Increasing the water–cement ratio and water-reducer dosage of cement slurry enhances its fluidity. However, a high water–cement ratio diminishes the beneficial effects of water reducers on fluidity. The stone content of the slurry decreases as the water-reducer dosage increases. Additionally, the water–cement ratio significantly affects stone content. However, when the water–cement ratio exceeds a threshold value, stone content decreases. Furthermore, the threshold value of the water–cement ratio decreases with increasing water-reducer dosage. Without the addition of the water reducer, as the water–cement ratio increases the overall integrity of the grout stone decreases. The addition of the water reducer alters the surface pore distribution, wherein “uniform small pores” change to “localized large pores.” Based on the multi-objective optimization of Matlab, the recommended optimal mix composition for a slow-setting cement slurry is a water–cement ratio of 0.25 and water-reducer dosage of 1.5%. With the use of this optimized mix composition, the stone content and compressive strength increase by 7.8% and 145.6%, respectively, compared to those obtained using the recommended mix ratio in the specifications. Additionally, all relevant performance parameters meet the requirements specified by previous standards.

This study proposes a comprehensive framework, based on an upper-bound approach, for assessing how vegetation enhances wall stability through two primary mechanisms. The two mechanisms are reinforcement from root systems and hydrological reinforcement through transpiration-induced soil suction. Both contributions are integrated as additional internal energy dissipation terms within a logarithmic-spiral failure model. New expressions of earth pressure in unsaturated soil are derived, considering the influence of vegetation. The active earth pressure acting on the retaining wall is obtained using sequential quadratic programming. The proposed method is validated against classical non-vegetated solutions, confirming its accuracy. The results show that vegetation significantly reduces active earth pressure, with the extent of reduction depending on soil type, root distribution, and transpiration rate. In clay soils, both mechanical and hydrological effects are important, while in sandy soils, mechanical root reinforcement plays the dominant role. The effectiveness of vegetation is influenced by root depth, density, and diameter, with practical design insights provided through parametric charts. This work offers a theoretically consistent and design-oriented tool for evaluating vegetated retaining walls, emphasizing the coupled hydro-mechanical interactions between plants and soil.