State-of-the-art review on plant-based solutions for soil improvement

Vegetation has been used as a means in geotechnical engineering for soil improvement and erosion control. This paper aims to present a state-of-the-art review and future prospective on soil improvement and reinforcement with plants, mainly from a perspective of plant mechanical effects. The mechanics of roots and root-soil composite are reviewed with regard to experiments, including root mechanical tests, direct shear tests, pullout tests and triaxial tests. Various factors influencing root reinforcement are characterized and discussed to explain root-soil interactions and related soil strengthening mechanisms. Considering cost and efficiency, extreme climates, and the conflicting mechanisms of plant growth and soil improvement, researchers have introduced nature-based water-soluble polymers (WSPs) into soil improvement to promote vegetation establishment and provide additional binding strength between soil particles. Despite the benefits, existing related researches and concepts are scarce, and there is still a significant knowledge gap in the coupling effect of WSP and plants for soil improvement. The review indicates that the combination of vegetation and WSP has the potential to create “trade-off” and “complementarity” for progressive soil improvement. Finally, new research topics in the field of soil improvement with plants are identified in the review.