Water-induced changes in strength characteristics of polyurethane polymer and polypropylene fiber reinforced sand

As a new kind of air-hardening soil reinforcement material, polymer is being widely applied in river-bank slope reinforcement and ecological slope protection area. Thus, more attention should be paid to study the characteristics of reinforced soil after immersion. In this study, water-induced changes in strength characteristics of sand reinforced with polymer and fibers were reported. Several factors, including polymer content (1%, 2%, 3% and 4% by weight of dry sand), immersion time (6, 12, 24 and 48 h), dry density (1.40, 1.45, 1.50, 1.55 and 1.60 g/cm3,) and fiber content (0.2%, 0.4%, 0.6% and 0.8% by weight of dry sand) which may influence the strength characteristics of reinforced sand after immersion were analyzed. The microstructure of reinforced sand was analyzed with nuclear magnetic resonance (NMR) and scanning electron microscope (SEM). Experimental results indicate that the compressive strength increases with the increase of polymer content and decreases with the increase of immersion time; the softening coefficients decrease with the increase of the polymer content and immersion time and increase with an increment in density and fiber content. Fiber plays an active role in reducing water-induced loss of strength at 0.6% content.