Mechanism and modelling of shallow soil slope stability during high intensity and short duration rainfall

Shallow landslides in nearly saturated uncohesive to slightly cohesive soils are triggered by high intensity, short duration rainfall which infiltrates into soil and changes intergranular friction and effective stresses. For this, the especially developed Soil–Water Interaction Modelling System (SWIMS) was used with CL-ML type soils. For simplicity, rainfall intensity and duration were kept constant. Results showed that (1) All 35°35° slopes were failed by translational failure. For the other (15°,25°)(15°,25°) slopes, no failures were observed; (2) For all slopes, FOS increased with increasing compaction degree and decreased with increasing slope angle; (3) Other parameters, such as soil density, porosity, saturation degree, water contents, and water permeability may also affect shear strength/slope stability, especially for low degrees of saturation (S<95%)(S<95%), compared to high degrees of saturation (S=,>95%)(S=,>95%). (4) A correlation of SWIMS tests observed that average wetting band depths (hobser), with the calculated wetting band depths from the Lump Equation (hLE)(hLE), were poor, as hobser values were much higher than hLEhLE values. Differences increased for very low degrees of saturation (S)(S), compared to S>95%S>95%. This meant that the Lump equation underestimated wetting band depths. Further, if the Lump equation is still considered valid, this would imply either water-permeability increases, porosity decreases or both occur towards full saturation; a process where the last possibility is the most probable occurrence.