Mechanical and anti-seepage properties of tropical soil slopes reinforced synergistically by MICP and selected plants

To enhance the stability of tropical soil slopes, avoid the limitations of single reinforcement techniques, and develop green, low-carbon reinforcement techniques, this study investigates the feasibility of synergistically reinforcing low-liquid-limit clay using microbial induced calcium carbonate precipitation (MICP) and selected plants. Three typical tropical plants were selected, and carpet grass was identified as the most adaptable through simulations of tropical light, temperature, and post-MICP soil conditions, with its suitable cementation solution concentration range determined to be 0.2-0.6 mol/L. Direct shear, unconfined compression strength (UCS), and permeability tests were subsequently conducted, combined with SEM, EDS, and XRD microanalyses, to systematically evaluate the macroscopic properties and underlying mechanisms of the synergistic reinforcement. The results indicate that after the MICP-plant synergistic treatment, the soil's cohesion, internal friction angle, and UCS increased by 145.9%, 100.4%, and 161.8%, respectively, compared to the untreated group, while the permeability coefficient decreased to 6.81×10^-8 m/s, representing an improvement in anti-seepage performance by approximately two orders of magnitude. Microscopic analysis reveals that the calcium carbonate precipitated by MICP and the plant roots formed a “cementation-reinforcement” composite structure, which not only filled soil pores but also enhanced the anchorage effect at the root-soil interface. The synergistic effect of MICP and plants not only significantly enhanced the mechanical properties of tropical low-liquid-limit clay but also substantially improved its anti-seepage performance, effectively mitigating slope instability caused by rainfall infiltration and erosion under tropical storm conditions.