Analysis of Ballast Breakage in Ballast Bed when Using under Sleeper Pads

A breakable model of ballast particle is developed by using the Discrete Element Method (DEM). A method of modelling the Under Sleeper Pad (USP) by using 'elastic rods' is proposed. After integrating the model of the sleeper, USP and ballast, the dynamic train load is applied to analyze the dynamic response of the ballast bed. The following results can be drawn: (1) The USP increases the contact area between the sleeper and ballast particles, and effectively reduces the contact stress. Comparing the track using USP to the traditional ballast track, maximum stress in ballast is reduced by 26.10%, and the average stress is reduced by 3.22%. (2) The breakage of ballast particles in the upper part the ballast bed of the traditional ballast track is mostly overall damage, while the breakage in the lower part mainly occurs at the sharp corners. Using the USP can mitigate the overall breakage at the upper part. (3) The USP can reduce both the tensile failure and shear failure of ballast breakage compared to the traditional ballast track. (4) When using the USP, the ballast settlement is faster to be stable and with a smaller value under long-term train loads.