Hydro-Mechanical Performance of Vegetated Porous Concrete in Tropical Soils under Rainfall-Induced Slope Instability

Rainfall-induced slope failures in tropical regions with lateritic soils pose significant geotechnical risks, which are exacerbated by increasingly frequent extreme rainfall events. While vegetated porous concrete (VPC) has emerged as a sustainable reinforcement strategy, its integrated hydro-mechanical behavior under varying rainfall intensities has not been systematically evaluated. This study evaluates the hydro-mechanical performance of VPC under rainfall infiltration using numerical and physical modeling, and compares its effectiveness with unreinforced, root-reinforced, and porous concrete (PC)-reinforced slopes. Numerical simulations were used to quantify the factor of safety (FoS) and slip surface formation under both dry and rainfall conditions. Physical models of unreinforced slopes were subjected to simulated high-intensity rainfall (250 mm/day) and low-intensity rainfall (50 mm/day for five days). Volumetric water content (VWC), pore-water pressure (PWP), and soil loss were monitored, and manual sampling was used to verify the moisture distribution. The results revealed that rainfall intensity governed the slope response: high-intensity rainfall triggered rapid suction loss and general failure within 15 min, whereas low-intensity rainfall led to only localized deformation and light rilling without collapse. VWC and PWP trends revealed faster wetting at the mid-slope than at the crest and toe positions, with suction persisting under low-intensity rainfall conditions. Soil loss was highly dependent on rainfall intensity, with high-intensity events resulting in almost tenfold higher erosion rates. Numerical simulations indicated that root and PC reinforcement enhanced slope stability only under dry conditions. In contrast, VPC consistently maintained suction, facilitated pore-pressure dissipation, and restricted slip surfaces to shallow zones, thereby yielding the highest FoS values. These findings demonstrate that VPC provides a dual hydro-mechanical benefits, i.e., mechanical interlocking and preferential drainage, which enhances slope resilience against rainfall-induced failures in tropical soils.