Quite often the only information on the engineering properties of the 

 bottom sediment which is available or economically obtainable is from a few 

 cores collected in the vicinity of the operations site. Thus, techniques for 

 predicting the short-term and long-term settlements which can be expected 

 when an object is emplaced, based on the results of conventional sediment 

 core analyses, would be very useful in many situations. This report addresses 

 itself primarily to the problem of predicting short-term settlement for small 

 spread footings using the results of in-situ tests with NCEL's Plate Bearing 

 Device and laboratory tests on cores recovered from the in-situ test sites. 



Background 



For several years NCEL has been developing test equipment, performing 

 research, and accumulating data on the engineering properties of marine sedi- 

 ments and their response to foundation loads. Under this program a device for 

 performing in-situ plate bearing tests on the seafloor was developed and tested. 

 The basic characteristics of this equipment and the results of the first two series 

 of tests have been previously reported.^ At the time of this initial report the 

 equipment was still in the developmental stages and had only been operated in 

 a maximum water depth of 150 feet. Improvements have subsequently been 

 made to both the mechanical and instrumentation systems, and tests have been 

 performed in sediments located in water depths of over 6,000 feet. The reason 

 for developing the plate bearing device was to provide a method for obtaining 

 the bearing pressure— settlement response of the seafloor to loads imposed on 

 small spread footings. Information from this test provides a basis for predicting 

 the immediate settlement which occurs when a structure is placed on a spread 

 foundation located at the sediment— water interface. Reliable information of 

 this type is not presently obtainable for seafloor sediments from the analysis 

 of laboratory tests on core specimens. It was anticipated that it would even- 

 tually be possible to relate the bearing pressure— settlement response of a 

 foundation to a laboratory-measured property such as vane shearing strength 

 if sufficient data were obtained both in situ and in the laboratory. 



Approach and Scope 



NCEL's approach to the problem of predicting the immediate settlement 

 of spread footings on the seafloor has been to develop a test device capable of 

 forcing various sizes and shapes of footings into the seafloor at a controlled 

 rate and to measure the bearing pressure— settlement response resulting from 

 tests using this device. In addition sediment cores were obtained at the test 

 sites and analyzed in the laboratory. Schemes have been developed and are 



