Development of In-Situ Measuring Apparatus of Geotechnical Elements of Sea Floor (IMAGES)
Authors: Tsurusaki K. , Itoh F. , Yamazaki T. 
Published: October 2008

The effort of the research and development of manganese nodule mining system from deep ocean floor has been concentrated in several countries this decade. Among many sub-systems of the mining system it is said that the development of collector system which harvests manganese nodule on the sea floor involves most difficult problems. The engineering properties of deep sea floor is one of the most important factors to develop efficient and sage collector system.

The authors designed and fabricated in-situ measuring apparatus of geotechnical elements of sea-floor (IMAGES) which measured automatically. It is lowered to sea floor from surface ship with wire rope. After reaching on sea floor it starts vane test, cone test, and bearing capacity test. The data measured are recorded on the magnetic tape contained in a pressure vessel.

After laboratory and shallow water tests IMAGES was tested in south Central Pacific maganese nodule province. But some units driven by underwater motor did not work enough on the sea floor and very limited data were collected. Presently many experiments to clarify the cause of this unexpected results are being carried out. After getting the answers we will rearrange the IMAGES and try to collect data of in-site deep sea floor engineering properties in Pacific again.

INTRODUCTION

Research and development for mining system of mining manganese nodule which are distributed on the 4000?6000m deep sea floor has started in Japan recently as a national research program. This mining system consists of several sub-systems, such as collecting, nodule lifting, machinery handling, controlling, and total system. Among these sub-systems it is said the research and development of collecting systems involves most difficult problems. To understand the behavior of the collector on the sea floor the bearing capacity, settlement properties, traffic ability, and etc. of the deep sea sediments should be known (Richards, 1981). The drag resistance of machinery elements in the deep sea mud tend to be affected by the adhesiveness of mud very much (Noorany, 1983). Thus in order to develop collector system which can collect nodules efficiently and safely it is important to clarify the geotechnical properties of deep sea floor.

As deep sea mud showes high water content, low strength, and very high sensitivity it is very difficult to know the accurate value of geotechnical properties form the measurement son specimen sampled from sea floor even measured on board just after recovering.

The authors have planned to develop in-situ automatic measuring apparatus for geotechnical properties of deep sea floor which are required for the development of collector system. This in-situ measuring apparatus of geotechnical elements of sea-floor (IMAGES) has been designed to collect data of engineering properties, such as bearing capacity, settlement properties, cohesiveness, and etc., through the plate bearing test, vane shearing test, cone penetrating test, and blades dragging test and to collect piston core sample for clarify other fundamental properties in laboratory on land.