INTRODUCTION 



Subject and Purpose of Report 



This report describes the development and the evaluation by the 

 Naval Civil Engineering Laboratory (NCEL) of a seafloor soil testing 

 device capable of performing vane shear and static cone penetrometer 

 tests to a depth of 10 feet into the seafloor. Data are presented 

 from tests with this equipment at two seafloor locations. The program 

 was sponsored by the Naval Facilities Engineering Command. The overall 

 objective of this program was the development of a device with associated 

 test procedures with which the in-situ strength characteristics of 

 seafloor sediments may be determined to a sediment depth of 10 feet 

 at water depths to 6,000 feet. The device will be employed to generate 

 data which will enhance the Navy's ability to design and construct 

 foundations for seafloor structures. 



Background 



The design of foundations for Naval seafloor installations 

 requires detailed information on the strength properties of seafloor 

 sediments as they exist in situ. Present information for seafloor 

 foundations has come from the laboratory analysis of marine sediment 

 cores. The present sampling techniques, however, are known to disturb 

 the soil and provide a poor engineering sample for a sophisticated 

 laboratory analysis. In addition, most laboratory analyses have been 

 performed by geologists and oceanographers with little regard for the 

 sediment's foundation-supporting properties. Consequently, seafloor 

 foundations have been designed with a high factor of safety, a procedure 

 which is unnecessarily expensive. Sometimes the intended high factor 

 of safety may, in actuality, be dangerously low because of unknown or 

 unanticipated conditions. 



For more precisely designed seafloor foundations, improved techniques 

 should be developed to obtain more accurate design data. Two alterna- 

 tives are possible: (1) develop improved soil sampling equipment and 

 laboratory test techniques or (2) develop equipment to determine the 

 engineering strength properties of sediments in situ. It is apparent 

 that neither of these approaches is sufficient by itself for all 

 design applications. However, information which is obtained in situ 

 is valuable for foundation design, and it may be used to evaluate the 

 accuracy of laboratory data derived from the analysis of core samples, 

 and vice versa. This program is concerned only with the development 

 of an in-situ test device capable of obtaining the vane shear strength 



