Discrete element method analysis on mechanical characteristics and response of prefabricated polyurethane solidified ballasted bed

Conventional ballasted beds (CBB) require frequent maintenance, posing significant economic and durability challenges for railway infrastructure. The prefabricated polyurethane solidified ballasted bed (PSBB) has emerged as a promising alternative, offering enhanced stability and reduced unrecoverable deformation. However, the incorporation of polyurethane foaming agents and prefabricated construction methods alters the mechanical properties of the ballasted bed. The influence of polyurethane module size on these properties and the mechanical response of PSBB under train loading remains insufficiently understood. This study develops a discrete element method (DEM)-based numerical model aligned with the PSBB construction process to investigate the effects of polyurethane module size on mechanical performance. Based on support stiffness considerations, an optimal module size is proposed and evaluated under varying train velocities and axle loads. Subsequent to parameter optimization, the model undertakes an evaluation of both macroscopic responses, including accumulated settlement and dynamic stiffness evolution of the track bed, as well as particle-scale behaviour under cyclic train loading. Compared to the CBB, the PSBB demonstrates reduced unrecoverable settlement and slightly lower dynamic stiffness. Increased train velocities and axle weights lead the PSBB to higher accumulated track settlement while insignificant changes in dynamic stiffness. A thorough examination at the particle level has been conducted, yielding noteworthy findings. The analysis has revealed that PSBB exhibits superior load dispersion characteristics in the vicinity of sleeper ends. This property contributes to a reduction in ballast breakage and track settlement. Above insights offer valuable guidance for the design and implementation of the PSBB in railway systems.