The impact of THF hydrate veins on the consolidation behavior of fine-grained soils
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2021-01-26
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Abstract
Naturally occurring marine gas hydrates are ubiquitously found within sediments on continental slopes, where ongoing climate change or anthropogenic activities, such as hydrocarbon drilling and production, may dissociate the hydrates triggering slope instabilities. Large volumes of natural gas hydrate are contained within fine-grained marine sediments, observed as fracture filling veins, where these veins may hinder the sediment consolidation process resulting in weak, under-consolidated layers and possibly sea floor instability upon hydrate dissociation. Despite their potential impact, the behavior and properties of hydrates in fine-grained sediments remains poorly understood. To better understand the interaction between hydrate veins and consolidation, an experimental testing program was performed using cylindrical THF hydrate veins. Uni-axial compression tests, initially conducted on stand-alone THF hydrate specimens, indicated increasing specimen aspect ratio and reducing strain rate reduced compressive strength. Constant stress tests show the hydrate exhibits extensive plastic deformation as stresses approach failure conditions, with high aspect ratio specimens experiencing large out-of-plane deformations. Subsequent K0 consolidation tests on vein-bearing soil specimens, show considerable reduction in compressibility compared to those of the hydrate-free soils. Significant under consolidation of the soil occurs at high hydrate content and low to moderate confining stresses, although such effects are mitigated at higher confining stresses. These results indicate hydrate dissociation could lead to soil failure at low stress (i.e. shallow deltaic environments) and high hydrate content, and moderate to considerable volumetric deformation at high stresses (i.e. deeply buried sediments) and/or low hydrate content. Through this research, a better understanding of the impact of hydrate vein on the behavior of fine-grained soils has been achieved. This enables a more robust hypothesis to be developed for assessing the potential for submarine sea floor instabilities induced by hydrate dissociation through climate change. This may help evaluate the geohazard risk in marine environments and on coastal communities in these sensitive regions.
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Ma, B. (2021). The impact of THF hydrate veins on the consolidation behavior of fine-grained soils (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.