poroelastic half-space soil medium subjected to a moving rectangular load are investigated analytically/numerically. The full dynamic poroelastic theory of Biot is employed, under the assumption of an incompressible solid grain and neglecting the apparent mass density. Using the triple Fourier transform, the governing equations of motion are then reduced to a system of four coupled ordinary differential equations which are solved semi-analytically. Soil vertical displacements, accelerations and pore water pressures induced by moving load are calculated. Computed result shows that load velocity and intrinsic permeability of the soil medium shows an apparent effect on its dynamic responses and pore water pressures.Further more the three dimensional steady state responses of pavement systems subjected to a moving traffic load are investigated. The traffic loads are simulated by four rectangular load pressures, and the rigid and flexible pavement systems are regarded as an infinite plate resting on a poroelastic half-space soil medium. The contact surface between the plate and the poroelastic half-space is assumed to be smooth and fully permeable. Kirchhoff small-deflection thin-plate theory is employed to analyze the plate; while Biot's fully dynamic poroelastic theory is used to characterize the poroelastic half-space. The frequency wave number domain solution of the pavement system is obtained by the compatibility condition between the plate and the poroelastic half-space. By applying the inverse fast Fourier transform, the time domain solution is obtained. Also, the influences of the load speed, the permeability of the soil, and the flexural rigidity of the plate on the response of the pavement system are investigated. The numerical results show that the influences of these parameters on the dynamic response of the pavement system are significant.Based on solution of the Biot's theory given in the former part, the dynamic responses of a track system and poroelastic half-space soil medium subjected to moving point load and train passages are investigated by the substructure method. The whole system is divided into two separately formulated substructures, the track and the ground, and the rail is described by introducing the Green function for an infinitely long Euler beam subjected to the action of moving axle loads of the train and the reactions of the sleeper. Sleepers are represented by a continuous mass and the effect of the ballast is considered by introducing the Cosserat model for granular medium. Using the triple Fourier transform, the governing equations of motion are then solved analytically in the frequency-wave-number domain. The time domain responses are evaluated by the inverse Fourier transform computation for a certain train speed. Computed results show that the shape of the rail displacements of the elastic and poroelastic soil medium are in good agreement with each other of the low train velocity, but the result of the poroelastic soil medium is significantly different to that of the elastic soil medium for the high train velocity which is higher than Rayleigh-wave speed in the soil. The influence of the soil intrinsic permeability on soil responses is discussed with great care in both time domain and frequency domain. The dynamic responses of the soil medium are considerably affected by the fluid phase as well as the load velocity.Practically, due to the ground water table being of several meters beneath the ground surface, the soil profile can be divided into two layers: the upper layer modeled by elastic medium and the lower layer by fully saturated poroelastic medium governed by Biot's theory. In this part, the former rail track model and train model is introduced. The influences of the thickness, the mass and the rigidity of the elastic layer and the mass of the ballast on rail's displacement responses are carefully investigated. Numerical results show that the influences of these parameters are significant for high train velocity, while vanishes for low velocity.Finally, the vibration of a vehicle-rail-ground coupled system is studied semi-analytically. The theoretical model incorporates vehicles, a track and a saturated poroelastic half-space soil medium, and a Hertizian contact spring is introduced between each wheelset and the rails to consider the dynamic forces. The source of vibration excitation is divided into two components: the moving axle loads and the dynamic loads caused by the vertical rail irregularities. Biot's fully dynamic poroelastic theory is used to characterize the poroelastic half-space soil medium, and the rail is modeled by infinite Euler-Bernoulli beam. The governing equations for the vehicle, the track and poroelastic soil are solved by Fourier transform. The effect of the vehicle-rail couple and the rail irregularity is studied.