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- All Subjects: Biogenic Gas
- Creators: Kavazanjian, Edward
Description
One of the most economical and viable methods of soil improvement is dynamic compaction. It is a simple process that uses the potential energy of a weight (8 tonne to 36 tonne) dropped from a height of about 1 m to 30 m, depending on the project requirement, on to the soil to be compacted hence densifying it. However, dynamic compaction can only be applied on soil deposits where the degree of saturation is low and the permeability of the soil mass is high to allow for good drainage. Using dynamic compaction on saturated soil is unsuitable because upon application of the energy, a part of the energy is transferred to the pore water. The technique also does not work very well on soils having a large content of fines because of the absence of good drainage. The current research aims to develop a new technology using biogenic gas production to desaturate saturated soils and extend the use of dynamic compaction as a ground improvement technique to saturated soils with higher fines content. To evaluate the feasibility of this technology an experimental program has been performed. Soil columns with varying soil types have been saturated with substrate solution, resulting in the formation of nitrogen gas and the change in soils volume and saturation have been recorded. Cyclic triaxial tests have been performed to evaluate the change in volume and saturation under elevated pressure conditions and evaluate the response of the desaturated soil specimens to dynamic loading. The experimental results showed that soil specimens treated with MIDP under low confinement conditions undergo substantial volume expansion. The amount of expansion is seen to be a factor of their pore size, which is directly related to their grain size. The smaller the grain size, smaller is the pore size and hence greater the volume expansion. Under higher confining pressure conditions, the expansion during gas formation is suppressed. However, no conclusive result about the effect of the desaturation of the soil using biogenic gas on its compactibility could be obtained from the cyclic triaxial tests.
ContributorsBorah, Devajani (Author) / van Paassen, Leon A. (Thesis advisor) / Kavazanjian, Edward (Committee member) / Zapata, Claudia E. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Microbially induced desaturation (MID) via denitrification is an emerging ground improvement technique to mitigate liquefaction by stimulating the metabolic processes of native bacteria to produce biogas, biominerals and biomass. The production of biogenic gas gradually lowers the degree of saturation of treated soils, thereby dampening the pore pressure response to cyclic loading. However, the production of these metabolic products also alters the hydraulic and mechanical properties of the soil. A series of four tank tests simulating two-dimensional plane strain conditions were performed to evaluate the effectiveness of MID and the resulting changes to the hydraulic properties of the soils. Previous studies have demonstrated the mechanical response for treated homogenous granular soils at the bench scale via vertical injection methods. However, limited knowledge is available on the impact of partial desaturation on the hydraulic properties of the soil, particularly in stratified formations. Treating larger granular soil specimens via lateral injection methods is important for the up-scaling and future commercialization of the process as it may affect injection strategies, and the distribution of substrates and metabolic products. Tank tests were performed on a layered natural soil sediment collected from Richmond, British Columbia, Canada, as well as layered and unlayered laboratory grade Ottawa sands of different grain size distributions. The results demonstrated the effectiveness of treatment upon macro-scale soil properties, and showed how gas formation, migration and entrapment, and resulting degree of desaturation and hydraulic conductivity are affected by micro and macro-stratifications in granular soils.
ContributorsStallings Young, Elizabeth Grace (Author) / Zapata, Claudia E (Thesis advisor) / van Paassen, Leon A (Thesis advisor) / Kavazanjian, Edward (Committee member) / Arizona State University (Publisher)
Created2021