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Relationship Between Drained and Undrained parameters

Relationship Between Drained and Undrained parameters

Relationship Between Drained and Undrained parameters

(OP)
Hello there, I have a question to for you guys out there, how do we work out the Effective c' and phi' from a undrained triaxial with PWP.  Is there a formula i can use.  

Thanks

RE: Relationship Between Drained and Undrained parameters

See Chapter 21 of Lambe and Whitman's Soil Mechanics.
   sin(phi)' = tan b where b is angle of line of q-p' plot(two dimensional - sigma1 and sigma3)
   c' = a/cos(phi)' where a is intercept of q-p' plot.
Octahedral stresses (sigma1, sigma3, sigma2) is different.

RE: Relationship Between Drained and Undrained parameters

(OP)
Guys i have a soil sample which is a Clayey Material and i have got results from the CUPP of c'=63kPa and phi'=9.5 deg.  This to me is a bit weird a not to sure what to make of it??

RE: Relationship Between Drained and Undrained parameters

It sounds a bit like I used to see in Indonesia back in the 80s - they run the test too fast and the pore pressures never equalized - i.e., they ran the test in 20 minutes like a quick triaxial - measured the pwp from the transducers - but the readings were bogus. . . .

RE: Relationship Between Drained and Undrained parameters

(OP)
Guys I just do not understand it have 2 ore test come back with s similar result but the thing is that they are not even from the same site and I am getting similar results from the Triaxials, i am thinking there is more to this, any thoughts what we can do

RE: Relationship Between Drained and Undrained parameters

Who is doing your lab testing?  What country ar you in? Again, I would check out their testing times to failure.  To measure pwp in clays, it will take nearly 8 hours or even more to complete one stage for the triaxial.  With phi' equals 9deg - either the material you have is "fully disturbed" and you are measuring the residual friction angle - or the test is too fast and the pwp do not fully equalize across the sample.  Observe them doing a test - when I confronted the tech in Jakarta back in 1988 who, bhy the way, was a graduate of the Asian Institute of Technology outside Bangkok (good school) - he told me that he failed the pwp test in 20 minutes.  I told him it was too fast - he insisted and went to get his book to show me - and I showed him where he had misread - or misunderstood - what the book said.

RE: Relationship Between Drained and Undrained parameters

I agree with BigH.
It might caused by disturbance.
Another reason might be the stress history of the soil. Is it highly overconsolidated? The test must be carried out properly.

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