Stabilization of coarse-grained mixed soils from landslide deposits in Southeastern Tibet using PVA-based composite materials: Mechanical properties and micro-mechanisms

The coarse-grained mixed soils from landslide deposits in southeastern Tibet pose significant risks to infrastructure due to their poor engineering properties, exacerbated by high seismicity and rainfall. This study introduces an environmentally sustainable stabilization method utilizing polyvinyl alcohol (PVA)-based composites as a low-carbon, non-alkaline alternative to conventional cement. The research investigates the synergistic effects of silica fume (SF) and polypropylene (PP) fibers on the shear strength and deformation behavior of these challenging soils. Large-scale direct shear tests were conducted on specimens stabilized with varying dosages of PVA solution (6-14%), SF (2-15%), and PP fibers (0.1-1%) under confining pressures ranging from 100 to 400 kPa, complemented by scanning electron microscopy (SEM) analysis to elucidate underlying micro-mechanisms. Results demonstrate that 10% PVA solution represents the optimal concentration, transforming the soil's stress-strain response from strain-hardening to strain-softening behavior while increasing cohesion to 187.5 kPa. The incorporation of 5-10% SF further amplified peak shear strength by 25-40% through microstructural densification, whereas 0.25-0.5% PP fiber content significantly enhanced ductility, reducing the brittleness index by up to 66% through crack-bridging and anchoring mechanisms. SEM analysis revealed that PVA forms a three-dimensional elastic network encapsulating soil particles, a mechanism optimized by the composite additives. These findings establish a cost-benefit framework for material selection, with optimal formulations identified as 10% PVA combined with 5-10% SF for high-strength applications and 10% PVA with 0.25-0.5% PP fibers for ductile, energy-absorbing applications. The proposed stabilization approach offers potential for enhancing infrastructure resilience in seismically active, ecologically sensitive mountain regions.