drained vs/ undrained strength 4

[Jordan2]

Dear Friends,
I have the following theoretical doubt and maybe I am doing a stupid question: let you suppose that by means of triaxial CU tests the effective shear strength parameters (c' & phi') of a saturated clay have been derived. Could I derive from the effective envelope the undrained strength (cu) for the examined stress condition? Is this undrained strength coincident with the available effective shear strength?
Please, let you notice that I am not referring to the values of c(CU) and phi(CU) that I could derive from the same CU test, but as I said to the cu (i.e. with phiu=0).
Thank you in advance for your comments..

 

[GTeng]

According to Wroth and Houlsby, Soil Mechanics-Property Characterization and Analysis Procedures, Proceedings 11th ICSMFE, 1985:
Undrained strength ratio in triaxial compression, su/sigmav0', can be calculated as follows:

su/sigmav0'=(M/2)*(R/r)^Lambda

M=6sin(phi)/(3-sin(phi))
R=overconsolidation ratio from isotropic compression
r=spacing ratio, average 2 for most soils
Lambda typically 0.8 (as in SHANSEP)

Going throught the math, this results in similar undrained strength ratios as the SHANSEP procedure, and the authors make the comment that this relationship is what led to the SHANSEP method.