Another objective of DOSIST II was to obtain box core samples for 

 dynamic property testing. These have been transported to the University 

 of California, Berkeley, where they are currently being tested. 



FIELD OPERATIONS 



Vessel 



The USNS LYNCH (T-AGOR-7) was used as a support vessel during 

 DOSIST II. The ship is typical of the Navy's oceanographic vessels and 

 is adequately equipped with winches and U-frames for deploying conven- 

 tional oceanographic corers and other gear. 



Equipment 



In-place vane shear strength measurements were made with the ONR 

 vane tower developed by Dr. Adrian Richards of Lehigh University (Richards 

 et al. , 1972). The device is capable of inserting standard vanes (2x4 

 inches to 4 x 8 inches) (50 x 100 mm to 100 x 200 mm) to about 8 feet (2 m) 

 into the seafloor. The vane is rotated at about every foot (third of a 

 meter) of penetration, and the peak torque is used to calculate the in- 

 place undisturbed strength of the sediments. The sediment is remolded 

 by rapidly returning the vane to its original position. A second strength 

 measurement is made on the remolded sediment, and a sensitivity is 

 calculated (undisturbed strength divided by remolded strength) . The 

 vane is rotated at 90 deg/min (1.6 rad/min) , a relatively rapid rate. 

 This rate was chosen for operational convenience to reduce the time the 

 device needs to remain on the seafloor. 



The ONR device was used rather than CEL's DOTIPOS (Demars and 

 Taylor, 1971) because of its lighter weight and greater water depth 

 capabilities (15,000 feet versus 6,000 feet) (4,600 m versus 1,800 m) . 

 One of the major problems with the ONR device is that it is tall and can 

 be easily tipped over on the seafloor. The support vessel must remain 

 close to the tower, or large lateral forces will be exerted by the 

 tether line. Single-point deep sea anchoring was used to maintain the 

 ship's position during testing. 



Coring was conducted with a typical long piston corer and a spade- 

 type box corer. Cores were also taken with free-fall boomerang corers 

 and a NAVOCEANO hydroplastic corer. 



The long piston corer used is a Benthos Model 2450, a 2.6-inch-ID 

 (66— mm) triggered corer, weighing 2,700 pounds (1.2 Mg) . The piston is 

 self -deactivating. During corer penetration, the piston is held at the 

 sediment surface, and greater core recovery is produced. As the corer 

 is being withdrawn, the piston splits, with one section locking into 

 place at the top of the sediment and the other section being pulled to a 

 stop at the top of the corer. By allowing the piston to split in this 

 manner, additional material (''flow-in'') is not sucked into the bottom 

 of the corer during withdrawal. 



