This report will consider only unaided breakout of partially embedded 

 objects from cohesive seafloor soils. Breakout of embedment anchors^' ^ and 

 aided breakout of partially embedded objects-^-^ are considered elsewhere. 

 The results presented in this report are intended to serve as a guide to deter- 

 mine whether aiding is necessary, and, if not, the effort required for unaided 

 breakout. 



Background 



Breakout Testing at NCEL. After the loss of the USS Thresher, the 

 Naval Civil Engineering Laboratory (NCEL) initiated a 3-year program to study 

 breakout forces as a part of the Deep Submergence Systems Project (DSSP). 

 The specific objective of this program was to develop procedures for predict- 

 ing forces required to rescue or salvage sunken vessels such as the Thresher. 

 Unaided breakout of partially embedded objects from cohesive soils was the 

 main area of investigation. During the first year of this program, large-scale 

 field tests were conducted at the Naval Ordnance Test Station, Seal Beach, 

 ocean bottom simulation facility. Various objects, several shaped somewhat 

 like submarines, were placed in a highly heterogeneous clayey silt obtained 

 from nearby borrow areas. The objects were subsequently broken out, and 

 the time and force required were measured. An unsuccessful attempt was 

 made to correlate the experimental results through use of fluid mechanics 

 principles. A major problem involved in making any correlation of these data 

 was found to be the heterogeneity of the soil. It was impossible to assign any 

 consistent series of parameters to the soil being tested. The value of these ini- 

 tial tests was the opportunity they provided to view the breakout mechanism 

 directly. The tests also provided an opportunity to study the effects of lifting 

 an object from one end rather than from its center of mass. This was apparently 

 effective in reducing the required breakout force. ^ 



During the second year of the DSSP breakout test program, field tests 

 were conducted in about 30 feet of water in San Francisco Bay near the San 

 Francisco Naval Shipyard at Hunters Point. Objects were partially embedded 

 in the bottom soil and then lifted free. The required breakout forces were 

 provided by a counterweight mounted on a moored barge. Each test consisted 

 of first applying a specified uplift force to a partially embedded object and then 

 measuring the upward displacement of the object as a function of time. Some 

 of the soil properties were obtained from laboratory tests on core samples and 

 also from in-situ shear tests conducted with a diver-held vane device. An 

 empirical equation which related the soil shearing characteristics to the 

 breakout force— time behavior was constructed.^ 



