Initial Penetration and Settlement of Concrete Blocks into Deep-Ocean Sediments
Two sets of concrete blocks of various shapes (a cube, a rectangular parallelepiped and a cylinder) of unit loads 3.78 kN/m2–7.31 kN/m2 (38.6–74.5 g/cm2) were placed on the floor of the San Diego Trough at a water depth of 1240 m to observe their short-term and long-term settlement behavior. Emplacement of the blocks and periodic observations of their settlement during a two-year period were accomplished using Lockheed’s submersible Deep Quest. In situ vane shear tests to a sediment depth of 122 cm and sediment cores varying in length from 93–120 cm also were obtained at the emplacement sites with Deep Quest’s vane shear device and coring unit.
From the in situ tests and laboratory tests on cores, engineering and mass physical properties of the sea-floor sediments were determined and used in conjunction with conventional soil mechanics methods to predict the settlement of the blocks at the two test sites. Settlement analyses included consideration of initial settlement, primary consolidation, secondary compression, and shear failure phenomena.
Results of settlement predictions approximate the total actual settlement observed. Differences between the predicted settlement and the observed settlement for the concrete blocks entering the sediment in an upright position varied from 0 to 2.4 cm with the maximum difference representing approximately 28% of the total settlement predicted. The amount of agreement between predicted and actual settlement values demonstrates the degree of applicability of terrestrial soil mechanics methods for analyzing finegrained saturated sea-floor sediments.
KeywordsConcrete Block Unit Load Initial Settlement Rectangular Block Total Settlement
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