The main objective of the research is to link granular physics with
the modelling of rock avalanches. Laboratory experiments consist
to find a convenient granular material, i.e. grainsize and physical
behaviour, and testing it on simple slope geometry. When the appropriate
sliding material is selected, we attempted to model the debris avalanche
and the spreading on a slope with different substratum to understand
the relationship between the volume and the reach angle, i.e. angle
of the line joining the top of the scar and the end of the deposit.
For a better understanding of the mass spreading, the deposits are
scanned with a laser scanner. Datasets are compared to see how the
grain size and volume influence a debris avalanche. The relationship
between the roughness and grainsize of the substratum shows that
the spreading of the sliding mass is increased when the roughness
of the substratum starts to be equivalent or greater than the grainsize
of the flowing mass. The runout distance displays a more complex
relationship, because a long runout distance implies that grains
are less spread. This means that if the substratum is too rough the
distance diminishes, as well if it is too smooth because the effect
on the apparent friction decreases. Up to now our findings do not
permit to validate any previous model (Melosh, 1987; Bagnold 1956).