site; and second, it is necessary to select a characteristic shear 

 strength, density, or friction angle (for use in the equations) given 

 a possibility of strong variation of these quantities with sediment 

 depth. 



Considering the first problem, it would be preferable either to 

 obtain a good quality core and perform laboratory tests, perform a 

 meaningful in-situ test, or undertake a combination of in-situ and labo- 

 ratory testing. If this sort of program cannot be accomplished, it is 

 recommended that at least the type of bottom (cohesive or cohesionless) 

 be determined, either by observing a disturbed grab sample or through 

 a careful geologic interpretation of the general area. 



If the general sediment type is deteirmined to be cohesive, then 

 the use of the soil properties (c and y ) illustrated in Figure 6 is 

 recommended. These properties are low for normally consolidated deep 

 water clays and, when used with Equations 4 and 5, should provide 

 conservative estimates of holding capacities. An exception to the use 

 of Figure 6 would be a region of rapid sediment deposition, such as an 

 active river delta. In this case the soil properties should be meas- 

 ured directly because extremely soft, underconsolidated clays may be 

 encountered. 



If the bottom is determined to be a cohesionless soil, then the 

 use of an angle of internal friction, <}> , of 30 and a buoyant unit 

 weight, Y, J of 60 pcf is recommended. It may be necessary to use these 

 conservative values in almost all sandy bottom situations since good 

 quality sampling of sand is very difficult. 



Given these property distributions it is still necessary to 

 approach the second problem of selecting characteristic or average 

 values for use in the holding capacity equations. This problem is 

 greatest with cohesive soils since their property variations are gener- 

 ally larger. Experience with these soils indicates that reliable 

 results may be obtained if the strength and density are averaged over 

 the entire depth of embedment for a "shallow" anchor. For a "deep" anchor 

 however, there is conflicting data on the depth range over which the 

 strength should be averaged. The data do indicate, however, that con- 

 servative predictions should result if the strength is averaged over a 

 zone above the anchor fluke with a thickness that is the same as the 

 depth at which "deep" behavior begins. 



For a uniform strength profile, of course, the appropriate char- 

 acteristic strength, c, to use in holding capacity calculations is the 

 measured strength. For a profile in which the strength increases 

 linearly from near zero at the surface, that statements of the preceeding 

 paragraph lead directly to the curves of Figure 7. The quantity D/B is 

 determined along with the strength, c at a depth, D, (I.e., at the anchor 

 fluke). Figure 7 is entered and the parameter D /B is obtained. The 

 characteristic strength, c, for use in predicting holding capacity is 



taken as the strength at a distance D above the anchor fluke. For more 



c 

 complex profiles a trial and error procedure may be required to deter- 

 mine the characteristic strength. To simplify the problem, profiles 



11 



