Static and cyclic compressive mechanical characterization of polyurethane-reinforced ballast in a railway

Polyurethane reinforcement technology can improve the stiffness and the stability of ballast beds. In this study, the performances of the uniaxial compression and fatigue of polyurethane-reinforced ballast with different amplitudes of cyclic loading were studied. The corresponding simulation models were established by the discrete element method (DEM). Then those simulation models were compared and verified with the tests in the laboratory. The mesoscopic mechanical properties of polyurethane-reinforced ballast during compression were analyzed. The uniaxial compression results showed that during the compression process, the stiffness modulus of the samples increased from low to high (increased by 119.93%), and then decreased gradually and gently at the later stage of loading (the stiffness modulus at the turning point was approximately 2.86 MPa) until failure. The mesoscopic results based on the DEM showed that the polyurethane materials not only bore the normal force of the structure but also substantially bore the tangential force. The stiffness modulus of the polyurethane-reinforced ballast decreased with the increase of the loading times but gradually tended to be stable. The cyclic loading results showed that the deformation of the structure did not increase linearly with the increase of the cyclic loading amplitude. The DEM showed that the stiffness modulus of the polyurethane-reinforced ballast was small when the cyclic loading amplitude was large. However, as long as the cyclic loading did not exceed the bearing limit of the structure, the structure could recover to the initial deformation after the cyclic loading was removed.