Geotechnical properties of the pacific seamount sediments measured by a gravity corer

Abstract

Geotechnical properties and distribution characteristics of the Pacific seamount sediments, which coexist with cobalt‐rich manganese deposits (crusts and nodules), are essential data for the design of a seafloor mining system for the deposits. Samples were cored by a large‐diameter gravity corer during the research vessel Hakurei‐maru No. 2 survey cruises on the Pacific seamounts in 1991 and 1992. Various distribution characteristics of the sediments were studied. Analysis of the core samples showed that the geotechnical properties of the sediments become very important, in view of the new findings of debris‐flow‐like resedimentation of the cobalt‐rich manganese deposits and large shallow‐buried deposits beneath the sediments. These new findings are also very significant in terms of reserve reassessment Fundamental geotechnical properties of the sediments, such as size distribution, solid density, bulk density, water content, coefficient of internal friction, and cohesion are presented. Based on these data, their effects on the mining system design are also presented.