GRAPEVINE ROOTS STRENGTH IN AN AREA SUSCEPTIBLE TO SHALLOW LANDSLIDES FOR SLOPE STABILITY ASSESSMENT

INTRODUCTION. In the area of Oltrepo Pavese (Lombardy), in northern Italy, several rainfall-induced shallow landslides, usually developed in the first few meters of soil, affected in the last five years hilly slopes cultivated with vineyards. These phenomena caused the destruction of the vineyards and the loss of high productivity soils. For this reason studying the contribution of the grapevines, and in particular of their roots, is fundamental for soil mechanical reinforcement. Many studies demonstrated the contribution of forest and natural vegetation, while most of the studies usually neglected the potential contribution of cultivated plants to slope stability. The objectives of this work were to estimate the grapevine roots strength and distribution pattern in soil for the assessment of grapevine roots contribution to soil shear strength and to slope stability. MATERIALS AND METHODS. A multidisciplinary study was carried out for characterizing the roots and soils where they live. In different test-site slopes characterized by vineyards of different age affected or not by shallow landslides several pits were excavated to collect root samples for mechanical properties measurement and for evaluating root density and size distribution with depth. Pedological profiles were accurately determined in the pits and soil samples for geotechnical characterization were also collected at different depths. Root mechanical properties were measured through laboratory tensile tests in terms of tensile force and were used to estimate the contribution of the roots to the shear strength of the soil by applying the Fiber Boundle Model (FBM). RESULTS AND DISCUSSION. Grapevine roots mechanical properties and distribution were compared between the test-site slopes. There is a certain degree of similarity on grapevine roots tensile resistance considering different age vineyards and slopes affected or not by shallow landslides. RAR, number of roots and root reinforcement along depth showed a great in-situ variability linked also with plant age, and lowest values at the soil-bedrock contact, regardless the depth of this contact. CONCLUSIONS. The study allowed for the estimation of the contribution of grapevine roots to soil shear strength. The results could have significant repercussions on land use planning because they allow for the identification of vineyard slopes prone to shallow landslides and on land management for improving agricultural best practices which can prevent instability phenomena.