Landslides involving debris covers, i.e. those deposits deriving from the weathering and mechanical fragmentation of the bedrock, are generally characterized by a considerable longitudinal extension compared to the thickness of the material involved. This type of landslide can be effectively analyzed through the infinite slope method (Skempton, 1957). The application allows calculating the critical thickness of a debris cover, the minimum time necessary for the saturation of the critical thickness to occur, and all possible combinations of duration and rainfall intensity that can trigger, in the considered slope, a landslide with a frequency equal to the return period of the climatic curve.
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The minimum time necessary for the saturation of the critical thickness to occur is calculated using the Green and Ampt (1911) infiltration model:
tmin[ore]=(∆φ/k)·[hcrit-pris·ln((pris+hris)/pris)]
Where:
∆φ represents the residual effective porosity given by (1-s) φ, where s is the initial degree of saturation of the soil and φ is the effective porosity;
k (mm/hour) soil permeability;
hcrit (mm) critical thickness;
pris (mm) resaturation pressure, which can be estimated with the relation 12/d10, d10 is the diameter of the 10% passing.
For a given duration value, the minimum rainfall intensity to create a saturation front is calculated with the expression:
imin[mm/ore]=(∆φ/t)·[hcrit-pris·ln((pris+hris)/pris)]·[(hris+pris)/hris]