-2 

 where s = shear strength (FL ) 



-2 

 a' = effective confining stress (FL ) 



a' . = critical confining stress (function of in-situ void 

 ratio) (FL *•) 



cj> = angle of internal friction (degrees) 



Considerations of the critical confining pressures for various 

 sands (Seed and Lee, 1967) and of the water depths causing equivalent 

 hydrostatic pressures which must be overcome to produce cavitation 

 of pore water indicates that for typical sands (relative densities 

 between 30 and 60 percent) and for locations of interest here (water 

 depths between 50 and 500 feet) , the effective confining pressure 

 during rapid shearing will be on the order of 1.5 to 10 kg/cm . For 

 friction angles of 25 to 45 degrees (corresponding to the above 

 relative densities) shear strength as computed from Equation A- 5 

 ranges from 0.7 to 10.0 kg/cm , or 10 to 140 psi. 



Implementation of the above relationships in the calculation of 

 depth of penetration requires the exercise of judgment in selecting 

 values of soil property coefficients. If a homogeneous sediment is 

 assumed, average values must be estimated for a guessed maximum depth 

 of embedment, and revised in a subsequent iteration if the guessed depth 

 is too much in error. Alternatively, Equation A- 2 can be solved 

 incrementally, with values of soil property coefficients which are 

 specified functions of depth and/or velocity; this has been done 

 successfully at NCEL under a separate study. Pertinent projected 

 areas during embedment of the existing SUPSALV sand anchor-projectile 

 are given in Table A-l for the purpose of estimating its penetration 

 behavior. Estimates of the ultimate penetration depth of this 

 projectile for typical conditions are given in Table A- 2 as computed 

 from the relationships derived above. According to these estimates, 

 the present sand anchor-projectile launched with the present launching 

 system will not penetrate sufficiently in medium-dense to dense sands 

 to key (the sand fluke requires a distance at least equal to 2 times 

 its length to key) and hold with usable capacity (at least 12 feet of 

 embedment after keying are required for satisfactory anchor holding 

 performance). The bulk of experimental data obtained to date on the 

 penetration of this projectile in sands indicates that these estimates 

 are somewhat low; penetrations to 10 feet in sand (still insufficient 

 for satisfactory holding performance) have been achieved along with 

 one penetration to 18 feet in a reportedly sandy soil of undetermined 

 composition. On the other hand, experimental penetration depths in 

 seafloor clays of determined strengths have been on the order of the 

 predicted depths. Apparently, the equations or assumed coefficients 

 used to estimate penetration in sands are not altogether accurate. 

 However, the quantitative agreement between experiment and theory on 

 the insufficiency of penetration depth in sands is significant. 



32 



