Three-dimensional numerical analysis of plant-soil hydraulic interactions on pore water pressure of vegetated slope under different rainfall patterns

Understanding the pore water pressure distribution in unsaturated soil is crucial in predicting shallow landslides triggered by rainfall, mainly when dealing with different temporal patterns of rainfall intensity. However, the hydrological response of vegetated slopes, especially three-dimensional (3D) slopes covered with shrubs, under different rainfall patterns remains unclear and requires further investigation. To address this issue, this study adopts a novel 3D numerical model for simulating hydraulic interactions between the root system of the shrub and the surrounding soil. Three series of numerical parametric studies are conducted to investigate the influences of slope inclination, rainfall pattern and rainfall duration. Four rainfall patterns (advanced, bimodal, delayed, and uniform) and two rainfall durations (4-h intense and 168-h mild rainfall) are considered to study the hydrological response of the slope. The computed results show that 17% higher transpiration-induced suction is found for a steeper slope, which remains even after a short, intense rainfall with a 100-year return period. The extreme rainfalls with advanced (PA), bimodal (PB) and uniform (PU) rainfall patterns need to be considered for the short rainfall duration (4 h), while the delayed (PD) and uniform (PU) rainfall patterns are highly recommended for long rainfall durations (168 h). The presence of plants can improve slope stability markedly under extreme rainfall with a short duration (4 h). For the long duration (168 h), the benefit of the plant in preserving pore-water pressure (PWP) and slope stability may not be sufficient.