- Title
- Multi-scale study of the hydro-mechanical behaviour of Maryland clay
- Creator
- Yuan, Shengyang
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The damage caused every year to buildings and infrastructure by expansive soils, also called swelling soils, is very high (e.g. Chen, 1975; Nelson et al., 2015). It is crucial to adequately characterize the hydro-mechanical behaviour of expansive soils in order to better assess the long-term durability of structures that are built against such soils. Such task is not trivial because previous research has revealed complex hydro-mechanical couplings that are possibly stress path dependent. In addition, the scientific literature contains experimental evidence highlighting the importance to consider the soil microstructure and its possible evolution, when characterizing the hydro-mechanical behaviour of expansive soils. To date, comprehensive multi-scale hydro-mechanical studies on expansive soils are still scarce and no such characterization was undertaken for Maryland clay, a local natural expansive soil. This thesis presents the outcomes of series of swelling tests under a range of boundary conditions (constant stress, constant volume, and constant stiffness) and permeability tests. Since hydration of an expansive soil leads to significant microstructural changes, comprehensive microstructural analyses (mercury intrusion porosimetry and scanning electron microscope imaging) were conducted to complement all swelling and permeability tests and to better understand of the soil behaviour. The thesis presents two experimental developments before discussing aspects of the fundamental hydro-mechanical behaviour of Maryland Clay. The experimental developments pertain to: ; The comprehensive calibration of the osmotic technique when used with polyethersulfon membranes (PES). The calibration accounts for the effect of polyethylene glycol (PEG) concentration, PEG molecular weight and, most importantly, temperature. This comprehensive calibration shows that as temperature increases: (1) the applied suction reduces, which is contrary to van’t Hoff equation and the virial model and (2) the suction applied depends on the PEG molecular weight, which is not the case at 20°C. ; The development and validation of a new sensor to evaluate the concentration of PEG solution. The sensor is based on the idea of laser absorbance and allows in situ and automated measurement of PEG concentration. A linear correlation was obtained between PEG concentration and absorbance. Unfortunately, although developed and validated, the sensor could not be used in daily testing for a matter of robustness. More research is needed to create a more robust and improve accuracy. The findings on the fundamental hydro-mechanical behaviour pertain to: ; A multi scale study of the swelling response of Maryland clay with a focus on primary and secondary swelling. This study provides insight onto the microstructural evolution of compacted Maryland clay specimen upon swelling. ; A study on the effect of boundary conditions on the swelling response of compacted Maryland clay. The locus of final swollen states (noted LFS), defined in the “swelling pressure-swelling strain” plane was established and was found to be independent of stress-volume path along monotonic wetting paths. Micro structural data showed that specimens reaching the same point on the LFS undergo similar extent of micro structural changes. ; The evolution of microstructure during permeability tests and its effect on the saturated permeability of Maryland Clay. Different soil structures were tested and two different permeability testing methods were employed. The saturated permeability was correlated to various microstructural descriptors and the results highlight a strong tortuosity effect. ; A discussion, supported by extensive experimental data, on the identification of a boundary to partition micro and macro pores from pore size distribution obtained from Mercury Intrusion Porosimetry. The discussion presents and compares the most common criteria available in the literature to select a boundary. The paper then focuses on some of the aspects of soil behaviour that ought to be considered when selecting a boundary.
- Subject
- expansive soil; microstructure; swelling; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1354670
- Identifier
- uon:31324
- Rights
- Copyright 2017 Shengyang Yuan
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 14 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 52 KB | Adobe Acrobat PDF | View Details Download |