To simplify the analysis for ideal clay. Figure 26, depth was 

 plotted for a single c/p ratio of 0.5 (c/p = ratio of undrained shear 

 strength to vertical effective pressure) . Most seafloor clays are 

 normally consolidated and can be classified by a constant c/p ratio, 

 whereas most terrestrial clays are overconsolidated and exhibit variable 

 c/p ratios with depth. The results were plotted to separate the cohesive 

 (Fp) and the overburden (Fy) components of the total breakout force 

 (Frr,) and to permit calculation of breakout force for clays with various 

 c/$ ratios. Breakout force was calculated using the breakout factors 

 provided by Vesic, in Equation 1; however, the breakout factor N^, was 

 limited to a maximum value of 12. Previous researchers (McKenzie, 1955; 

 Hansen, 1953) have shown that "deep" anchor blocks exhibit breakout factors 

 N of 11 to 12 which roughly correspond to bearing capacity factors for 

 "deep" foudations (Skempton, 1959). The points at which anchor behavior 

 changes from a shallow to a deep anchor are indicated by slope changes 

 in the lines of equal fluke size. 



Figure 27 presents plots of breakout force versus depth for an 

 ideal sand initially in the loose and dense state corresponding to 

 friction angles of 30 and 40°, respectively. Most seafloor sands are 

 thought to fall within this range. 



As previously mentioned, available data suggest that the limiting 

 relative depth, D/B, in sand, where punching failure begins, may 

 increase from 2 in loose sand to over 10 in dense sand. Seafloor sands 

 will generally be of low density; however, anchor embedment by vibration 

 will cause densif ication. Being moderately conservative, all sands 

 prior to anchor breakout are assumed to be of medium density. It has 

 been shown (Baker and Kondner, 1966; Kalajian, 1969) that sands of 

 medium density will change from a shallow to a deep anchor at a 

 relative depth D/B of approximately 5. Therefore, for relative depths 

 >p/B = 5, the breakout factors N used in Equation 1 are constant. 



The points at which anchor behavior changes from a shallow to a 

 deep anchor (where Ng = const.) are noted by slope changes in the lines 

 of equal fluke size. 



The breakout forces presented are long-term static forces and do 

 not take into account the effects of creep in clays and loading conditions 

 other than static. Modifications of the breakout forces in consideration 

 of these factors will involve considerable engineering judgment and a 

 thorough understanding of the loads applied to the anchor mooring system. 



The second step was to analyze the penetration of vibratory anchors. 

 A simplified method for predicting the depth of embedment is to equate 

 vibrator driving force to static soil resistance. This technique is 

 based on experience gained with vibratory pile drivers, which under 

 tough driving conditions, fail to advance the pile further into the 

 soil when the total weight plus the maximum driving force generated 

 by the vibrator is less than the total static soil resistance to 

 penetration (Schmid, 1969). 



53 



