Correlations between CBR and PI

[sshahnaj]

Correlations between CBR and PI has been found from dynamic cone penetration test with 17.6lb hammer and 22.6in drop height. Are these correlations valid for portable dynamic cone penetrometer with 15lb hammer and 20in drop? If not, is there any way to estimate CBR from the test result of portable dynamic cone penetration test?

Thanks,
Sonia Shahnaj
Berkeley County Gov., SC

 

[jdonville]

We usually estimate CBR using soil classification (particle size and Atterberg limits) data, usually by Group Index. Yes, it's kind of crude, but at low CBRs (fine-grained soils), it usually doesn't make much difference to a slab or pavement design.

Otherwise, grab a sample and perform the Proctor and CBR testing needed to generate the "real" CBR of the subgrade. It'll waste less time than arguing over empirical relations.

Jeff

 

[Ron]

I agree with Jeff...if the expected value is going to make a difference in your design, test it. If not, "guess" it from classification data.


Jeff...I'm expecting some info from BigH that I'll pass on to you.

Ron

 

[fattdad]

For a couple hundred bucks you can just do a CBR test - that's what I'd recommend. I have found MH soils with CBR values of 14 and SC soils with CBR values of 3. The consequence of failure (premature design life) are too great to just guess - unless you just guess a value of 3. Also, there are pretty good correlations between CBR and subgrade modulus so from the CBR test you can help the structural designer with a site-specific modulus value!

Good luck.

f-d

¡papá gordo ain’t no madre flaca!

 

[fattdad]

fattdad (Geotechnical) Feb 12, 2007
For a couple hundred bucks you can just do a CBR test - that's what I'd recommend. I have found MH soils with CBR values of 14 and SC soils with CBR values of 3. The consequence of failure (premature design life) are too great to just guess - unless you just guess a value of 3. Also, there are pretty good correlations between CBR and subgrade modulus so from the CBR test you can help the structural designer with a site-specific modulus value!

Good luck.

f-d




¡papá gordo ain’t no madre flaca!

 

[jdonville]

Ron,

FYI, my personal address is jtdonvilleAThotmailDAWTcom , in case you need it.

"Do the needful" with the uppercase letters.

Jeff

 

[BigH]

jdonville - am still trying to get the CD to you.