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Stress ratio of normally consolidated clay

Stress ratio of normally consolidated clay

(OP)
Hi all,

Typically the stress ratio (su/σ'v0) for normally consolidated clay is taken in the range of 0.25 to 0.35ish. For several sites where there is no geological explanation for underconsolidation, I have seen ratios as low as 0.20 or even 0.15.

The value of stress ratio is dependent on the mode of shear; 0.25 typically comes from UU triaxial. However, at the sites I mention the stress ratio has also been derived from UU triaxial. I was therefore wondering if anyone knew where this typical 0.25 ratio comes from?

Thanks for any help with the above.

Kind regards,

LRJ.

RE: Stress ratio of normally consolidated clay

LRJ, attached is an extract from Budhu's book which shown in a simple way this correlation. If you take a look at Soil Mechanics in Engineering Practice book from T&P& Mesri (page 167 in the third edition), it explains extensively how this correlation was derived.

RE: Stress ratio of normally consolidated clay

(OP)
Thanks, Okiryu. The extracts you provided appear very useful.

Does the other book you mention (Soil Mechanics in Engineering Practice, 3rd edition) have something different to what you attached? If so, could you reproduce the derivation here please?

RE: Stress ratio of normally consolidated clay

you can measure Su/p via a series of triaxial tests. Just take a normally consolidated sample and run three CU tests at different confinement pressures.

I'd be more likely to see ratios of 0.2 to 0.25 for the soils I work with.

If you are actually working with overconsolidated samples, you'll get much higher values prior to Pp then it should all revert to typical values.

Jamiolkowski, Turin, Italy is a reference. I think Ladd is prominent in this field too?

f-d

ípapß gordo ainÆt no madre flaca!

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