On the measurement of in situ unsaturated shear strength of a beech-rooted soils

This paper presents some preliminary results of a study aimed at assessing the effect of vegetation cutting on landslide phenomena. Two debris flow events occurred in the study area, located close to Nottoria village (Perugia, Central Italy) in 2012 and 2015. These landslides occurred following rainfall events in an incised valley characterised by steep slopes, vegetation cuts and the presence of debris beds originating from the alteration of limestone. A methodology was developed to assess and interpret the in- situ shear strength of unsaturated vegetated and fallow soils belonging to the slopes surrounding the propagation channel and source area of the debris flow. Corkscrew and water retention measurements were carried out in-situ whereas laboratory results showed a marked heterogeneity of the soils present on the study area. Hence, the interpretation of the reinforcement results considered soil heterogeneity, an effective stress formulation for unsaturated soils as well as a vegetation’s soil reinforcement model provided in literature, obtaining comparable results with other scientific observations.