Multi-Scale Reinforcement of Shallow Loess Landslides in Frozen Soil Areas using Polyacrylamide-Silica Nanoparticles

Shallow loess landslides in seasonal permafrost zones are typical geological disasters. The alternating freeze-thaw cycles primarily trigger these occurrences. Among the types of soil stabilisers, nanomaterials have small particle sizes and large specific surface areas, which can be well filled in intergranular pores and intragranular micropores. Polymers have the characteristics of environmental friendliness, effectiveness, and low dose. The use of both has attracted increasing attention. To address the conflict between engineering durability and ecological restoration in the prevention and control of shallow loess landslides, this study selected polyacrylamide (PAM) and silica nanoparticles (SiO₂ NPs) as environmentally friendly soil stabilisers. Four different loess mixtures were designed based on different PAM and SiO₂ NP contents: unmodified loess (UL), 3% PAM (PL), 3% SiO₂ NPs (SL), 1.5% PAM, and 1.5% SiO₂ NPs (PSL). This study investigated the effectiveness and mechanisms of the soil stabilisers in preventing and controlling shallow loess landslides through multiple tests, following several freeze-thaw cycles (0, 1, 3, 6, 9, 12, and 15). The tests included slope model, triaxial shear, permeability, and scanning electron microscopy (SEM) tests, combined with vegetation growth control and field in situ experiments. These experiments were conducted in seasonal permafrost regions at multiple scales (macroscopic, mesoscopic, microscopic, and ecological). The results showed that, at the macro scale, three-dimensional laser scanning of the slope model surface indicated that the PSL-treated slope had the optimal surface morphology, the least elevation colour anomalies, and the lowest degree of crack development. As the number of cycles increased, a new colour region appeared in the colour map, indicating the development of additional pores and cracks within the slope. At the meso scale, PSL cohesion increased by approximately 58% to 62 kPa (UL: 18 kPa) after 15 freeze-thaw cycles, and its internal friction angle increased by about 8.9% to 24.23° (UL: 22.23°). The permeability coefficient of PSL (8.03×10^-4 cm/s) was 1.91×10^-4 cm/s lower than that of UL (9.94×10^-4 cm/s). The average rate of change of permeability coefficient of PSL and UL was 1.7% and 1.08%, respectively. At the micro scale, quantitative analysis of SEM images showed that PSL had the smallest pore area ratio and the most stable changes after freeze-thaw cycles. Vegetation experiments confirmed that the solidifier did not affect vegetation growth; rather, it exhibited a promoting effect. Mechanistically, PAM primarily enhanced soil properties through flocculation and water retention, whereas SiO₂ NPs inhibited ice crystal expansion by forming a hydrogen-bond protective layer. PAM and SiO₂ NPs synergistically combined the advantages of both, significantly enhancing freeze-thaw resistance. A 450-day field in situ test further validated that PSL can effectively mitigate freeze-thaw-induced soil degradation, demonstrating excellent application potential for preventing and controlling shallow loess landslides in seasonal permafrost regions.