Effects of Residual Soil Characteristics on Rainfall-Induced Shallow Landslides Along Transport Arteries in Bac Kan Province, Vietnam

Abstract

Slope failures depend strongly on the geotechnical properties of soils and rocks. Therefore, thresholds of rainfall-induced landslides vary according to changes in soil properties. This study assesses the effects of residual soil characteristics on 73 rainfall-induced shallow landslides along three main routes in Bac Kan province, Northeast Vietnam. All of these landslides occurred during or after torrential rains. Of the total number of landslides, 71 were shallow rotational and translational slides. They occurred in residual soils of silty sand (SM), silt with sand (ML), and elastic silt (MH), among which SM was the most dominant. Rain infiltration modeling and deterministic and probabilistic analyses of slope stability were used to assess the effects of soil permeability, strength, thickness of residual soils and slope excavation on rainfall-induced shallow landslides. The slopes constituted by the SM soil type were more vulnerable to rainfall-induced shallow landslides than the ML and MH types due to its higher mean saturated hydraulic conductivity. Shallow translational and rotational earth slides were dominant on cut slopes when the thickness of the residual soils was less than 1.5 m and greater than 2.5 m, respectively. Slope excavation in the study area decreased the factor of safety by 20%. Three thresholds of rain intensity-duration (ID) were defined for deterministic stability analysis (ranging between extremely high and low landslide hazard levels): I = 204.47 D−1.073, I = 174.91 D−1.039 and I = 133.34 D−0.981.