Vegetation concrete is one of the most widely used substrates in ecological slope protection, but its practical application often limits the growth and nutrient uptake of plant roots due to consolidation problems, which affects the effectiveness of slope protection. This paper proposed the use of a plant protein foaming agent as a porous modifier to create a porous, lightweight treatment for vegetation concrete. Physical performance tests, direct shear tests, plant growth tests, and scanning electron microscopy experiments were conducted to compare and analyze the physical, mechanical, microscopic characteristics, and phyto-capabilities of differently treated vegetation concrete. The results showed that the higher the foam content, the more significant the porous and lightweight properties of the vegetation concrete. When the foam volume was 50%, the porosity increased by 106.05% compared to the untreated sample, while the volume weight decreased by 20.53%. The shear strength, cohesion, and internal friction angle of vegetation concrete all showed a decreasing trend with increasing foaming agent content. Festuca arundinacea grew best under the 30% foaming agent treatment, with germinative energy, germinative percentage, plant height, root length, and underground biomass increasing by 6.31%, 13.22%, 8.57%, 18.71%, and 34.62%, respectively, compared to the untreated sample. The scanning electron microscope observation showed that the pore structure of vegetation concrete was optimized after foam incorporation. Adding plant protein foaming agents to modify the pore structure of vegetation concrete is appropriate, with an optimal foam volume ratio of 20-30%. This study provides new insights and references for slope ecological restoration engineering.

Traditional slope protection methods face many challenges when applied to carbonaceous mudstone slopes. The objective of this study was to develop a novel protection method based on vegetation concrete with carbonaceous mudstone aggregates (VCCMA) and then examine its performance and underlying protective mechanism. Hence, physical model tests were performed on highly-weathered carbonaceous mudstone slopes under wet-dry cycles considering three different protection cases, i.e., no protection, protection using porous concrete with carbonaceous mudstone aggregates (PCCMA) and protection using VCCMA. The erosion characteristics, volumetric moisture contents, and slope deformations of the slopes were measured. Finally, the performances and underlying mechanisms of the protection methods for slopes were compared. The results demonstrate that the unprotected slope, the PCCMA-protected slope, and the VCCMA-protected slope were descending according to the erosion damage, the particle loss amount, and the deformation during five wet-dry cycles. Among the two protected cases, the VCCMA exhibits better erosion coefficient, water retention capacity and disintegration resistance of the slope. The runoff volume depends on the protection method and shows a weaker correlation with wet-dry cycles. In the case of PCCMA protection, the protection effects come from self-weight consolidation, water interception, and integral protection structure. The VCCMA protection case incorporates additional protective mechanisms, including soil moisture regulation by leaf transpiration, resistance to rainfall splashing and scouring by stems and leaves, and soil reinforcement and anchoring by roots. Therefore, the VCCMA holds significant potential for effectively protecting problematic slopes. These findings provide valuable guidance for the protection of highly-weathered carbonaceous mudstone slopes.