Interaction of long rooted grass with natural unsaturated pyroclastic soils: New tests

The hydromechanical response of vegetated soil is a relevant issue for the design of nature- inspired solutions. Cuomo et al. [1] highlighted that artificially vegetated soils can contribute to reduce the volume of debris avalanches and that numerical simulations need experimental results among the inputs. In this paper, root-soil interaction is presented for three different long-rooted grass species and for the Vesuvian pyroclastic soil of southern Italy. The experimental program includes both in situ and experimental tests. In the field, soil suction and water content were measured, and samples were collected periodically in both the original and vegetated soils. Subsequently, laboratory geotechnical tests were performed on unsaturated original samples and on undisturbed vegetated samples. The experimental results are interpreted considering that a non-saturated vegetated soil contains not only air, water and solid phases, but also an additional phase associated with the occupation of the roots in the porous space of the soil, which modifies the porosity of the soil. In addition, a perpendicular root reinforcement model is adopted, which implies that the ratio between root area and root volume coincides. These assumptions are used to estimate the effect of root reinforcement on the shear strength and water retention curve.