OPTIMAL GEOTECHNICAL PROPERTIES OF DEEP-SEA SEDIMENT FOR THE DESIGN OF MN-NODULE MINER IN THE C-C ZONE OF THE NORTHEAST EQUATORIAL PACIFIC

Deep-sea surface sediments were sampled from 1997 to 2002 in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific. Samples were analyzed for geotechnical properties to provide background information for the design of manganese nodule miner. The sediments were classified in terms of the maneuverablility of the miner and potential environmental impacts arising from mining activities based on the measured properties (i.e. shear strength, index properties). The result shows that the middle part of the study area covered with coarse siliceous sediments is more favorable to the commercial mining than the northern part of the study area covered with pelagic red clay. Especially, area B2 in the middle part is considered to be the best mining site because this site shows the highest abundance of manganese nodules. Moreover, the sediments of this site consist of normally- to over-consolidated (types B, C, D) coarse siliceous sediments, which are appropriate for effective miner movement and less environmental impacts. Based on all data, suggested optimal shear-strength values, known as a practical guideline for movements of a manganese nodule miner, are 6.0 kPa at 10 cm and 7.0 kPa at 40 cm below the seabed at this site.