In an effort to evaluate testing substitutes for deep-ocean sediment, laboratory investigations have been made into the lateral movement of tools or rods through submerged, low shear strength clays and the sliding of plates over the surface of these weak clays. This work resulted in predictive relationships for drag forces acting on tools and the determination that drag forces acting on plates are characterized primarily by Coulomb friction with a relatively low friction coefficient.
While much information has been published on the interaction of various machine or mechanical elements or systems with terrestrial or land-type soils, only a limited amount has been published on such interactions in near shore or terrigenous sediments, and virtually none has been published on the interaction of mechanical elements with the siliceous clays typical of the deep-ocean manganese nodule areas [l]. The most obvious means of obtaining such information for deep-sea sediments would be to perform detailed in-situ testing; however, for a program of any significance, in-situ testing would be at least prohibitively expensive if not beyond the present state-of-the-art in deep-ocean work.
The alternative to in-situ testing is, of course laboratory testing. Ideally, lab testing would involve the execution of a program in which the interaction of mechanical elements with deep-ocean sediment samples would be studied. However, the high cost, relative scarcity, and small size of the available undisturbed deep-sea sediment samples, coupled with the complex nature of the sediment, would limit such a testing program severely.
An obvious means for bypassing this sediment availability problem would be to:
develop a substitute testing medium which would duplicate the characteristics of deep-sea sediment relative to interactions of interest; or
develop an analytical model to extend results of interaction testing in a medium different from deep-sea sediment to cover interactions in deep-sea sediments.
The objective of the efforts described in this paper was to determine the feasibility of developing either a substitute sediment or an analytical system which would permit the testing of future mechanical developments in the laboratory. The aforementioned scarcity of deep-sea sediment samples necessitated a different approach to the problem than might normally be taken. The initial efforts in this study were directed towards the selection of substitute sediments on the basis of similarity of engineering properties to deep-sea sediments. A variety of soils and sediments were considered with an illite and several Kaolinite-Bentonite mixtures finally being selected. These sediments were then subjected to a series of tests designed to simulate two classes or types of mechanical element/sediment interaction thought to be common to the operation of most deep-sea mining equipment. These two classes of interactions were:
sediment displacement types of interactions such as shallow lateral penetration or plowing of the sediment by tools or blades; and
the shearing or sliding type of interaction involved in the movement of a flat plate or smooth surface over the sediment.
