SPT N correlatuion to phi in rock
SPT N correlatuion to phi in rock
(OP)
Hi all,
I'm looking for SPT N correlation to phi for rocks. The samples I collected ranges from very dense sand, shale & rocks with SPT N 50. Is there any reference online I can refer to ? Bowles has a pretty good correlation table for sand up to SPT 45.
Thanks in advance
I'm looking for SPT N correlation to phi for rocks. The samples I collected ranges from very dense sand, shale & rocks with SPT N 50. Is there any reference online I can refer to ? Bowles has a pretty good correlation table for sand up to SPT 45.
Thanks in advance





RE: SPT N correlatuion to phi in rock
If the material (under a microscope) is angular to subangular, composed of "durable" materials, and is quite dense, then the phi angles are probably quite high (say 40+). Remember that phi is dependent on density, and is not an intrinsic property. Do you "need" phi angles higher than 40?
Be aware that soils with high mica content (10% or more) may not behave as expected. The mica particles are compressible, and one of our most fundamental assumptions about soils and their behavior is that soil grains are incompressible. Also some non-quartz materials may not be as strong, resulting in grain breakage and unexpected settlement if some threshhold bearing pressure is exceeded.
RE: SPT N correlatuion to phi in rock
RE: SPT N correlatuion to phi in rock
Here in NC, our definition of weathered rock is N=100+. Rock is 1 inch penetration for 50 blows. Either one is much more resistance than N=50. At N=50 though, you are probably going to have residual or primary rock texture that is going to control or influence the failure. (Two samples of N=50 could yield wildly different results)
How did you get the samples for testing? This is sort of the range that is difficult to core, and too hard for Shelby tubes.
pigdog
RE: SPT N correlatuion to phi in rock
thanks for the input.
I believed most civil engineers will agree that it's pretty rare to get straight forward answer for any geotechnical problem. It's site specific; one has to visit the site or to be involved in the process to get the full picture. I may have missed out some fine details that may be the most important factor to my problem. I'd like to take this opportunity to thank all you folks out there who took the time and effort to chip in.
p/s, my company uses mazier sampling which is similar to christiensen sampler. I have problems with samples containing losts of fines or gravel. I can't get UD & the recovery is pretty bad.
RE: SPT N correlatuion to phi in rock
RE: SPT N correlatuion to phi in rock
RE: SPT N correlatuion to phi in rock
You suggest that you don't get straight answers from geotechnical engineers so I will be straightforward. The answer to your question is really very simple. There is no relationship between the standard penetration test and the friction angle of rock and from soil mechanics or rock mechanics theory there should not be any relationship. I think we expect too much of banging a hammer on the ground.
jim
RE: SPT N correlatuion to phi in rock
Can we talk about p-y curves now?
RE: SPT N correlatuion to phi in rock
RE: SPT N correlatuion to phi in rock