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 (4h 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.

The hydrological response of groundwater to rainfall plays a key role in the initiation of deep-seated bedrock landslides; however, the mechanisms require further investigation due to the complexity of groundwater movement in fissured bedrock. In this study, an active translational landslide along nearly horizontal rock strata was investigated. The hydrological response of groundwater to rainfall was analyzed, using the data from a four-year real-time field monitoring program from June 2013 to December 2016. The monitoring system was installed along a longitudinal of the landslide with severe deformation and consisted of two rainfall gauges, nine piezometers, three water-level gauges, and two GPS data loggers. Much research effort has been directed to exploring the relationship between rainfall and groundwater response. It is found that both the pore-water pressure (PWP) and groundwater level (GWL) responses were significantly influenced by the rainfall pattern and the hydrological properties of the underlying aquifer. The rapid rise and fall of PWP and GWL were observed in the rainy season of 2013 with high-frequency, long-duration, and high-intensity rainfall patterns, especially in the lower of the landslide dominated by the porous aquifer system. In contrast, a slower and prolonged response of PWP and GWL to rainfall was observed in most monitoring boreholes in 2014 and 2015 with two rainstorms of short duration and high intensity. In the lower of the landslide, the peak GWL exhibited a stronger correlation with the cumulative rainfall than the daily rainfall in a single rainfall event whereas the peak groundwater level fluctuation (GWLF) exhibited a strong correlation with API with a half-life of 7 days. In the middle of the landslide, however, relatively lower correlation between rainfall and groundwater response was observed. Three types of groundwater flow were identified based on the recession coefficients of different segments of water-level hydrographs in the landslide area, corresponding to the quick flow through highly permeable gravely soil and well-developed vertical joints in the bedrock, the slow and diffuse flow through the relatively less-permeable bedrock, and the transition between them in the aquifer system.