Fiaure 54 illustrates the relationship between the various loads 

 involved with a deadweiaht anchor on sand as a function of the sauare 

 block width. The bearinn capacity, Q, is eaual to the reauired vertical 

 load (Q = Rr - 1.5 R|_). The force Q e , reauired to embed the cuttina 

 edaes, of length Z = 0.05R, is about 25 Dercent of the reouired vertical 

 load, Rr, thus no embedment Droblems are foreseen. In order to achieve 

 the submerged weiciht reauired, Rr, within the assumed anchor dimensions 

 some special weiahtina may be necessary. This is so because the weiaht 

 of a solid, nrestressed concrete block, R by R by 0.1R, is less than 

 the block weiaht, Rr, reauired to achieve a like bearina capacity. The 

 difference in weiaht between RR and R c is relatively small and supplyina 

 that weiahtina, by increased bulk density, should nresent no oroblem. 



Findinas and Conclusions 



1. The ootimum ratio of cuttina edae lenath to sauare deadweiaht 

 side dimension, Z/R, varies primarily with the soil type: 



a. For cohesive soils, the ootimum Z/R ratio is 0.1 



b. For non-cohesive soils, the ootimum Z/R ratio is about 

 0.05 or somewhat less. 



2. Deadweight anchor (sauare) dimensions necessary to maintain OTEC 

 on station ranae between 22 and 60 m depending on the loadina condition 

 and seafloor material (see Table 15). 



3. In order to orevent excessive tiltina of a deadweiaht anchor 

 (local bearina canacity failure), the effective weiaht (vertical force 

 comoonent Rv) aonlied to the seafloor must meet certain minimum values: 



a. For cohesive soils, the reauired weiaht is aiven by Eauation 24. 

 For the cohesive soils and loads considered, the reauired embedment force 



is aooroximately eaual to the aonlied lateral load. 



b. For non-cohesive soils, the required weight is dictated by 

 bearina caoacity, not skirt embedment. To prevent a bearina capacity type 

 failure, a submeraed weiaht of aooroximately 1.5 times the aonlied lateral 

 load is necessary. The tremendous weiaht maanitudes imoosed by this 

 reouirement may be reduced if testina indicates that a failure in the bear- 

 ina canacity mode will not lead to catastrophic anchor failure. Also, the 

 coefficients used in the bearina canacity eauations need verification for 

 the OTEC loadina conditions. Present uncertainties in these coefficients 

 force conservative desian. Model tests to reduce this problem, and hope- 

 fully to enable deadweiaht design to be auided by lateral resistance rather 

 than bearina caoacity in non-cohesive soils, are included in the next Dhase 

 of the OTEC effort. 



4. The conceDt of usina a deadweiaht anchor with cuttina edaes to 

 moor OTEC platforms on sediment seafloors is viable. 



107 



