- Title
- Influence of physico-chemical interactions on sample quality in soft soils
- Creator
- Ouyang, Kaiwen
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Sample quality assessment is becoming more relevant within the characterization of natural soft ground. Cost-effective designs are based on high-quality soil parameters which, in the majority of cases, can only be obtained using advanced sampling and testing methods. Recent improvements to standards for sampling in soft soils have focused almost entirely to reducing mechanical sampling disturbance, i.e., that caused by the penetration and retrieval of the tube sampler in the ground. However, the phenomenon of sampling disturbance is more complex than that and cannot be tackled by simply considering mechanical effects. There are several stages of the sampling process that impose mechanical (stress relief, tube penetration and extraction, soil extrusion) but also hydraulic (tube penetration and extraction, tube sealing using wax, transport and storage, soil extrusion), thermal (tube sealing using wax) and sometimes (bio)chemical (tube sealing and tube storage) paths which are coupled. Most of these effects have largely overlooked over the past decades, perhaps due to the lack of appropriate experimental techniques and theories capable of capturing those rather complex thermo-hydro-(bio)chemo-mechanical (THCM) interactions. In Australia, rigorous guidelines for undisturbed sampling in soft soils are still not available. The selection of the sampler type is merely mentioned, the use of wax as sealing method for tube specimens is suggested without recommendations and storage methods, a key aspect due to the potential activation of biogeochemical processes, is also overlooked. From an international perspective, just a few recent studies have tried to investigate the storage effect whereas waxing has received almost no attention. To fill in this gap in knowledge, this thesis presents the results of a comprehensive experimental and numerical study on the effects of the transient thermal loading caused by waxing as well as the storage effect in Ballina clay, a very high plasticity estuarine Australian soft clay from New South Wales encountered at the National soft soil Field Testing Facility (NFTF) located in Ballina northern NSW. Three main aspects were studied in this research: (i) the development of a simple non-destructive tool to assess sample quality based on CT scanning, (ii) the evaluation of thermal loading effects imposed by waxing on the behaviour of soft soils, and (iii) the assessment of long-term storage on soft soil behaviour. Thermal loading (waxing) tests, carried out on reconstituted and natural specimens of Ballina clay, where combined with advanced numerical simulations using the numerical codes ABAQUS® and CODE_BRIGHT® in an attempt to understand the thermal, hydraulic and mechanical response of the soil upon waxing. Additional tube specimens were retrieved from the NFTF and used in subsequent laboratory testing to evaluate the influence of the storage time on soil properties. The maximum storage time prior testing was 1 year. In both cases, mechanical tests (Constant Rate of Strain oedometer tests and triaxial tests) were combined with Mercury Intrusion Porosimetry (MIP) testing and geochemical analysis to evaluate the consequences of waxing and storage time on mechanical properties and soil microstructure.
- Subject
- soft soil; sample quality; non-destructive sample quality assessment; thermal loading effect; long-term storage effect
- Identifier
- http://hdl.handle.net/1959.13/1471551
- Identifier
- uon:48697
- Rights
- This thesis is currently under embargo and will be available from 15.03.2024, Copyright 2023 Kaiwen Ouyang
- Language
- eng
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