Deformation and progressive failure behavior of silty sand stabilized with waterborne polyurethane: A stress-strain-strength perspective

Polymers present a promising avenue for soil stabilization, yet the full deformation process and progressive failure characteristics of polymer-treated soils remain insufficiently understood. This study investigates the strength and deformation mechanisms of silty sand stabilized with a widely used waterborne polyurethane (WPU) through unconfined compression tests. Key aspects evaluated include axial stress–strain response, strength parameters, energy absorption capacity (E₁₀ and E₂₀), failure behavior, and post-failure integrity. The effects of curing time and WPU content were systematically examined, supported by microstructural analyses. Results indicate that WPU forms a cohesive three-dimensional polymer network within the soil matrix, fundamentally enhancing strength and transforming the failure mode to progressive ductile bulging. This polymer architecture enables a high unconfined compressive strength (UCS) of up to 812.39 kPa, substantial deformability with failure strains (ε_f) reaching 12.35%, and notable energy absorption (E₂₀ up to 137.62 kPa). Both strength and toughness increase linearly with curing time and WPU content. An optimal WPU dosage of approximately 3% combined with curing beyond 24 hours is identified to maximize the strength–ductility synergy. Microstructurally, the failure process is delineated into six consecutive stages, governed by the evolution of polymer bridging and interfacial bonding. These findings advance the understanding of the overall deformation–failure behavior of polymer-treated soil and provide deeper insights for the tailored design of polymer-based soil stabilization.