In-situ and laboratory hydro-mechanical tests for assessing the potential effect of vegetation cutting on shallow landslides in the source area of a debris flow

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The paper presents the results of in-situ and laboratory tests aimed at evaluating the effects of tree cutting on shallow soil movements which are considered responsible for sediment recharge in a debris flows source area. The study area (Central Apennines, Italy) was affected by debris flow events in 2012 and 2015, following intense rainfalls. The debris flow source area is close to parcels of beech tree cutting observed in the previous decade on the surrounding steep slopes. Experimental investigations were performed on the rooted and bare soil, to explore the differences in terms of soil shear strength, volumetric behaviour, and water retention properties. A large set of direct shear tests were performed at different hydraulic initial conditions. In the paper, only dry conditions are explored. Roots contributed to enhance the soil shear strength although inducing higher collapse and volumetric strains. In-situ corkscrew tests enabled the measurement of rooted-soil shear strength on the slopes close to the source area. Experimental results were mapped and interpreted within an effective stress formulation for partially saturated soils: even if preliminary, some trends of shear strength decrease were observed within the cut areas.

3rd International Workshop on Soil-Vegetation-Atmosphere Interaction (RootS2025)

2b. Field scale characterisation of the bio-hydro-chemo-mechanical behaviour of rooted soils