Abstract
The critical rainfall conditions triggering topsoil failures on slopes are presented with functional relationships include the strength parameters (C, Φ), saturated coductivity (Ks), steepness (θ), soil depth (D) and length (L) of the hillslopes. On the basis of the virtical one-dimensional slope stability analysis and the sectional two-dimensional kinematic-wave runoff analysis with Darcy's low, rainfall thresholds are derived as follows.
Value of the cumulative rainfall threshold (Rc) depends on the C, Φ, D, θ and effective porosity (w') . Value of the rainfall intensity threshold depends on C, Φ, Ks, D, θ and L. The threshold curve on cumulative rainfall-intensity relationships derived with the initial water loss medel, accounting water absorption through virtical unsaturated infiltration, can be fit firly well in the other threshold curve which had been derived from the response analysis for slope failures in Japan using the antecedent rainfall index.
