Shear strength behaviour of cohesive soils reinforced with vegetation

Vegetation has a great importance in slope stabilization and erosion control, protecting and restraining the soil (at the surface) and increasing the strength of the soil mass (at depth). This paper presents the results of an experimental study developed by CESI S.p.A. particularly focused on the quantitative determination of the increase in soil shear strength due to root systems of four kinds of perennial gramineous plants (Eragrass, Elygrass, Vetiver and Pangrass), imported from abroad and under experimentation in Italy. In order to quantify the contribution of roots to soil mechanical properties, direct shear test on undisturbed samples containing only soil and soil with roots, respectively, were carried out in laboratory. By direct comparison of the tests executed on soil without roots and with roots, it was possible to evaluate the roots' contribution and to underline the direct correlation between the increase in soil shear strength and the root tensile strengths. The results are in good accordance with the few references found in literature and demonstrate the reinforcement capability of the tested plant roots, particularly for stabilization of the superficial soil layers.