Near surface sea floor soils were obtained, with a sampler attached to the tracked underwater vehicle RUM, from eight regions off the coast of Southern California. The soils represented the continental shelf deposits as well as deep sea floor sediments. The geotechnical properties of these soils, including grain-size distribution, index properties, strength and compressibility, were determined.
This paper describes the geotechnical properties of 28 sediment cores from eight areas on the floor of the Pacific Ocean off the coast of Southern California. The water depths ranged from 46 m. (25 fathoms) to 1199 m. (655 fathoms). The cores were taken by a 7.30 cm. in diameter, 56 cm. long sampler attached to the manipulator arm of the RUM (Remote Underwater Manipulator), a research vehicle of the Marine Physical Laboratory of the Scripps Institution of Oceanography, University of California. The sediment cores were stored in a 50C refrigerator and were tested at the Soil Mechanics Laboratory of San Diego State University, San Diego.
The RUM (Fig. 1), is an unmanned tracked vehicle developed for sea floor explorations in water depths up to 2440 m. (8000 ft.) deep. An umbilical cable connects RUM with a surface support platform ORB (Oceanographic Research Buoy) which provides the power and controls RUM. Various features of the RUM/ORB system are shown in Fig. 2. RUM has been instrumented for a number of underwater measurements (2). Among these are a remotely controlled sediment corer (Fig. 3), in-situ vane shear device and a cone penetrometer (3,4) which have been used in waters as deep as 1830 m. (6000 ft.).
The RUM/ORB system was deployed at eight different areas off the coast of Southern California during the months of January, February, March, May and June, 1972. The soil samples described in this paper were obtained from the upper 60 cm. of the sea-floor sediments. The eight areas explored were: La Jolla Canyon, La Jolla Fan, the continental shelf off Bird Rock, the edge of the continental slope west of Bird Rock, the continental shelf off the coast of Point Lorna, the edge of the continental slope west of Point Lorna coast, top of the Coronado escarpment, and the floor of the San Diego Trough.
The index properties of the samples are summarized in Table 1. The grain size distribution was determined from hydrometer test. The specific gravity of solids was measured by the pycnometer method, and the plasticity indices (liquid limit, plastic limit and plasticity index) were determined from Atterbert Limit tests. The liquidity index, in Table 1 is defined by the following equation.
