Geotechnical properties of deep-sea sediments which have important roles for design of manganese nodule miner and mining system are presented. They are water content, vane shear strength, sensitivity, cone penetration resistance, cohesion, friction angle, and dynamic moduli of elasticity and viscosity. The interactions with the miner are examined. Efforts for in-situ measurements of the properties are introduced.
Manganese nodules are the first recognized deep-sea mineral resources (Mero, 1965; Cronan, 1980) and are currently again interested in as future metal sources for cobalt, nickel, copper, and manganese because of recent increases in demand for these metals (Yamazaki and Park, 2005). Through the R&Ds, the hydraulic dredge with either a towed or self-propelled miner was selected by many as their mining systems for their R&D targets. Relatively higher reliability and longer operation time for the towed and relatively higher controllability of the miner pass for the self-propelled can be considered main advantages of each miner. For the design of the towed and self-propelled miners for manganese nodules, some of the most important factors are the static and dynamic geotechnical properties of deep-sea sediment layer in manganese nodule distribution area (Richards and Chaney, 1981). Many data have been collected from the measurements against the samples recovered on board survey vessels with core samplers by the authors. The example results are introduced in this article. However, less information has been available from the insitu measurements. Because of high sensitivity characteristics against mechanical disturbance on the deep-sea sediment layer, it is necessary to compare the data between obtained from samples and measured in-situ. The first trial of the in-situ measurement on the geotechnical properties of deep-sea sediment layer by the authors was the development of IMAGES (In-situ Measurement Apparatus of Geotechnical Elements of Seafloor) in 1983 (Tsurusaki et al., 1984).