Study on the proportion of double-layer composite base material and vegetation protection performance for rock slope

Aiming at the difficulty of balancing vegetation suitability and erosion resistance with a single base material in the ecological restoration of rock slopes in roadbed engineering, this study proposed a double-layer composite base material composed of vegetation concrete and thick-layer base material. The proportions were designed using an L9(34) orthogonal array. Physicochemical tests and pot vegetation experiments were conducted, and the optimal scheme was selected using analysis of variance, the entropy weight method, and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) method. Simulated rainfall erosion tests were further carried out to evaluate its erosion resistance. The results show that the vegetation concrete had a compact structure and high permeability, while the thick-layer base material was lightweight and porous, with good water retention capacity and a mild chemical environment. The two materials exhibited complementary advantages in structural stability and vegetation suitability. The vegetation performance followed the order of thick-layer base material>double-layer composite base material>vegetation concrete. Compared with single vegetation concrete, the double-layer composite base material showed clear advantages, increasing plant height, vegetation coverage, and total biomass by 72.8%, 51.3%, and 68.9%, respectively. Under rainfall, the erosion resistance of the optimized double-layer composite base material continuously improved with increasing curing age, with the average erosion efficiency decreased by 72.1%. The slope erosion pattern gradually evolved from early-stage sheet erosion to splash erosion and then to a stable slope surface. The findings provide a reference for the design of ecological restoration base materials for rock slopes in roadbed engineering.