of embedment and soil characteristics. Vesic's theoretical analysis 

 was chosen because his results show good agreement with model tests 

 of anchor breakout in the case of soft clays and loose sands (both 

 typifying ocean sediments) . 



Vesic's analysis was based upon the assumption that the shape of 

 the slip surface during pullout is as shown in Figure 24. This type 

 of failure is referred to as general shear and as previously mentioned 

 in the Background section, occurs with "shallow" anchors. Vesic's 

 theoretical solution gives the ultimate radial pressure needed to 

 breakout a spherical cavity below the surface of a solid. The relation- 

 ship is as follows: 



q. 



= cN + Yt.DN (1) 



c b q 



where q = radial pressure (holding capacity) 



c = soil cohesion 



N = F 

 c c 



N = F +1/2 D/B 



q q 



F ,F = cavity breakout factors 

 c q 



Y, = buoyant unit weight of the soil 

 b 



D = embedment depth 



B = circular plate diameter 



For each soil, there is a characteristic relative depth D/B 

 (D/B = ratio of depth of embedment to fluke diameter) beyond which 

 anchor plates start behaving as "deep" anchors and beyond which breakout 

 factors reach constant final values (Vesic, 1969). The failure pattern 

 for deep anchors is similar to that occurring under deep foundations 

 and is referred to as a punching type failure. Figure 25. To account 

 for the changes in failure patterns, Vesic's results were tempered with 

 engineering judgment and used in this analysis. The analysis is best 

 explained by referring to Figures 26 and 27 where graphs of long term 

 static breakout force versus depth of embedment for various fluke sizes 

 are presented for an ideal sand and an ideal clay. 



50 



