Research on seepage-induced microstructural evolution and hydraulic response in remolded loess: Effects of initial water content and dry density

Seepage-induced structural deterioration exacerbates the erodibility of loess, posing severe geo-ecological risks to engineering projects in the Chinese Loess Plateau. However, the quantitative correlation between the dynamic evolution of water-filled pores and the macroscopic hydro-mechanical response remains elusive. This study systematically investigates the permeability characteristics, structural failure mechanisms, and mechanical behavior of remolded loess under seepage conditions, utilizing nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and isotropically consolidated undrained (ICU) triaxial tests employing the vertical seepage protocol. Results indicate that collapse dominates in low dry density and initial water content samples, where infiltration proceeds through rapid infiltration, collapse hindrance, and stabilization stages. Conversely, cementation dissolution dominates in high dry density samples, characterized by slow infiltration, accelerated dissolution, and stabilization stages. In addition, channel optimization effect dominates in high initial water content samples, and the pore connectivity increases significantly. Seepage increases water content, inducing a transition in the stress-strain response from strain hardening to strain softening, accompanied by progressive reductions in peak shear strength, cohesion, and internal friction angle. By integrating seepage and shear processes, this study elucidates the hydro-mechanical coupling mechanism linking microstructural failure to macroscopic strength deterioration. Furthermore, extreme rainfall and underground pipe leakage can alter pore structures, respectively, triggering collapse under external loads and undermining remolded loess stability. These findings provide a scientific basis for risk mitigation in engineering projects on the Loess Plateau.