Geotechnical and hydrological characterization of hillslope deposits for regional landslide prediction modeling

We attempt a characterization of the geotechnical and hydrological properties of hillslope deposits, with the final aim of providing
reliable data to distributed catchment-scale numerical models for shallow landslide initiation. The analysis is based on a dataset
built up by means of both field tests and laboratory experiments over 100 sites across Tuscany (Italy). The first specific goal is to
determine the ranges of variation of the geotechnical and hydrological parameters that control shallow landslide-triggering
mechanisms for the main soil classes. The parameters determined in the deposits are: grain size distribution, Atterberg limits,
porosity, unit weight, in situ saturated hydraulic conductivity and shear strength parameters. In addition, mineral phases recog-
nition via X-ray powder diffraction has been performed on the different soil types. The deposits mainly consist of well-sorted silty
sands with low plastic behavior and extremely variable gravel and clay contents. Statistical analyses carried on these geotechnical
and hydrological parameters highlighted that it is not possible to define a typical range of values only with relation to the main
mapped lithologies, because soil characteristics are not simply dependent on the bedrock type from which the deposits originated.
A second goal is to explore the relationship between soil type (in terms of grain size distribution) and selected morphometric
parameters (slope angle, profile curvature, planar curvature and peak distance). The results show that the highest correlation
between soil grain size classes and morphometric attributes is with slope curvature, both profile and planar.