Abstract:Tailings ponds, as crucial by-products of mining activities, pose substantial geological disaster risks. Particularly in seasonal frozen regions, freeze-thaw cycles induce repeated freezing expansion and thawing contraction of tailings soil, further exacerbating soil structural damage and threatening the safety and stability of tailings ponds. This study investigates the effects of freeze-thaw cycles on the shear strength and key indices (cohesion and internal friction angle) of pure tailings soil and tailings soil amended with plant roots, aiming to provide theoretical support for tailings pond disaster prevention and safety assessment, while exploring the potential of vegetation-based remediation as an eco-friendly stabilization strategy. To explore the influence laws of shear characteristics of pure tailings soil and root-tailings soil under different freeze-thaw cycles, a combination of field sampling and laboratory testing was adopted. Tailings soil used in the experiments was collected from the 0-20 cm surface layer of an abandoned tailings pond in Qianshan District, Anshan City, with surface impurities removed and dried for use to ensure consistency with in-situ properties.?Amorpha fruticosa, the dominant local species, was selected, and its roots were collected from the slope of a tailings dam restoration area. The field density of?Amorpha fruticosa?was approximately 1 m×1 m, with a tree age of 3-5 years, a plant height of 1.8-2.5 m, and a crown width of 1.2-1.8 m. Root-tailings soil composites were prepared by incorporating local plant roots (mainly common herbs in the study area) into tailings soil at a natural root content ratio to simulate real-world root-soil interactions. The effects of 1, 5, and 10 freeze-thaw cycles on the shear characteristics of the root-soil composites were considered. A single freeze-thaw cycle started at 20 °C, cooled to -15 °C over 1.5 h and stabilized for 12 h, then heated to 20 °C over 1 h and stabilized for 12 h, with a total cycle duration of 26.5 h, reflecting typical seasonal temperature fluctuations in the region. After each cycle, direct shear tests were conducted with staged normal stresses (150 kPa, 300 kPa, 450 kPa) and a slow shear rate of 1.2 mm·min?1. The maximum shear force was calculated by recording the shear deformation displacement under each load level, and then the shear strength indices of each sample were obtained. The results indicated that: (1) The shear strength of both pure tailings soil and root-tailings soil decreased significantly with increasing freeze-thaw cycles. Under the same freeze-thaw cycles and loads, the shear strength of root-tailings soil was significantly higher than that of pure tailings soil, demonstrating that root modification can effectively alleviate freeze-thaw deterioration. Under the same conditions, root-tailings soil exhibited notably higher shear strength, as roots enhance the freeze-thaw stability of the soil through physical reinforcement and water regulation. (2) The cohesion of pure tailings soil increased with the number of freeze-thaw cycles, while the internal friction angle decreased substantially, with the internal friction angle dominating the attenuation of shear strength. The cohesion of the root-tailings soil composite showed a trend of first decreasing and then increasing, and the internal friction angle decreased to a smaller extent; roots inhibited strength loss by enhancing soil friction. (3) Freeze-thaw cycles promoted cementation between tailings soil particles, thereby increasing cohesion. However, this enhancement in cementation was insufficient to offset the negative impact of the decreased internal friction angle on shear strength. With the increase in the number of freeze-thaw cycles, freeze-thaw damage inside the tailings soil gradually accumulated, leading to a decline in its overall mechanical properties. These findings provide valuable insights for optimizing geological disaster control measures and improving the safety assessment framework of tailings ponds, thereby helping to reduce risks such as landslides. Comprehensive analysis shows that under the same experimental conditions, root-tailings soil consistently maintained significantly higher shear strength, fully confirming the effectiveness of plant root modification technology in enhancing the freeze-thaw stability of tailings soil. This study not only provides theoretical and technical references for geological disaster control and ecological restoration of tailings ponds but also lays a foundation for improving the safety evaluation system and optimizing engineering practices of tailings ponds in cold regions.

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