Analysis on the Dynamic Stress Characteristics of the Unballsted Track Subgrade under Train Loading
Taking data measured on site as the basis and combining with theoretical analysis and finite element calculation,referring to the situation when loads of a running train were transmitted from unballasted tracks to subgrade surface,the distribution pattern and frequency response characteristics of dynamic stresses and the attenuation law of dynamic stresses along the subgrade depth were investigated.The following conclusions are drawn:(1)Because unballasted tracks possess good load diffusion effect,one loading and unloading cycle of dynamic stresses on subgrade surface is completed by co action of two axle loading of one bogie,and it is simplified into distribution of trapezoids in the longitudinal direction and uniform distribution in the lateral direction;(2)dynamic stresses attenuate slowly along the subgrade depth under two axle loading,and their attenuation rate is decreased to 50% at the bottom of foundation,about 10% more than the measured value;(3)the frequencies of dynamic stresses acting on subgrade surface are excited by train loads and are mainly controlled by vehicle lengths and bogie intervals,the frequency response characteristics corresponding to the bogie pitch are gone,and the maximum acting frequency is 4 times the fundamental frequency generated by the vehicle length.