Wetting can induce the so-called 'capillary collapse' in loose unsaturated soils. Collapse mechanisms have been studied at macro-scale for many years, while few observations at micro-scale are available. In this work, wetting tests were conducted by combining X-ray computed tomography (CT) and image treatment to investigate the soil collapse of volcanic sands of southern Italy at both macro- and micro-scale. The specimens were tested under self-weight and the matric suction was gradually reduced until collapse. Standard techniques and image analysis were used to measure the porosity and degree of saturation for the whole specimen, while image analysis of sub-volumes was done at micro-scale. The X-ray CT-aided wetting tests allowed: (a) the analysis of soil microstructure and its variations, (b) the accurate measurements of porosity and degree of saturation for differently sized representative element volumes (REVs). The local modifications of soil internal structure were measured and compared with the overall behaviour of the whole specimen. The porosity changed both in REV-averaged values and spatial distribution. The degree of saturation increased while keeping similar spatial distribution until collapse. The insights at both micro- and macro-scale provided a rational overview of the complex mechanisms regulating the pre- and post-collapse configuration of soil.

Wetting test and X-ray computed tomography of volcanic unsaturated sands

Moscariello, M.;Cuomo, S.
2019-01-01

Abstract

Wetting can induce the so-called 'capillary collapse' in loose unsaturated soils. Collapse mechanisms have been studied at macro-scale for many years, while few observations at micro-scale are available. In this work, wetting tests were conducted by combining X-ray computed tomography (CT) and image treatment to investigate the soil collapse of volcanic sands of southern Italy at both macro- and micro-scale. The specimens were tested under self-weight and the matric suction was gradually reduced until collapse. Standard techniques and image analysis were used to measure the porosity and degree of saturation for the whole specimen, while image analysis of sub-volumes was done at micro-scale. The X-ray CT-aided wetting tests allowed: (a) the analysis of soil microstructure and its variations, (b) the accurate measurements of porosity and degree of saturation for differently sized representative element volumes (REVs). The local modifications of soil internal structure were measured and compared with the overall behaviour of the whole specimen. The porosity changed both in REV-averaged values and spatial distribution. The degree of saturation increased while keeping similar spatial distribution until collapse. The insights at both micro- and macro-scale provided a rational overview of the complex mechanisms regulating the pre- and post-collapse configuration of soil.
2019
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4735864
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