Polymer-fiber combined effect for improving sand mechanical and micro-damage response

Sand instability is always an intractable problem in geotechnical engineering and its reinforcement using additives is an effective method. This paper introduces the organic polymer reinforcer (OPR) and the recycled polypropylene fiber (RPF) to modify sand. The unconfined compression and corresponding numerical tests were performed to investigate mechanical properties, deformation failure behavior, and microscopic response. Results showed that both materials positively affect the mechanical and deformation properties of modified sand synergistically. Optimized particle structure by the inter-particle polymer membrane linked the loose sand into a whole with fibers as a framework. Strain-softening properties were reduced with less strain localization under loading. This is also clearly related to the improvement of the micro-damage based on numerical results. OPR-RPF reinforcement transformed the bond failure from unidirectional concentration to multilocal dispersion by improving force chain construction, microcrack propagation, and energy allocation. Thus, the failure of modified sand showed a macroscopic progression from shear-faulting via ductile-faulting to ductile flow. Future research lies in further considering the particle shape and pore structure variations to provide new insights for a deeper understanding of sand stabilization mechanisms and engineering applications.