and static cone penetrometer resistance of seafloor soils. Future efforts 

 will be concerned with the Improvement of soil sampling equipment and 

 laboratory test techniques that complement in-situ test data. The 

 overall program will provide the Navy Engineer with much greater test 

 flexibility, and with the ability to measure many different soil 

 responses and thereby increase design efficiency. 



The vane shear and static cone penetrometer test devices were 

 chosen because of their reliability, simplicity and widespread popularity 

 for testing saturated terrestrial soils. The devices have been used 

 successfully on terrestrial soils to determine the undrained shear 

 strength of soft saturated soils. For structures founded on soft 

 saturated soils, the initial loading conditions are critical; the 

 effective soil stress due to high excess pore pressures is at a minimum, 

 and the potential for shear failure is the greatest. The vane shear 

 tool and static cone penetrometer will determine shear strengths under 

 conditions duplicating initial foundation loads. Seafloor soils are 

 expected to behave in many ways similar to soft saturated terrestrial 

 soils; therefore, the vane shear and static cone penetrometer should 

 be equally applicable for determining the critical support load. 



Terrestrial field vane shear tests consist of forcing a four- 

 bladed vane into the soil, usually from the bottom of a bore hole, or 

 hand-driven from the surface with a sledge hammer. At the desired 

 depth, the vane is rotated at a constant angular velocity, and the 

 torque required for rotation is recorded as a function of angular 

 displacement. The peak torque measured is related to the undrained 

 shear strength of the soil by assuming (1) that the soil fails along 

 a surface having the shape of a cylinder with diameter and height equal 

 to the width and height of the vane, and (2) that there is essentially 

 no flow of water into or out of the failure zone during the course of 

 the test. Including full shear of the vane top and bottom, and 

 assuming that the undrained shear strength is completely mobilized 

 across each end, the governing equation is 



S = -^ (1) 



^ U W (3H + W) 



where S = undrained soil shear strength 

 u 



T = peak vane torque 



W = vane width 



H = vane height 



The field vane shear test was developed in Sweden in the late 

 1940' s and has been used extensively in Scandanavia and Great Britain 

 to investigate both unstable slopes and bearing capacity failures of 



