Marine geotechnique

Marine geotechnique is the study of the physical and physicochemical properties of seafloor deposits. Geotechnical ocean engineering is the study of the design, analysis, and modelling techniques used in the construction of seabed facilities. Seafloor sediments are a multiphase system, mainly comprised of solid–pore water–gas (usually methane, often absent) mixtures. The response of this multiphase system to applied static and dynamic loads is usually inferred indirectly by measuring various physical, chemical, biologic, and acoustic properties of the sediments, and by applying principles of soil mechanics theory to the subsea environment. Direct in situ measurements by oceanbottom devices and/or sampling by manned or unmanned submersibles is rarely done in deepwater (>200-m) settings because of the high cost of such endeavors.

During the 1970s geotechnical ocean engineering studies concentrated on the continental shelf in water depths of <200 m, in contrast with most of the marine geotechnique work that has been done on sediments sampled from the deep sea. Much of the interest in marine geotechnique has evolved from the Deep Sea Drilling Project (DSDP) and its successor, the Ocean Drilling Program (ODP), as well as from interest in deep-sea ocean mining, laying of transoceanic power and communications cables, and environmental impact studies of hazardous waste disposal in deep-sea sites. For slopestability investigations involving either total or effective stress methods of analysis, the key parameters to be measured are bulk density, shear strength, excess pore pressure, and cyclic shear strength (i.e., number of cycles needed to failure; Richards, 1984).