## Estimation of OCR by using any soil parameter

## Estimation of OCR by using any soil parameter

(OP)

Hi,

I'm desperately searching some method to estiamte value of OCR by using any other soil parameter as undrained shear strength, effective shear strength, angle of shearing resistance, effective angle of shearing resistance etc.

I'm desperately searching some method to estiamte value of OCR by using any other soil parameter as undrained shear strength, effective shear strength, angle of shearing resistance, effective angle of shearing resistance etc.

## RE: Estimation of OCR by using any soil parameter

That can also be done with the CPT. You can download Peter Robertson's CPT manual from Gregg Drilling's web site - gratis.

http:/

As I recall, Robertson's CPT approach works much the same way as what's described above.

What do you want the OCR for?

Regards,

DRG

## RE: Estimation of OCR by using any soil parameter

f-d

¡papá gordo ain't no madre flaca!

## RE: Estimation of OCR by using any soil parameter

If it's wetter than LL, it's never felt much overburden at all, and quite probably is NC.

## RE: Estimation of OCR by using any soil parameter

I do check liquid limit and natural moisture content for this very reason, but am also blessed by having a good lab (well and some experience).

Point taken dg.

f-d

¡papá gordo ain't no madre flaca!

## RE: Estimation of OCR by using any soil parameter

Thank you both for your replies.

I need OCR to calculate a parameter for Soft Soil Model i Plaxis. I'm writing a diploma about working platforms and I need some calculations in MES. But I have a problem with one parameter - modified swelling index (kappa*).

I want to use an equation 6 Table 7.1a from material manual for Plaxis 8:

kappa* = 2Cr/2.3(1+e)

so that I need a Cr:

Cr = (e1-e2)/log(sigma'p/sigma'1)

In above equation I have everything except sigma'p, but I found out that I can calculate it if I have OCR from equation:

OCR = sigma p/gamma*z

If you have any suggestions how to solve my problem, I'll be really grateful

Regards,

Kate

## RE: Estimation of OCR by using any soil parameter

"Cr = (e1-e2)/log(sigma'p/sigma'1)

In above equation I have everything except sigma'p, but I found out that I can calculate it if I have OCR from equation:

OCR = sigma p/gamma*z

Do you have a consolidation test with rebound? If so, you have Cr and sigma'p as directly as possible.

By definition, OCR is sigma'p/[sigma' at present]. The denominator is (assuming a single layer) gamma*depth - u. The OCR equation you have seems to be neglecting the pore pressure u. If there is no pore pressure, then the present value of sigma' is gamma*z (assuming z is the depth), or total stress = effective stress.

Have never used Plaxis, so I don't know what its soft soil model is like. Does Plaxis understand pore water pressure? Our people use FLAC, and we go for the simplest models we can justify for any particular case, often just elasto-plastic Mohr-Coulomb, but our MC strength is always based on effective stress. (FLAC does understand water tables, gridded pore pressure, etc.)

Also, what is MES?

## RE: Estimation of OCR by using any soil parameter

Thanks again.I must think over what you've write.

I have results form oedometric test, triaxial shear test and particle-size analysis.

It seems that the oedometric test was made without rebound, but I must ask a person who has done it.

Sorry about MES. I was too fast and write a polish shortcut from finite element method (in polish - Metoda Elementów Skończonych).

And about Plaxis - yes it understand pore water pressure. Here you have a general informations about program (2D):

http://www

More you can find on Plaxis site: http://www.plaxis.nl/

Regards,

Kate

## RE: Estimation of OCR by using any soil parameter

f-d

¡papá gordo ain't no madre flaca!

## RE: Estimation of OCR by using any soil parameter

## RE: Estimation of OCR by using any soil parameter

http://w

http://www.pz27.net

## RE: Estimation of OCR by using any soil parameter

Thanks everybody. Tomorrow I'll discuss this problem with my supervisor.

Regards,

Kate

## RE: Estimation of OCR by using any soil parameter

You could also estimate, roughly, by looking at the relationship of Su/p' = 0.23 (approx 0.23 - see Terzaghi, Peck and Mesri). If you know po', you can estimate Su(o) as Su(o)/0.23. If you have Su(ocr), you can estimate p'(ocr) similarly, Then Su(ocr)/Su(o) ~ OCR. Su(ocr) = Su in situ. Su(o) = estimated Su at po'. (I think this is right - I've been on holiday for a couple of weeks . . . .)

## RE: Estimation of OCR by using any soil parameter

C.C. Ladd's SHANSEP shows this as an exponent m being less than 1:

Su/sigma'vc = S(OCR)^m

In other words, if OCR is high, Su is a bit less than directly proportional with precon pressure.

## RE: Estimation of OCR by using any soil parameter

So, you could use 0.2 (or 0.23) and a pocket penetrometer to estimate OCR. I'd think that would be o.k. with stated limitations, that is. . .

Giving props to BigH for mentioning this in the first place, that is. Vacation must have been good for you, eh?

f-d

¡papá gordo ain't no madre flaca!

## RE: Estimation of OCR by using any soil parameter

Since OCR is directly related to geological processes, has anyone try to ask an engineering geologist?

The question is: How much overburden, if any, has been removed?

I 've done it many times...never received an answer...has anyone?

## RE: Estimation of OCR by using any soil parameter

## RE: Estimation of OCR by using any soil parameter

The 0.23 factor (as noted by BigH) is correct, not 0.2. More accurately, the factor is 0.23 +/- 0.04.

When you read different references, it is a bit confusing and you have to sort a few things and connect different concepts to understand the reasoning behind the equations. "dgillet" is correct and the equation is valid for low to moderately over consolidated clays with low to moderate PI and for higher degree of consolidation the equation should be corrected by a factor of OCR^m (as noted by dgillet). This equation is applicable for Su obtained from Triaxial or direct shear test. However, the confusing part for me is that the exact same equation is provided in various references for Su obtained from vane shear tests and there is no correction with OCR^m. I even read in one references that for field vane shear test the m is equal with 1. However, there is no explanation for this. Why is m=1 for field vane test and different for other lab tests (note that we are talking about corrected field vane test results). I personally believe the only reason that various references do not mention anything about correction of OCR^m is that in real life nobody conducts the field vane shear test for soil with high OCR. Therefore, the actual tests always happen for low OCR soils. This is just my assumption and I have not yet seen any reference to confirm or disapprove it.

## RE: Estimation of OCR by using any soil parameter

geoman110: O.K. then. . .

f-d

¡papá gordo ain't no madre flaca!

## RE: Estimation of OCR by using any soil parameter

## RE: Estimation of OCR by using any soil parameter

Your assumptions and conclusions appears correct. However, there is a difference to say the value of m is higher in comparison to consider it constant 1 for field vane test. However, as I mentioned you might be in the right track. Please advise us if you do the math. The other issue to consider is the fact that if OCR is high there is a chance that a field vane test is not conducted unless it is a research project (I am not aware of)