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An experimental investigation of the collapse behaviour of an unsaturated compacted soil along the static compaction curves

Al-Khyat, Sahar 2018. An experimental investigation of the collapse behaviour of an unsaturated compacted soil along the static compaction curves. PhD Thesis, Cardiff University.
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Unsaturated compacted soils are used in many civil engineering works, such as earth dams, embankments, soils beneath foundations and pavements. A major problem encountered with these soils is the tendency to collapse upon wetting under certain conditions. There has been extensive research into the collapsibility of compacted soils. However, comprehensive investigation into the hydro-mechanical behaviour of unsaturated compacted soils under various loading, wetting and compaction conditions is needed for the engineers to devise safe and cost-effective solutions to such problem. The outcomes of such a study also provides a wider perspective on soil collapsibility and generate geotechnical data and parameters useful for establishing and validating constitutive models. This thesis presents a laboratory-based experimental study of the collapse behaviour of compacted soil mixtures of 40% silt, 40% sand and 20% clay. Series of laboratory tests were conducted including basic characterisation, static compaction behaviour, suction measurements, single and double-oedometer tests, and suction-controlled oedometer tests under wetting. In this context, a new static compaction testing procedure is developed for establishing static compaction curves of the soil both in terms of applied compaction pressure and compaction energy. One-dimensional volume change behaviour of compacted samples along the established static compaction curves was explored. Statically compacted specimens with various compaction conditions were subjected to a wide range of vertical stresses. The compatibility of various controlled-suction wetting tests was also explored. The experimental data obtained were analysed in terms of collapse strain and soil-water characteristic curves (SWCC) based on theories of unsaturated soil mechanics. The proposed procedure of the static compaction tests showed the potential effectiveness in establishing static compaction curves at various levels of compaction energy and pressure. The static compaction pressure required to transmit constant compaction energy was found to decrease with increasing the water content of specimens, whereas increased compaction energy was observed along the compaction pressure curves. The static compaction was also found to induce suction changes of specimens. The study generated new knowledge in the form of linking the compaction effort with the collapse behaviour at a various range of applied vertical stresses and suction. The collapse behaviour of compacted specimens along the static compaction curves was found to be predominantly controlled by the applied compaction pressure during specimen preparation. Similarly, the wetting SWCCs of compacted specimens along the static compaction curve were found to be strongly influenced by the static pressure of compaction at low suctions.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Static compaction; Collapse strain; Suction-Controlled Oedometer; Wetting path; Suction contour; Effective stress.
Date of First Compliant Deposit: 14 January 2019
Last Modified: 05 Aug 2021 15:28

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