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The effect of biological exudates on the mechanical properties of granular soil

Al-Awad, Khabeer 2018. The effect of biological exudates on the mechanical properties of granular soil. PhD Thesis, Cardiff University.
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Abstract

This study explores how biological processes can be used to enhance the geotechnical characteristics (shear and permeability data) of soils. In particular, the creative use of microbial substances to efficiently improve the mechanical properties (shear parameters) of soils is studied. The research studies give an excellent opportunity for understanding the principles of biological processes in geotechnical engineering development. Specifically, biofilm behaviour is a part of the interactions between geotechnical engineering and the biological process of microorganism growth. The main research questions of this study are how biofilm affects the shear parameters of granular soil under low normal stresses. To that end, this study concerns experimental work to explore the effect of accumulated bacterial biopolymer (biofilm) on the shear response of well-graded silica sand. A comparison is achieved between biotreated samples with un-biotreated samples as well as comparing with clean dry and saturated samples under the various testing conditions are considered. To address the objectives of this study, experimental work was conducted using an adapted direct shear test procedure that enables proper tests to investigate the impact of biofilm on the shear strength in a saturated condition. Moreover, these tests were performed at a displacement rate of 0.5 mm/min, and at various normal stresses (1.0, 4.1, 8.89, 16.2, and 25.0 kPa). The soil samples (defined as biotreated samples) were prepared to encourage biofilm growth and the production of exopolymeric substances (EPS) by supplying a glucose rich nutrient. The control samples produced by delivery of a glucose free nutrient (defined as standard samples). All samples were prepared and tested in triplicate. Furthermore, this study VI explain the influence of the biofilm on a poorly graded silica sand and a sea sand. The effect of various testing rates on the biotreated and standard sample was also investigated. The important finding of this study was that the potential impact of biofilm on densification on preloading biotreated sand samples. The growth of biofilm increases the ability of samples to densify under applied normal stress during incubation period compared with control samples. All biotreated samples show larger peak stress than the shear stresses of standard specimens. These differences may be because of the differences of loss on ignition content in both sample types. A biotreated sample contains higher biomass than that in the standard samples. The amount of formed biofilm in the biotreated poorly-graded silica sand and sea sand was significantly more than in the well-graded silica sand. This biofilm has had a similar effect on peak stress of both the well and poorly graded.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Biofilm; Biological stabilisation; Biological Exudates; Bioaggrigate; Extracellular Polysaccharide Substances; Exudates.
Date of First Compliant Deposit: 10 April 2018
Last Modified: 10 Apr 2018 09:03
URI: http://orca-mwe.cf.ac.uk/id/eprint/110599

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