Moisture Change of Modified Soil and Spatial–Temporal Evolution of Vegetation Cover for Bio-Slope Engineering in a Plateau Railway

Bio-slope engineering protection plays an important role in preventing soil erosion, enhancing slope stability, and improving soil and water conservation capabilities. To establish a foundation for the preparation of modified soil for bio-slope engineering, the common gravel soil used in bio-slope engineering protection was selected. Amendments such as peat soil and water-retaining agents were then incorporated to support these preparations. This study examines the influence of the content of peat soil and water-retaining agent on the modified soil’s moisture constants, infiltration coefficient, and water absorption capacity. Additionally, utilizing remote sensing technology, 20 rock cutting sites sprayed with vegetation were monitored over a 15-year period. The results suggest that the addition of peat soil and water-retaining agents aids in augmenting the available water capacity and water absorption speed of the soil, allowing it to absorb and retain a substantial amount of available water capacity. However, as the content of peat soil increases, the modified soil’s wilting point improves, while the infiltration coefficient increases. Based on the findings of the optimum proportion tests and the field spraying experiments, it is recommended that the proportion is granular soil with 80%, peat with 20%, water-retaining agent with 1.0‰, aggregate agent with 1.0‰, and fertilizer with 100 g/m2. A comprehensive analysis of the spatial–temporal evolution characteristics of vegetation cover in the area post-railway construction indicates that vegetation cover in this region wilted extensively only in 2011 due to drought. Subsequently, the vegetation on the sprayed rock slopes has thrived, according to the proportion. The research findings are of considerable importance for guiding the design and construction of substrate spraying for bio-slope engineering protection in railway construction.