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Experimental study of collapse mechanisms in gravelly soils

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Title: Experimental study of collapse mechanisms in gravelly soils
Authors: Elhusain, Luai
Item Type: Thesis or dissertation
Abstract: Unusual collapsible gravelly soils from Khartoum, Sudan, have led to severe structural damage, usually caused by water infiltration into the underlying ground. As taking undisturbed block samples of the natural soil was not possible because of its friable gravelly nature, analogue specimens were prepared from lightweight aggregate (Lytag) bonded with kaolin. Results from previous studies did not predict degrees of ‘collapse potential’ (CP) levels that correspond to the severe damage observed. A theoretical procedure is developed, based on differences between in-situ soil density and the maximum compacted density, which resulted in a more realistic magnitudes of CP (ratio of collapse settlement to layer thickness). The primary research focus involved an experimental programme, developed in three stages using analogue specimens. First, the effectiveness of conventional 1-D collapse tests was assessed. Second, larger diameter analogue specimens were tested under different boundary conditions with (a)full and (b)partial lateral confinement (similar to footing tests). The latter tests produced far more realistic collapse (10x the 1-D tests, i.e., from moderate to severe CP). Consequently, the third approach was to test under triaxial conditions, with careful control of lateral and deviatoric stresses (close to those in situ), and allowing axial, volume and radial collapse strains to be determined. Test boundary conditions strongly govern the magnitude of CP and collapse mechanism. Two different collapse mechanisms were identified. At high deviatoric stresses and low confining stresses, when the specimen was inundated, there was radial dilation, while radial contraction occurred under low deviatoric stresses and high confining stresses. The severity of CP increases with inundation collapse stress. A relationship between collapse strain and resulting increased collapse density with inundation collapse stress is developed: at constant cell pressures, this relation has a unique curve which can be used to classify the collapse mechanisms; a soil collapse classification chart is proposed.
Content Version: Open Access
Issue Date: Apr-2022
Date Awarded: Jun-2022
URI: http://hdl.handle.net/10044/1/98162
DOI: https://doi.org/10.25560/98162
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: Standing, Jamie
Sponsor/Funder: University of Khartoum
Department: Civil and Environmental Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Civil and Environmental Engineering PhD theses



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