Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


CBR Test

CBR Test

CBR Test

In C.B.R. test you have two important readings (2.54 and 5.08).

To obtain the CBR value we should do the calculations based on the reading for 2.54 right?
But if the value obtained for 5.08 is higher than the value calculated for 2.54 we should repeat the test isn't it?

I constantly have higher values in the 5.08 readings than 2.54.
What could be the problem?
The compaction?
Is it completely wrong to do the calculations with the 5.08 value?

Btw, I'm working with the SAATC methods from Austral Africa.

(I hope I've explained myself in a way you could understand)

RE: CBR Test

Yes, The ASTM Method D1883 is similar in that you calculate the CBR for both and compare. I also have the same issue (getting higher CBR for 0.2 in vs. 0.1 in) but I am often doing the test on soil with fine gravel and I find that causes issues. I don't know what kind of soil you are usually working with but I find I only get higher CBR at 0.1 in when I have a Silt or a Clay sample with little or no fine gravel.

I find it helpful to -

1. During the final compaction lift try to make sure there are not fine gravel particles directly under the area where the piston will be penetrating the sample.

2. Graph the results and do all corrections to the CBR value(for concavity etc.) before you do the comparison.

3. Instead of rerunning the entire test I flip the sample over and do the penetration on the opposite side. Usually I get lower overall CBR values on the flipped side but the CBR at 0.1 in is still lower than the CBR at 0.2 in.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close