Effects of different dosages of PAM and PVA on the physical properties and shear strengths of sandy soil and silty soil

Background To enhance the stability of the soil substrate topsoil layer and solve the problems of disintegration, landslides and soil erosion, it is necessary to clarify the influence of the types and dosages of adhesives on the properties of the substrate. Methods This study used sand and silt as the objects and conducted indoor experiments to explore the effects of polyacrylamide (PAM) and polyvinyl alcohol (PVA) at 0 (control group, CK), 0.2 %, 0.4 %, 0.6 %, 0.8 % (w/w) dosages on soil bulk density, porosity, water-stable aggregates mass fraction and shear strength, and combined with electron microscopy analysis to reveal the soil stabilization mechanism. Results 1. The adhesives significantly reduced soil bulk density (P < 0.05). The reduction in PVA (6.8 % - 10.3 %) was higher than that of PAM (3.4 % - 4.8 %) in sandy soil, and the reduction in PVA (11.7 % - 13.1 %) was also higher than that of PAM (6.2 % - 11.7 %) in silt soil. The effect of PVA was better. 2. The adhesives could significantly increase soil porosity (P < 0.05), and the improvement effect of PVA was more significant than that of PAM, but there was no significant difference among the dosages (P > 0.05). 3. The adhesives significantly increased the mass fraction of large aggregates (P < 0.05), enhanced the stability of soil aggregates, and the effect of PAM dosage was more obvious. 4. The peak value of the principal stress difference of the soil modified by the adhesive increases in accordance with the Mohr-Coulomb law as the confining pressure increases. The strength improvement of sandy soil is better than that of silt soil, and the optimal effect is achieved at a range of 0.4 % to 0.6 %. Moreover, the cohesion of both types of soil increases after modification, but the internal friction angle shows different responses: the cohesion of sandy soil decreases with the increase of the admixture content, while there is no significant improvement in silt soil (P > 0.05).5. The adhesives enhanced the stability of the soil body by aggregating small aggregates, forming thread connections and surface sheet-like structures. Conclusions The adhesives can significantly improve the physical and mechanical properties of the soil substrate, providing theoretical support for improving the stability and erosion resistance of the spray-broadcast substrate, and helping to reduce soil erosion and promote ecological restoration.