semisolids, the ground bearing capacity will be low. Second, while only 
sufficient traction is needed to allow slow but positive movement, with 
low-shear-strength soils even this may be difficult to develop. Third, cur- 
rent concepts call for working from an oriented, fixed platform which would 
be periodically moved—thus the need for traction. Once positioned, the plat- 
form must remain stationary during the work period. Low-shear-strength, 
saturated soils are essentially plastic and appear to have low viscosity under 
sustained loading. Even small reaction forces from the work tools may be 
expected to cause some movement of the platform. 
Trafficability of the Ocean Floor 
In order to support a load and develop traction on the ocean floor, 
it is necessary to determine the physical characteristics and eventually the 
load-supporting ability of the materials that make up the ocean bottom. 
These parameters must then be related to the characteristics of the specific 
load-carrying devices intended for use. 
As the earthmoving or construction equipment must be able to work 
anywhere on the ocean bottom, it must be designed for operation on soil with 
the lowest bearing and shear strength known to exist. Because there will be 
no problem on rock or hard-packed sand and gravel bottoms, only the softer 
sediments need be considered here. 
There are six principal types of sediments found on the ocean bottoms 
of the world (Keller, 1968). They are: (1) fluvial-marine (sand-silt) representing 
the coarser fraction (larger than 0.016 mm); (2) fluvial-marine (silt-clay) the 
finer fraction (smaller than 0.016 mm) of material derived from terrestrial 
drainage; (3) red clay, a term applied to inorganic pelagic clays which vary 
considerably in color but are usually chocolate brown; (4) calcareous 00ze, 
used here to identify sediment composed of at least 30% calcium carbonate 
in the form of skeletal material from various planktonic animals and plants. 
Globigerina oozes are included in this sediment type; (5) calcareous sand and 
silt consisting of shell fragments and coralline debris of sand and silt-size 
particles; (6) siliceous oozes, deposits containing 30% or more of siliceous 
skeletal material derived from either diatoms or radiolarians. 
These sediments cover approximately 75% of the ocean bottom. 
Calcareous oozes cover 67% in the Atlantic, 36% in the Pacific, and 54% in 
the Indian Oceans; siliceous oozes cover 7% in the Atlantic, 15% in the Pacific 
and 20% in the Indian Oceans; and red clay covers 25% in the Atlantic, 49% 
in the Pacific and 25% in the Indian Oceans (Sverdrup, Johnson and Fleming, 
1942). 
Generally speaking, the red clays are found at depths greater than 
18,000 feet and the oozes between 6,000 and 18,000 feet, according to 
Marmer (1930). 
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