Mechanical properties and damage evolution mechanisms of polyurethane grouting materials for roadway reinforcement

Chemical grouting reinforcement technology is a crucial method for enhancing the stability of roadway surrounding rock. This study focuses on a novel polyurethane-based composite polymer grouting material, systematically analyzing the mechanical response characteristics, damage evolution laws, and failure modes of grouting bodies with different particle sizes through uniaxial compression tests. Based on the Lemaitre strain equivalence principle, a damage constitutive model for polyurethane grouting bodies was established. Combined with acoustic emission (AE) monitoring and digital image correlation (DIC) technology, the crack propagation mechanisms during the failure process of grouting bodies were revealed. The research results indicate: (1) The peak strength of polyurethane grouting bodies is positively correlated with particle size. Larger particle size specimens exhibit more pronounced brittle characteristics in the post-peak stage, but due to the high ductility and energy absorption properties of polyurethane materials, their residual load-bearing capacity remains at a relatively high level. (2) The established damage constitutive model can accurately characterize the stress-strain relationship and damage evolution process of grouting bodies. The damage curve shows an "upward convex" shape, indicating that the material still retains certain load-bearing capacity in the post-peak stage. (3) The intensity of AE signals increases with particle size, and a significant "dense growth" phenomenon occurs before failure, which can serve as a precursor warning indicator for rock mass instability. (4) Through AE parameters (RA and AF values) and DIC analysis, it was found that internal cracks in grouting bodies are primarily shear failures, with the proportion of tensile cracks decreasing as particle size increases. The failure modes mainly include cohesive failure, grout-rock interface failure, and bonded matrix failure. The research findings provide theoretical support for the optimized design and engineering application of chemical grouting reinforcement technology.