with a shear strength approximately three times as strong as category A 

 soil. This design does not lend itself to significant extrapolation due 

 to the high bending stress created at the juncture of the plates. Rough 

 estimates indicate that the maximum practical size would be in the 13.6 Mg 

 (30,000 lbs) to 18 Mg (40,000 lbs) range with a capacity in category A 

 soil of about 1.3kN to 1.8 kN (0.3 to 0.4xlO b lbs). 



Data on the DORIS Mud Anchor (C.G. Doris, 1973) are provided in 

 Table 5. Advertised holding capacities are theoretically predicted; they 

 are not based upon test data. In order to achieve these holding capac- 

 ities with the shear strengths suggested by C.G. Doris (3.4 kPa to 9.6 kPa) 

 the anchors must embed to depths approximately 2 1/2 times their height. 

 Data would be needed to verify this penetration before confidence could be 

 placed in the performance of the extrapolated anchors. 



The DORIS anchor appears to be suitable for very soft sediments where 

 soil shear strength is relatively uniform or increases very slowly with 

 depth. In normally consolidated soils like category A soil, there is a 

 definite advantage to deep penetration. Bearing area for the DORIS anchor 

 is roughly 1 1/2 times that for comparably weighted fluked and pick anchors, 

 yet penetration of the latter would seem to be much greater. This would 

 more than offset the area advantage of the DORIS. This is substantiated 

 by the difference of more than a factor of 2 in efficiencies between the 

 fluked or pick types and the DORIS anchor. 



Large anchor-bearing areas are employed for the DORIS'anchors to 

 achieve high capacities with shallow burial. This results in low steel 

 stress. The advantages of the DORIS anchor should be more fully realized 

 in the very high load ranges where the fluked and pick type anchors become 

 steel stress limited. The point at which this occurs in the DORIS anchor 

 cannot be determined because plate thicknesses and steel types are unknown. 



Extrapolation of the DORIS anchor to the ultra large sizes required 

 by 0TEC cannot be made with a great deal of confidence by maintaining 

 geometric similarity. Extrapolation on this basis assumes that anchoring 

 efficiency remains constant, until limited by steel stress. As dimensions 

 increase by W''-^, bearing area increases as Vir/3. Thus, for constant 

 efficiency, penetration must.increase. According to company data (Table 5), 

 bearing area increases as W ' to maintain constant efficiency (i.e., not 

 geometrically similar). This means that fluke thickness is increasing at 

 a rate less than W'' which results in a more rapid increase in steel stress 

 than would occur if similarity were maintained. In other words, the 

 company probably assumed that penetraton would not increase enough to main- 

 tain constant efficienty. Therefore, the increase in bearing area had to 

 be disproportionately large (larger than W^/3); and thickness relatively 

 small. It is apparent that this offsets the advantage of maintaining low 

 bearing pressure to produce low steel stress. Even though extrapolation is 

 uncertain, the general size of some large anchors have been calculated and 

 are presented in Table 6 solely to enable estimates of fabrication and 

 logistics difficulties. Assuming geometric similarity is not maintained, 

 bearing areas and holding capacities were scaled according to Vr' ' and 

 23W- 9 , respectively (Valent et al . , 1976). The ratio of fluke height to 



16 



