Wetting-induced collapse behaviour of a natural and vegetated coarse pyroclastic soil

Vittoria Capobianco,Vito Foresta,Sabatino Cuomo,Leonardo Cascini,R Cardoso,C Jommi,E Romero

doi:10.1051/e3sconf/202019503025

Vittoria Capobianco, Vito Foresta + Show 5 more

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https://doi.org/10.1051/e3sconf/202019503025

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Abstract

Unsaturated pyroclastic soils originated by Vesuvius volcano show a collapsible behaviour upon wetting with a significant reduction in volume and rearrangement of solid skeleton. The paper investigates the role played by vegetation on wetting-induced collapse behaviour (namely, collapsibility) of reconstituted unsaturated soil specimens through two series of wetting tests in a standard oedometer. The first series of tests was performed on bare soil specimens, as to resemble the site conditions. The second group of tests was conducted on the same soil previously vegetated for 20 weeks with perennial graminae species, which are frequently used as a nature-based solution for contrasting surface erosion along slopes in different geo-environmental contexts. First, an initial small vertical net stress was applied on partially saturated specimens having similar initial saturation degree, then collapse was induced by flooding the specimens with distilled water and final vertical displacements were measured. As main outcome, soil porosity is highly reduced by the growth of grass roots. Consequently, the potential wetting collapse in the rooted soils is inhibited by low values of porosity. For similar initial soil porosity, in both bare and vegetated specimens (after root growth), a further reduction of the volumetric collapse magnitude is observed.

Highlights

Air-fall pyroclastic deposits originated by eruption activities of the Vesuvius district (South Italy) are usually in loose partially saturated conditions [1] by covering the shallowest layers of the hillslopes around the volcanic area [2].During rainfall, water infiltrates the ground and may induce volumetric collapse in loose unsaturated soils
This paper extends the previous investigations to the effect of the roots on collapsible behaviour of pyroclastic soils due to wetting
This work deals with the collapsibility of bare reconstituted specimens of pyroclastic soils and the role played by the presence of roots, belonging to perennial graminae species, on the behaviour of soil undergoing a wetting process

Summary

Introduction

Water infiltrates the ground and may induce volumetric collapse in loose unsaturated soils. The presence of roots in the soil can reduce the deformability of loose soils in unsaturated conditions when subjected to external loading or to wetting during rainfall infiltration. The effect of roots on the deformability of collapsible soils in unsaturated conditions needs to be studied, since limited literature contributions showed that roots could change the soil structure through the occupancy of roots in soil pore space [8, 9] and the production of root exudates [10]. Some authors in the past investigated the effects of external loading or initial suction on the collapsibility of bare pyroclastic soils of Campania region, through standard oedometer tests [11, 12] and suction controlled oedometer tests [13, 14]

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