Exploring stress-paths and vegetation reinforcement mechanisms in a compacted soil

The use of vegetation is a sustainable technique to mitigate the risk of landslides and erosion phenomena. Literature agrees that roots improve soil shear strength properties. The reinforcement of roots on soils is complex and depends on their morphological and mechanical characteristics and the stresses that develop at the soilroot interface. In this regard, many models have been produced in literature to infer the increase in soil shear/tensile strength due to roots. Among them, soil hydraulic state was poorly considered. Large cell triaxial consolidated drained compression tests and tensile tests were carried out to explore the mechanical effects of vegetation on a compacted soil at low confining stresses and at different hydraulic states (identified in terms of suction and degree of saturation). Root features were thoroughly assessed for each soil specimen and were correlated, jointly with soil hydro-mechanical states, to the two soil reinforcement mechanisms observed (roots breakage and slippage). Different stress-strain responses were observed during the mechanical tests, depending on soil initial suction. Strain spatial distributions during tensile tests were observed by an advanced imaging technique (Particle Image Velocimetry): roots contributed to redistribute the tensile stresses over larger soil volumes. A combination of two literature reinforcement models was adopted to interpret the results: one model to consider root tensile strength full exploitation and breakage, and the other to predict friction forces at the soilroot interface during root slippage. The correlation coefficients of these two models were calibrated based on this experimental campaign. Fraccica, A., Romero Morales, E. E., Fourcaud, T. (2019). Multi-scale effects on the hydraulic behaviour of a root-permeated and compacted soil. InIS-Glasgow 20197th International Symposium on Deformation Characteristics of Geomaterials(pp. 1-5). EDP Sciences. Fraccica, A., Romero, E., Fourcaud, T. (2022). Tensile strength of a compacted vegetated soil: Laboratory results and reinforcement interpretation.Geomechanics for Energy and the Environment,30, 100303. Fraccica, A., Romero, E., Fourcaud, T. (2023). Large cell triaxial tests of a partially saturated soil with vegetation. InE3S Web of Conferences(Vol. 382, p. 05005). EDP Sciences. Fraccica, A., Romero, E., Fourcaud, T. (2024). Effects of vegetation growth on soil microstructure and hydro-mechanical behaviour.Gotechnique (accepted) Oorthuis, R., Hrlimann, M., Fraccica, A., Lloret, A., Moya, J., Puig-Polo, C., Vaunat, J. (2018). Monitoring of a full-scale embankment experiment regarding soilvegetationatmosphere interactions.Water,10(6), 688.