In reference to the use of triaxial measurements to represent the 

 geometry of a particle, Schulz, et al. (1954) state that they may not 

 be fully adequate but that they are simple and convenient and any more 

 adequate system would be greatly complicated; and that it is highly im- 

 probable that a simple method can be devised to completely describe shape 

 because of the great variability in shape found in natural sediments. 

 Zeigler and Gill (1959) also state that the Corey shape factor may not be 

 the best description of shape but point out, however, that it gives a 

 reasonable correlation with drag coefficients and does indeed show that 

 grains with different shapes plot in a predictable manner on a C D - R e 

 diagram. Zeigler and Gill (1959) used the data on natural sands of 

 Schulz, et al. (1954) to compute graphs and tables of settling velocities 

 of particles with different shape factors. 



Briggs, et al. (1962) felt that although shape can be estimated from 

 grain geometry, in studies of entrainment, transport, and deposition, it 

 should be measured by means of its effect on the hydraulic properties of 

 a similar particle having some ideal shape as suggested by Wadell (1932). 

 Using a smooth sphere of equal nominal diameter, mass density and volume 

 as reference, they developed a Dynamic Shape Factor (McCulloch, et al. 



1960) by dividing the settling velocity of the nominal sphere (V n ) into 

 the settling velocity of the particle (V p ) : 



DSF = (V p /V n ) 2 (7) 



For particles affected by both inertial and viscous forces (1< R e < 500), 

 the shape factor would be of the form: 



DSF = a(V p /V n ) + b(V p /V n ) 2 (8) 



where 



a + b = 1 and (b/a) = R, 



Briggs, et al. (1962) found a good, but not perfect correlation 

 between their hydraulic shape factor (DSF) and the common geometric shape 

 factors, and gives regression formulae for estimation of DSF from triaxial 

 shape factors. McCulloch, et al. (1960) applied a correction to the Corey 

 shape factor depending on the values of the axial ratios, b/a and c/b, 

 which apparently was used by Briggs , et al. ( 1962) in computing the regression 

 formula for this factor. 



