Numerical Simulation Of Ground-borne Vibration Due To High-speed Train On Soft Foundation

With the rapid development of high-speed railways and urban rail transit, environmental vibration from trains has become more and more serious, especially when the railway is constructed on the soft foundation, which is unavoidable for the wide range of soft soil in China. Therefore, it’s necessary to do the research on this problem. In this paper, ground vibration caused by high-speed trains is investigatied in which the railway is laid on the soft foundation.The current situation and main aspects of studying on ground vibration is firstly reviewed. Based on the vehicle-track coupling dynamics and finite element method, the numerical model is established which consists of a train-track vertical coupled model and a track-ground finite element model. Using the train-track vertical coupled model, the interaction between train and track is analyzed and the excitation sources are acquired which can be applied on the track-ground finite element model movely or fixedly. After comparison of different force application methods, fixed sleeper forces are selected to arouse the track-ground finite element model.In the case study of soft ground vibration in Sweden, key parameters of the numerical model are further discussed. The soil deformation and vibration characteristics under subcritical and critical train speed are compared. Results show that, both the track irregularity and finite element integral step have great influence on the ground vibration acceleration near the railway. When the train speed is close to the critical value, wave-like deformation will occur and the amplitude of displacement and acceleration will be largely increased. With the increasing distance from track centerline, the vibration energy will gradually decay, in which the high frequency components decay faster.In the research of soft ground vibration from high-speed trains running on the ballastless track, whether considering the elastic soil layer or not in the train-track coupled model is analyzed. Ground vibration at different train speeds and the effect of high embankment on the ground vibration are investigated. Results show that, the elastic soil layer should be considered in the train-track coupled model, so as to simulate the real situation of train running on soft ground. For the homogeneous soil under the action of a single point load, its critical speed is the Rayleigh wave speed. Whereas for the real layered soil, the changing regularity of ground vibration with train speed is not that obvious, owning to the effect of many factors. High embankment may be probably one, which could dampen down the ground vibration level and change the energy distribution of soil surface.At last, the cement soil mixing piles are applied to study the influence of foundation improvement on the vehicle-track vibration and ground vibration. It is shown that, the stability of track structure and embankment will be enhanced and the ground vibration will be controlled after the soft foundation is reinforced.