Evaluating the Impact of Mudstone Swelling on Railway Heave of Ballastless Tracks in the Transition Section Using the DEM-FDM Coupling Method

Mudstone is widely distributed in various regions of northwest China. Due to its high susceptibility to swelling when exposed to water, constructing high-speed railways in shale-prone areas often leads to track heave issues. Among these, the culvert transition section is a high-risk segment for the occurrence of such track deformations. This study employed a coupled numerical simulation method integrating the discrete-element method (DEM) and finite difference method (FDM) to model and analyze this problem. Swelling soil tests were conducted using a self-developed soil expansion testing apparatus. The study analyzed the deformation patterns of double-block ballastless track rails induced by foundation swelling in the transition section of a culvert. It investigated the movement trend of the subgrade fillers and the heave response of the rails when the foundation soil near the culvert is subject to varying swelling rates, with the distance between the swelling zone and the culvert being 0 (Case 1), 5 (Case 2), and 10 m (Case 3). The numerical simulation results indicate that the culvert restricts the transmission of rail displacement, resulting in a relatively small displacement at the top of the culvert but causing larger displacements on both sides of the culvert. If foundation swelling occurs in the transition section, the active earth pressure on the culvert's side wall increases due to the extrusion of the fillers, and the culvert body tilts. When a portion of the swelling zone is located below the culvert while another part is situated behind the culvert, the resulting deformation response of the railway track and the maximum stress concentration are observed.