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Experimental study of volume change and shear strength behaviour of statically compacted collapsible soil

Almahbobi, Suhad 2018. Experimental study of volume change and shear strength behaviour of statically compacted collapsible soil. PhD Thesis, Cardiff University.
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Collapsible soils present significant geotechnical and structural engineering challenges. These soils are known to withstand relatively high stresses at unsaturated state. Upon exposure to a saturation front at a constant surcharge, the volume change of such soils usually occurs within a short time period. It has been shown that the magnitudes of collapse strain and the shear strength depend upon the applied stress and suction. This thesis presents an experimental study of the effects of confining stress and suction on volume change and shear strength behaviour of a collapsible soil. Laboratory tests were carried out on statically compacted soil specimens. A mixture of M400 silt (40%), Leighton Buzzard sand (40%) and 20% Speswhite kaolin was considered for preparing the soil. The percentages of various particle-size fractions in the soil are similar to that is found in naturally occurring aeolian soil deposits. A series of single and double oedometer tests have been carried out to investigate the effects of different compaction parameters, such as initial water content, initial dry unit weight, compaction pressure and overburden pressure on the collapse strain. Wetting tests under isotropic stress conditions and consolidated drained triaxial shearing tests were carried out to study the impact of confining stress (100, 250 and 400 kPa) on the volume change and shear strength of the statically compacted soil specimens at several suction during the wetting process. The suction – degree of saturation relationship at high suctions from chilled-mirror dew-point tests and the test results from the wetting tests (based on the water volume and total volume changes) enabled establishing the SWCCs. The relationship between suction and suction stress (i.e., suction stress characteristic curve, SSCC) was established from the wetting water retention data at various applied confining stresses and suctions. Similarly, the SSCC was established based on the shear strength test data. The results indicated that the impact of confining stress on the volumetric strain and wetting SWCCs of the soil was distinct. The SWCCs in terms of water content were affected the applied confining stress; however, the differences in the SWCCs in terms of the degree of saturation were found to be insignificant. As the soil underwent the wetting process (a decrease in soil suction), the friction angle (∅′) decreased slightly, the cohesion value decreased non-linearly, and the angle ∅

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Collapsible soil; Volume change; Shear strength; static compaction; Soil-water characteristic curve (SWCC); Suction stress; Effective stress.
Date of First Compliant Deposit: 14 January 2019
Last Modified: 14 Jan 2019 13:01

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