The Mechanical Properties of Polyurethane-Solidified Ballast with and Without Geogrid Reinforcement

Polyurethane-solidified ballast (PSB) technology and geogrid reinforcement can be used to strengthen ballast beds. However, there has been little research on the mechanical properties of ballast beds under the combined effects of these two methods. This study addresses this research gap through an integrated experimental–numerical investigation of the cooperative reinforcement mechanisms. Uniaxial compression and oblique shear tests were conducted on standard and geogrid-reinforced PSB specimens, and a three-dimensional random aggregate finite element model was developed to represent the actual ballast gradation. The results show that geogrid reinforcement increased the compressive strength by 42.1% and reduced the maximum lateral deformation by 14.2%, while having little influence on the elastic modulus and Poisson’s ratio. In the oblique shear tests, geogrid reinforcement increased the peak loads by 14.2–23.0% compared with the standard specimen. A directional dependence was also observed, with the highest peak load occurring when the shear plane corresponded to the unreinforced surface. These findings clarify the cooperative reinforcement mechanism between polyurethane solidification and geogrid confinement and provide a mechanical basis for designing reinforced ballasted trackbeds in heavy-haul railways subjected to high axle loads and pronounced lateral deformation, as well as in high-speed railway lines requiring enhanced track stability.