Geotechnical properties of northern Bering Sea sediment

Abstract

The physical properties of sediments taken from the northern Bering Sea (Norton Sound area) have been determined in order to evaluate their impact on recently identified possible geologic hazards in the area. Standard identification tests (water content, Atterberg limits, grain size, specific gravity and density) as well as shear strength and compressional testing were conducted either on board the ship or in the laboratory. The greatest thickness of Holocene sediment occurs in Norton Sound and is located in the Yukon prodelta region. This sediment is predominantly sand-silt that appears to be highly overconsolidated. The observed overconsolidation, in view of the shallow water depths throughout the region, appears to be related to storm wave surges that severely affect the bottom. Indications of gas-charged sediment have been found in several areas of Norton Sound. Gas-charged sediment has been responsible for failures of structures in other resource development areas and generally will tend to reduce the strength characteristics of the sediment, as a result of generation of high excess pore pressures. The overall stability of the bottom sediment could be seriously affected, particularly if excess pore pressures are generated by storm wave activity in regions of gas-charged sediment. Because of the difficulty experienced with sampling intact gas-charged sediments, in-place testing equipment is considered necessary for future work to more accurately assess the impact and extent of the gas charging. Several cores that were taken for this study penetrated into peaty muds. The overall extent of the peaty muds and stability characteristics are not well known at this time, but should be assessed in future work with coring devices capable of greater penetration depths.