Pocket Penetrometer/ Undrained Shear Strength 2

[Fayoub]

Why is it that the value achieved using a pocket penetrometer is equivalent to twice the value of the undrained shear strength.
The confusion is that since the pocket penetrometer is penetrated into the soil sample pretty quickly, then shouldn't it be considered an undrained strength ?

 

[geomane]

It is a measure of the unconfined compression strength. The pressure you are creating to push the pocket penetrometer into the soil is sigma(1). There is no confining pressure, sigma(3)=0. Therefore, a plot of the mohr-coulumb failure envelope indicates the radius of the Mohr's circle is the undrained shear strength, which is qu/2.

 

[fattdad]

JMCC3265 has the answer.

f-d

ípapß gordo ainÆt no madre flaca!