Model Test Study of the Influence of Rainfall Intensity and Soil Permeability on Slope Instability

Rainfall intensity and slope soil permeability influence rainfall infiltration and therefore play an important role in deciding the failure mode of rainfall-induced landslides. To investigate the combined effect of rainfall intensity and soil permeability on slope failure mechanisms, a total of 23 model slope tests were performed. Four different sands with permeabilities spanning two orders of magnitude were used to form the sand slope and artificial rainfalls with 9 different intensities were simulated with a calibrated raining device. A combination of photography and soil moisture content measurements was adopted to study the mechanisms of different modes of slope failures occurred within the test series. It is shown that the failure mode of slope transits from retrogressive failure to surface slide and to flow slide with the increase of rainfall intensity. Because rainfall largely transformed to surface runoff in tests with very small slope permeability (e.g., < 7 × 10 −6 m/s), these slopes failed due to surface scour and erosion. Except for these tests where surface runoff was dominant, the failure mode of soil slope is controlled by the soil resistance to shearing and flow when the failure occurs, which is in turn controlled by the water content reached in the main slope body at the onset of failure ( ω f ) and the soil water characteristics. ω f increases with the increase of rainfall intensity and the decrease of soil permeability.