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Title: The distribution and assessment of sulfur-species in geological materials : implications for geoenvironmental engineering
Author: St. John, Thomas William
ISNI:       0000 0004 5914 5677
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Sulfur-species in geological materials have detrimental consequences for geoenvirormental engineering. The research considers aspects of sampling, testing and assessment that were identified as in need of further investigation. Field and laboratory studies show that the distribution of sulfur-species with depth below ground level can be divided into three zones: an upper sulfate leached zone, an intermediate zone with sulfate-horizons and a lower sulfate-poor, sulfide-rich zone. Based on this zonation, a targeted sampling strategy for sulfur-species is presented and permits application of existing classifications for aggressive ground. Petrographic studies of mudrock aggregates reveal the variations in sulfur-species morphology. It is shown that both framboidal and euhedral pyrite can oxidise extensively and that expansion due to gypsum growth may comprise several stages. Dehydration of hydrous sulfate minerals during sample drying was found to be insignificant for typical sulfur-species concentrations. Where high levels of accuracy are required, air-drying (<40ºC) is suitable, however vacuum drying may be required to remove all water from clay soils. The UK gravimetric method for acid-soluble sulfate determination was found to suffer from numerous error sources, with ±0.1% S042- error possible. Use of ICP-OES/AES to quantify sulfate in an acid-extract improved accuracy by an order of magnitude, to an acceptable level for sulfate contents around the tolerance for geo-materials. ICP-OES/AES is recommended as the standard method, with gravimetry to be used only if the sample mass is increased ten-fold. A review of the limitations associated with derived chemical terms such as equivalent pyrite shows that each term relies heavily on assumptions that may not be valid under certain conditions, particularly in the presence of insoluble sulfates and organic sulfur. The geoenvirorunental implications of the research findings are discussed in the context of various ground engineering scenarios and best-practice recommendations are made.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available