Mechanical characteristics and confinement behavior of geogrid-stabilized railway ballast during tamping operations

Abstract

Ballasted railway tracks exhibit inherently discrete mechanical behavior, and ballast settlement has become increasingly prominent during long-term railway operations. Geogrid reinforcement has shown significant potential in mitigating ballast settlement; however, the mechanical interaction mechanisms between geogrids and heavy tamping machinery remain insufficiently explored. This study established a coupled model based on the Discrete Element Method (DEM) and Multi-Body Dynamics (MBD) to investigate the micromechanical responses and confinement behavior of geogrid-stabilized ballast during tamping operations. Key findings are as follows: (1) During tamping, the geogrid bears its maximum load in the clamping phase, mainly concentrated beneath the sleeper. This phase is identified as the critical stage for geogrid damage, with a 0.41% higher damage increment than the insertion phase. (2) The contact force distribution of ballast across different horizontal planes demonstrates pronounced anisotropy throughout the tamping process. Among these, the upper sleeper-bottom region and the upper inter-sleeper region are the most sensitive to variations in anisotropy. Ballast in the upper layers beneath and between sleepers exhibits peak contact forces at the beginning of the insertion phase, while the bottom layers are less affected. Middle-layer ballast beneath sleepers shows higher sensitivity during the early clamping phase, whereas middle-layer ballast between sleepers is more sensitive from the end of insertion to the beginning of clamping. (3) Geogrid reinforcement effectively reduces the angular velocity and peak contact force of ballast particles during tamping, thereby lowering the risk of ballast breakage due to high-energy impacts. This enhancement contributes to improved tamping quality, as well as better stability and durability of the trackbed. (4) After twelve tamping operations, the geogrid damage ratio reaches 14.06%, yet its restraining effect remains significant, with an average efficiency of 43.3% (56.5% in the first six cycles and about 30% in the latter six), demonstrating robust stability and long-term durability. This research clarifies the mechanical response and confinement behavior of geogrid-stabilized ballast under tamping operations and provides theoretical guidance for improving the long-term performance of ballasted railway tracks.