Dynamic Analysis Of Poroelastic Foundation And Track System Subjected To High-speed Trains

With the development of high speed railways, dynamic responses of track-ground system and vibration alongside tracks under moving trains are becoming of paramount importance. The excessive vibrations of the track and ground induced by the high speed trains could impact the security of the railway operation, the durability of the structures and the built-up residential and industrial areas. Studies of the dynamic responses subjected to moving trains are important in viewpoints of track stability and environmental protection.First, the dynamic responses of a slab track on the poroelastic half-space subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. It is assumed that the interface of the slab and the poroelastic half-space soil medium is permeable. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground system are solved using the Fourier transform. The dynamic responses in time domain are obtained through the fast Fourier transform (FFT). Effects of the soil intrinsic permeability and the stiffness of slab on soil displacement and acceleration have been carefully analyzed. Numerical results show that the vibration responses of the ground are significantly affected by the fluid phase in the soil medium and soil dynamic responses decrease with increasing stiffness of the slab.Second, the vibrations of vehicle-track-poroelastic ground coupling system subjected to moving train loads are investigated. The theoretical model is divided into three components:The vehicle is described as a multi-rigid-body system and a linear Hertizian contact spring between each wheel and the rail is used to simulate the dynamic wheel-rail interaction forces; a periodically supported Euler beam is introduced to simulate the track system; neglecting the body force and the compressibility of solid grain, Biot's fully poroelastic dynamic theory is applied to formulate the poroelastic half-space. Train loads are divided into two parts:the axle loads and the dynamic wheel-rail loads assumed to be generated from the rail surface roughness. The governing equations of each component are solved using the Fourier transform, and these components of the whole system are integrated to meet the displacement compatibility and force equilibrium by the substructure method. The time domain responses of the ground are obtained through the fast Fourier transform. On the basis of the analysis of the dynamic wheel-rail loads, the dynamic responses of the ground subjected to the axle loads and the dynamic wheel-rail loads are investigated. Influences of the sleeper spacing and the soil intrinsic permeability on the soil dynamic responses are also analyzed.Last, the track system foundation is divided into two parts:the upper layer modeled by transversely isotropic elastic medium and the lower by the poroelastic half-space governed by Biot's theory. The track system is described as a discretely supported Euler beam. The interaction between the sleepers and the transversely isotropic elastic layer is simplified as uniformly distributed vertical loads. Taken car body, bogies, a primary and a secondary suspension into account, the vehicle is modeled as a multi-rigid-body system. A linear Hertizian contact spring between each wheel and the rail is used to simulate the dynamic wheel-rail interaction forces. The governing equations of each component are solved combined with the Fourier transform and the undetermined coefficient method. These components of the whole system are coupled by the substructure method. The dynamic response of the ground is solved in the time domain by applying fast Fourier transform computation. The influence of the train axle loads and the dynamic wheel-rail interaction forces generated from the rail irregularities on the entironmental vibration is carefully analyzed.