holding capacities would have been more than adequate if the desired 

 penetrations had been achieved. From these tests it was evident that 

 the first generation vibratory anchor is not a balanced design; i.e., 

 one that matches the energy required to achieve proper embedment with 

 fluke size to obtain the rated holding capacity in different types 

 of seafloors. 



A vibratory anchor with a balanced design would, for a fixed 

 amount of energy, embed into most seafloors and develop the same rated 

 holding capacity. Unfortunately, in some seafloors, such as coral or 

 rock, the anchor may not be functional because all available energy 

 might be expended with little or no penetration and no consequent 

 holding capacity. However an approach to an optimum vibratory anchor 

 should be possible for most seafloor sediment conditions. To develop 

 such a design, the relationships between fluke size, depth of embedment, 

 breakout force, vibrator driving capability, and soil characteristics 

 must be established for the soil types to be encountered. Once these 

 relationships are established, a vibrator can be selected that has 

 sufficient energy or force to drive different sized flukes to appropriate 

 soil depths to achieve the desired capacity. The resulting vibratory 

 anchor design will utilize a vibrator of one size with a fixed amount 

 of energy available and have different fluke sizes for different seafloor 

 soils (i.e., large flukes for low strength soils and small flukes for 

 high strength soils). This accommodation will best utilize the fixed 

 amount of energy available. 



Analytical Procedure . The sequence of events for the attainment 

 of an optimum vibratory anchorage system was: 



(1) Determine the relationship between breakout force, fluke size, 

 depth of embedment, and soil shear strength for cohesive and non- 

 cohesive sediments. 



(2) Determine the penetration capabilities of the existing vibrator 

 (10 kip force) for various fluke sizes and sediment types. 



(3) Determine the adequacy of the existing vibrator to achieve 

 desired penetration and capacity. 



(4) Determine the most suitable fluke sizes to utilize the fixed 

 amount of force available (10 kip) for both cohesive and cohesionless 

 soils. 



The first step of the optimization was the analysis of the breakout 

 resistance of embedded anchors. An analytical procedure, based on 

 Vesic's (1969) analysis of the problem of the expansion of a spherical 

 cavity close to the surface of a semi-infinite plastic solid, was used 

 to determine the relationships between breakout force, fluke size, depth 



49 



