and rotational displacement of the vane. A series of traces such as that shown 

 in the facsimile will comprise all the test data for one location to a 10-foot 

 depth in the sediment. 



The collected field data are reduced on the basis of the usual 

 assumption 17 of the shear stress distribution around a vane. A typical peak- 

 shear-stress-versus-sediment-depth plot is shown in Figure 17, which represents 

 the strength profile at a particular location in the waters off the Southern Calif- 

 ornia coast. 



This vane shear device is considered primarily a tool for performing 

 research on seafloor sediments for the purpose of determining the relation- 

 ship between laboratory-measured values and in-situ-measured values of 

 strength. 



In-Situ Cone Penetrometer Device 



The in-situ cone penetrometer device 31 is used also with the DOTIPOS 

 to conduct static cone penetration tests in sediments. The depth capabilities 

 of this device are the same as for the vane shear device. The conversion from 

 the vane shear mode to the penetrometer mode is accomplished simply by 

 replacing the vane with the cone penetrometer. The cone being used has a 

 90-degree apex angle, a diameter of 2.256 inches (4 square inches projected 

 area), and a height of 1 .625 inches. 



In testing with this device, the cone is pushed into the sediment at a 

 constant displacement rate of 10 inches per minute. During penetration, the 

 force to drive the cone into the sediment and the depth of penetration are 

 continuously recorded on deck through the same system as for the vane shear 

 device. An example of the type of data obtained from reduction of the records 

 is shown in Figure 18, which is a plot of penetration resistance versus depth in 

 the sediment. 



The static cone penetrometer test results can be related to the peak 

 shearing strength of the sediments. This relationship has to be evaluated for 

 marine sediments before the full meaning of the penetrometer test values 

 can be understood and utilized. 



The penetrometer test has advantages over the vane shear test in 

 determining sediment strength properties. The penetrometer has the capa- 

 bility of performing tests more rapidly than the vane shear device. It also 

 produces a continuous profile of strength with depth rather than at discrete 

 depths as obtained by the vane shear. The vane shear, however, has the 

 capability of testing remolded sediments, the strengths of which will be a 

 controlling factor for many ocean construction projects and operations. 



30 



