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.

The suction caisson serves as an important anchoring foundation for floating platforms, widely used in deep-sea oil/gas platforms and offshore wind turbines due to its convenient construction, cost-effectiveness, and structural reliability. This study, based on the scaled model tests conducted in saturated sand under displacement control, investigates the uplift bearing capacity, ultimate failure modes, and pore pressure evolution pattern of suction caissons under varying loading rates and aspect ratios. The results indicate that: 1) Under fully drained conditions, the main uplift resistance of the suction caisson is derived from structural self-weight and sidewall friction, with negligible contributions from internal negative excess pore pressure and minimal loading rate effects on the bearing capacity; 2) Under partially drained conditions, the uplift bearing capacity increases correspondingly with the growth of negative pressure, demonstrating significant influence of negative pressure on load-bearing performance; 3) Within a certain range, as the aspect ratio increases, the dissipation rate of pore pressure decreases while the sidewall friction resistance enhances, leading to substantial improvement in ultimate uplift capacity.

This study mechanistically investigats slope stability under delayed-peak heavy rainfall infiltration. We develop a theoretical framework for unsaturated soil seepage using the two-dimensional Richards equation, with exponential function models characterizing both soil-water characteristic curves and hydraulic conductivity functions. During intense rainfall events, flux boundary and constant pressure head boundary conditions were applied to simulate the complete infiltration and surface runoff phases, respectively. Through rigorous mathematical derivation, we obtained a spatiotemporal analytical solution for delayed-peak heavy rainfall infiltration that accounts for surface runoff dynamics. The proposed analytical solution was verified through finite element simulations using Geostudio-Seep/W software. Subsequently, the temporal-spatial evolution characteristics of slope stability under five distinct rainfall scenarios were systematically investigated employing Fredlund's dual-stress variable strength theory. The principal findings include: 1) the initial rainfall phase significantly influences slope stability degradation; 2) the runoff-to-total rainfall ratio positively correlates with rainfall intensity; and 3) the safety factor shows strong spatiotemporal coupling with pore water pressure distribution patterns.

This study takes the high slope of Maiwan Water Conservancy Hub in Tunchang County, Hainan Province as the research object, focusing on the challenges of identifying parameters for the unsaturated seepage intrinsic models. Utilizing wireless transmitter, data acquisition instruments, and other monitoring devices, on-site slope infiltration experiments were conducted. The collected monitoring data were combined with the differential evolution method to perform a global inversion of the Van Genuchten model's parameters ( $\alpha$, $n$, ${\theta }_{\text{s}}$, ${\theta }_{\text{r}}$, $K_{\text{s}}$). A finite element model was established using PLAXIS software for numerical simulation, analyzing the variation patterns of simulated values and comparing them with measured values to validate the reliability of the inverted parameters. The results demonstrate that the numerical simulations driven by the inverted parameters exhibit high consistency with the measured data, with errors at each depth remaining within 5%. Experimental verification confirms the accuracy of the numerical simulations, providing a parameter basis for unsaturated seepage studies in tropical slopes and a reference for determing unsaturated hydraulic parameters in similar soils.