Influence of vertical cylindrical tetrahydrofuran hydrate veins on fine-grained soil behaviour

Abstract

Over the last 10 years, marine gas hydrate drilling expeditions utilizing advances in pressure coring techniques and imaging have routinely encountered gas hydrates residing in fine-grained sediments. The hydrate typically occurs as fracture-filling, near vertical, veins that displace the sediment, potentially leading to increased sediment strength that may prevent normal consolidation of the sediment thus leading to underconsolidation. Destabilization of this hydrate, through climate change or human activity on the seafloor, may cause dramatic loss of strength of the sediment and pose a significant geohazard. To assess the impact of hydrate veins on sediment behaviour, this paper reports on a series of consolidated (CU) and unconsolidated undrained (UU) triaxial tests carried out on fine-grained soil specimens hosting simplified, vertical, cylindrical tetrahydrofuran (THF) hydrate veins of varying diameters. The results show that increasing hydrate vein diameter significantly increases strength and stiffness, including the development of post-peak strain-softening. The mode of failure of the hydrate veins influenced the specimen strength, but did not affect the specimen stiffness. Hydrate dissolution during CU tests prevented quantitative comparison with UU tests. However, CU test results on the soil specimens containing the largest hydrate vein suggest that increasing lateral confining stresses increase the sediment strength.