Geotechnical and geophysical properties of deep marine fine-grained sediments recovered during the second Ulleung Basin Gas Hydrate expedition, East Sea, Korea

This study investigates the geotechnical and geophysical properties of minimally disturbed fine-grained marine sediments recovered during the second Ulleung Basin Gas Hydrate expedition (UBGH2), East Sea, Korea. Conventional laboratory geotechnical engineering test methods were used to characterize the sediments from a geotechnical engineering perspective. The sediments were mostly uncompacted and classified as highly plastic silty soils according to the Unified Soil Classification System (USCS); they exhibited high compressibility when subjected to an increase in effective stress (or a decrease in pore water pressure), low hydraulic conductivities, and low coefficient of consolidation (or pressure diffusion). It is expected that the application of a depressurization method for gas hydrate production at the investigated sites would cause a significant amount of settlement and compaction around the production hole. Because the shear wave velocity of gas hydrate-bearing sediments is much less sensitive to the stress state and is much higher than that of sediments without gas hydrates, it is possible to estimate the degree of hydrate saturation from shear wave velocity data measured in gas hydrate-bearing sediments. In addition, the prior presence of gas hydrates in the sediments was verified through a comparison of water content, compressibility, and electrical resistivity of the sediments.