This device rotated a vane embedded in the sediment at a constant 

 rate of rotation. A calibrated spring mounted in the apparatus 

 developed a torsional resistance to vane rotation that was semi- 

 empirically related to the undrained strength of the soil. 



The laboratory shear device, modified by NUC for shipboard 

 use, employed an AC electric motor to rotate the vane at a rate of 

 23 degrees per minute. The four-bladed vane had a 1.25-centimeter 

 diameter (D) and a 1.25-centimeter height (H) . The height-to-diameter 

 ratio (H/D) of the vane was, consequently, 1.0. During the strength 

 test, a graduated dial on top of the vane shear apparatus displayed 

 the degrees of torsional resistance corresponding to degrees of vane 

 deflection (Figure 1). 



The vane shear tests were conducted on various increments from 

 each sediment core. The number of vane tests per core varied according 

 to the amount of data necessary to establish a strength-versus-depth 

 correlation; however, five or more test series were usually performed 

 to define any strength-depth trends adequately. 



The vane shear test procedure involved the following sequence 

 of events: (1) the core length was sectioned, (2) the vane shear 

 tests were conducted on the core section, and (3) the tested section 

 was stored for later use. The Wykeham Farrance apparatus could only 

 embed the vane 4 centimeters below the soil surface; therefore, the 

 core length (liner with sample inside) was generally cut into 

 10-centimeter sections. 



The test procedure varied slightly for the upper 10 to 13 

 centimeters of core, since this material generally exhibited very 

 low shear strengths. To minimize the possibility of disturbance in 

 this zone, the top portion of the core was tested before sectioning. 

 The Wykeham Farrance apparatus had the capability of testing core 

 increments from to 1.0 meter long. When the length of the core 

 exceeded 1.0 meter, the core was sectioned at a lower depth (1.0 meter 

 from top) where the soil strength was considerably greater and, 

 consequently, the danger of disturbance was less. 



Each 10-centimeter sediment sample was tested at four depths. 

 The first and second depths were achieved by inserting the vane into 

 the top of the sectioned sample, while the third and fourth depths 

 were attained by inverting the sample and forcing the vane into 

 the sample's bottom. A distance of approximately one vane diameter 

 separated the individual tests (Figure 2). 



The vane shear tests at each depth consisted of original and 

 remolded strength determinations. The original tests were conducted 

 by rotating the vane in the undisturbed section of the sediment 

 sample. The value of maximum stress displayed on the graduated dial 

 corresponded to the "undisturbed" or original vane shear strength of 

 the soil. The remolded strength determination involved rotating the 

 vane several times to remold the soil in the failure zone, waiting 

 10 minutes, and again performing a stress-versus-strain determination. 

 The maximum stress represented the remolded strength of the material. 



