Definition of Deadweight Anchor Failure . This study assumes that a 

 deadweight anchor has failed if: (1) the bearing capacity of the 

 supDorting sediment is exceeded leading to a local or general failure 

 of the deadweight, (2) the lateral load caoacity of the sediment is 

 exceeded leading to excessive permanent lateral displacement of the 

 deadweight, and (3) the total "immediate" and "consolidation" settlement 

 is such that the mooring line attachment ooint to the deadweight is 

 lowered to beneath the pre-existing seafloor surface. (This last mode 

 of failure, that of settlement, has not been treated herein.) Items (1) 

 and (2) separately and individually define any local bearina capacity 

 failure, necessarily involving tilting and some lateral displacement of 

 the deadweight, as a deadweight anchor failure. 



Although the assumed definition of anchor failure does reauire that 

 the deadweight anchor not slide under the ultimate loading condition, the 

 authors allow that this condition may be too stringent. Under certain 

 circumstances it would appear advantageous to design a deadweight anchor 

 to allow some sliding as a mechanism for accommodating peak mooring line 

 loads. Such a sliding system would reguire sufficient area for movement 

 without adversely affecting the ecosystem or other users of the sea. 

 This study has not treated such a sliding deadweight anchor system. 



Approach . The sizing of deadweight anchors of the type reouired for 

 OTEC is dependent primarily on the magnitude of the lateral' load component. 

 This study first evaluates the lateral load caoacity as a funciton of dead- 

 weight anchor width, B, and cutting edge penetration, Z. Then the cutting 

 edges are structurally designed to resist the lateral load applied to them 

 with the prime objective of obtaining the cutting edge thicknesses, t, 

 reguired. When cutting edge thicknesses are available, the load reouired 

 to fully embed the skirts can be calculated. Further, the deadweight 

 configuration can then be optimized to provide the minimum mass reouired 

 to provide a given lateral load capacity. 



Deadweight bearing capacity is treated subseauently to demonstrate 

 that, for a deadweight anchor designed to resist the expected lateral 

 loads for OTEC, bearing capacity failure is not an insurmountable problem. 



Evaluation of Lateral Load Capacity 



Failure Mode . The lateral load capacity of the deadweight anchors wes 

 evaluated assuming the sliding mode pictured in Figure 33. This failure 

 mode is most desirable because the base shearing zone is forcad down into 

 the deepest possible position where the soil shearing strength is greatest 

 for the strength profiles expected. Development of this failure mode is 

 dependent on the ratio of cutting edge spacing to length, b/Z; on the net 

 vertical load magnitude at maximum mooring line load; and on the applied 

 overturning moment. The assumption here is that cutting edge spacing, net 

 vertical load, and overturning moment will be adjusted to ensure develop- 

 ment of the deep, planar failure zone. 



The lateral load capacity was assumed to include resistance from a 

 complete passive wedge failure in front of the leading cutting edge. The 

 existence of a complete wedge assumes no scour about the anchor block. 



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