- Skirts in cohesionless soil - marginal increase in 

 capacity; optimum length ~ 0.05 B ; interior skirts not 

 needed; exterior skirt helps reduce scour and under- 

 cutting. 



Overturning - Anchor must be designed to prevent overturning. 

 Anchor center of mass should be low; mooring 

 attachment points should be low. 

 - Stabilizing moment > overturning moment 



Cyclic Loading 



- Effect depends on magnitude of cyclic component relative 

 to the quasi-static load as well as the absolute load 

 level . 



- "Porous" deadweight may be less susceptible to mooring 

 line transmitted cyclic loads because drainage path is 

 shortened (pore pressure dissipation occurs more rapidly). 



- Refer to section on plate anchor design for added details; 

 also, see Foss, et al, (1978). 



Other Design Considerations 



- Scour, slumping, wave induced instabilities of the 

 seabed, earthquakes, wave forces on anchors. 



- Degree of attention to these depends on location, water 

 depth, soil type, soil degree of consolidation, seafloor 

 slope. 



b. Anchor Design - Cohesionless Soil 



^' - Anchor designed to realize lateral capacity (R^) 

 according to: 



Rj = (W - F^) tan (4;-5«) + 1/2 K^ Y^ Zg^B 



where: W = submerged anchor wt (F) ; F = uplift force (F) ; 



^ = effective angle of internal friction (degrees); 



K = coefficient of lateral earth pressure. 

 P 



c. Anchor Design Cohesive Soil 



- Anchor designed to yield lateral capacity (R-) according to: 



R, = s A + 2s zB 

 1 uz ua 



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