Influence of grass roots on shear strength of pyroclastic soils

Abstract

This paper investigates the effects of indigenous vegetation on the shear strength of loose pyroclastic soils of the Campania region (southern Italy); these soils are frequently affected by shallow landslides 1–2 m deep that experience static liquefaction during the post-failure stage. Perennial graminae grasses were seeded in a one-dimensional column 2 m high and filled by pyroclastic soils, allowing the root to grow under atmospheric conditions. A noninvasive sampling procedure was adopted to take the vegetated soil samples, in which the roots were in their natural geometrical distribution. For each rooted sample, the root biomass, RM, was measured and the root volume density, RVD, was calculated. Isotropic consolidated triaxial tests in both drained and undrained conditions were performed on the rooted specimens, as well as on bare specimens as a control. The obtained results showed that the roots generally provided an increment to the soil strength. In drained conditions a reduction in the volumetric deformation was observed, which, under undrained conditions, was reflected in a general reduction of the excess pore-water pressures with a possible inhibition of the static liquefaction occurrence. This study highlights the potential role of grass roots as bio-engineering practice for stabilizing shallow covers of pyroclastic soils.