Research on soil improvement and engineering application under mixed application of environmental materials in alpine mining areas

To address the issues of inadequate topsoil structure, soil erosion, and low soil fertility in the reclamation of alpine mining areas. Taking Qinghai West Copper Mine as an example, this study investigates the impact of three materials—sheep manure(A), TG modifier(B), and water retaining agent(C)—on soil improvement using a simulated orthogonal design experiment. The experiment aims to identify the optimal mixing ratio that yields the most significant improvement. Orthogonal polar results revealed that sheep manure had a more pronounced effect on soil organic matter, soil bulk density, porosity, and total salt content. Meanwhile, TG modifier demonstrated a stronger impact on pH, and the water retaining agent exhibited a greater influence on water-holding capacity in the field. The combined results of extreme difference analysis and principal component analysis indicated that treatment 1(A 6 g/kg, B 1.85 g/kg, C 0.06 g/kg) represented the optimal combination of physicochemical properties for soil improvement. Redundancy analyses yielded that sheep manure and TG modifier explained the best variability in soil physicochemical properties. Organic matter, soil field water holding capacity, and porosity exhibited significant correlations with environmental materials. Organic matter displayed a positive correlation with sheep manure, while porosity and field water holding capacity were positively associated with water retaining agent and TG modifier. Conversely, pH, total salt content, and soil bulk density demonstrated weaker correlations with environmental materials. Porosity and field water holding capacity were strongly positively correlated and both were negatively correlated with organic matter. Considering the optimal combination of soil organic matter (A3B3C2) and other soil physicochemical properties (A1B1C1), the optimal formula for soil matrix restoration in alpine mining areas was determined using the median algorithm as A2B2C1.5. This corresponds to 12 g/kg of A (sheep manure), 3.7 g/kg of B (TG modifier), and 0.09 g/kg of C (water retaining agent) as the optimal ratios. The engineering application process, primarily centered around activities such as slope trimming, hanging coconut/barbed wire, hanging ecological rods, setting up drainage ditches, screening of guest soil, spraying of alien soil, laying of water-preserving blankets, and maintenance management and monitoring, was summarized. This summary integrates research on experimental formulations with practical engineering applications. The results of the engineering applications of the three environmental materials illustrate that soil physicochemical properties and biomass were also significantly improved. This study provides a reference to address the restoration of soil fertility and structure in high-altitude mining areas of Qinghai-Tibet, which is of great significance for soil and water conservation.