Remolded clays strength
Remolded clays strength
(OP)
I did some unconfined compression tests in undisturbed and remolded highly overconsolidated clays and the remolded strenghts are much higher than the undisturbed strengths.
Properties for these clays are:
Clays: 60.5%
Silt: 32.7%
Sand: 6.8%
Gravel: 0%
Wn: 34%
LL: 67
LP: 30.4
Ip: 36.6
Results are:
qu (undisturbed) = 142 kPa
E50 (undisturbed) = 16 MPa
qu (remolded) = 223 kPa
E50 (remolded) = 24 MPa
Interesting thing is that I did also some UU triaxial tests for the undisturbed clays: c=108 kPa, phi=8. Clays were above water surface.
Clays were remolded under natural water content so it simulates 85% compaction (Modified Proctor OMC was 22.5%). I was surprised with the results. Means that these clays may perform well as engineering fill since their relative high remolded shear strenght. Assuming 1% of the fill height for settlement estimations, these clays can work well as engineering fill under structures or medium height embankments (althouhg I would use these clays only under small-light structures).
Some thing I realized: based on UU triaxial test results, qu's are similar for the undisturbed and remolded clays (so this gives me an idea about the conservatism of the unconfined compression tests).
What do you think about the results? Are any other parameters that I may need to verify if I want to use these clays as engineering fill?
Thanks !!
Properties for these clays are:
Clays: 60.5%
Silt: 32.7%
Sand: 6.8%
Gravel: 0%
Wn: 34%
LL: 67
LP: 30.4
Ip: 36.6
Results are:
qu (undisturbed) = 142 kPa
E50 (undisturbed) = 16 MPa
qu (remolded) = 223 kPa
E50 (remolded) = 24 MPa
Interesting thing is that I did also some UU triaxial tests for the undisturbed clays: c=108 kPa, phi=8. Clays were above water surface.
Clays were remolded under natural water content so it simulates 85% compaction (Modified Proctor OMC was 22.5%). I was surprised with the results. Means that these clays may perform well as engineering fill since their relative high remolded shear strenght. Assuming 1% of the fill height for settlement estimations, these clays can work well as engineering fill under structures or medium height embankments (althouhg I would use these clays only under small-light structures).
Some thing I realized: based on UU triaxial test results, qu's are similar for the undisturbed and remolded clays (so this gives me an idea about the conservatism of the unconfined compression tests).
What do you think about the results? Are any other parameters that I may need to verify if I want to use these clays as engineering fill?
Thanks !!





RE: Remolded clays strength
RE: Remolded clays strength
RE: Remolded clays strength
As to remolded shear strength, your tests are interesting, but I have not delved into this much than noting the common weakening effect when working on slope stability issues.
RE: Remolded clays strength
Mike Lambert
RE: Remolded clays strength
RE: Remolded clays strength
Were the samples blocky or did they have any visible structure?
Mike Lambert
RE: Remolded clays strength
RE: Remolded clays strength
Mike Lambert
RE: Remolded clays strength
Also I was trying to understand your previous comment about you were thinking that the clays were not highly overconsolidated. I was thinking that once you disturb the clays you bring them to a normally consolidated conditions, that's why you did not expect normally consolidated (remolded) conditions to be higher than overconsolidated (undisturbed) conditions....Maybe this is the reason??
RE: Remolded clays strength
So, for undrained strength you've seen some interesting data and received some good thoughts. For drained strength, I'd consider normally-consolidated, reconstituted drained direct shear testing. I'd use the peak value (if you get one) as that'd be fully-softened. Residual values would be for residual design (i.e., if there's some latent failure).
f-d
ípapß gordo ainÆt no madre flaca!
RE: Remolded clays strength
RE: Remolded clays strength
As for drained strengths, I am beginning to use Stark's fully softened strengths for many of my designs. Although I still prefer CD traix tests.
Mike Lambert
RE: Remolded clays strength
RE: Remolded clays strength
Mike Lambert
RE: Remolded clays strength
RE: Remolded clays strength
Mike Lambert
RE: Remolded clays strength
f-d
ípapß gordo ainÆt no madre flaca!
RE: Remolded clays strength
I agree that a UU test with a confining pressure may or may not be greater than the effective pre-consolidation pressure induced by the remolding/compaction process.
However, if an unconfined compression test is ran, then relative to the confining stress of the test (i.e. 0 psf); the sample is overconsolidated. You agree?
Mike Lambert
RE: Remolded clays strength
Also, regardless the type of test, I got that remolded samples become normally consolidated from Professor Stark notes. I think that Skempton in his Rankine lecture (1964) also talks about this. Remold of clays will affect the orientation of the clay particles (will be re-orientated parallely) and therefore shear strenght will be reduced. So I am understanding this as you are are creating a "new clay" which can be considered as a normally consolidated condition.
RE: Remolded clays strength
RE: Remolded clays strength
RE: Remolded clays strength