CBR % from Clegg Readings

Question

CBR % from Clegg Readings

JintyMc (Civil/Environmental)

(OP)

16 Oct 14 04:55

I have a set of clegg impact values (CIV) which i have obtained and recorded and I need to convert them to %CBR Values.
I have used the following formula on each CIV that i have recorded and have the results from them.

% CBR = 0.07(IVxIV)

An example of a result I am getting are as follows:- 0.07(59 x 59) = 243.67

Does this mean that the CBR % is 243.67%? or am I wrong?

I have some Design Specifications that require CBR Value of 30% but all my results are throwing out HIGH readings after the equation so its throwing me alittle.

Can anyone help?

Thanks

BigH (Geotechnical) · Answer 1 · 2014-10-16 20:34:45

It would be interesting to know the types of soil/road base (etc) you are dealing with. I've never used the CIH but there are different weights . . . Are you sure your Clegg Impact number is 59 and, perhaps, not 5.9?? Clegg's chart doesn't go that high from what I can see. Also, as with many correlations, one should try to get a correlation for their particular site (i.e., site specific) or area.

Just wondering if you ever did a google search?
http://web1.cnre.vt.edu/forestry/cofe/documents/20... (see page 3)
http://www.epa.gov/rpdweb00/docs/source-management...
http://journals.hil.unb.ca/index.php/IJFE/article/...
http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290...

JintyMc (Civil/Environmental) · Answer 2 · 2014-10-17 07:44:39

Basically i have undertaken clegg readings at 20m intervals along an old existing stone farm track which I intend on laying tarmac on.
the ground is stone and compacted like concrete and so the readings which i have are high. these readings are correct as there are no decimal places in the readout screen. Clegg hammer used is : 4.5kg CIST/882 CLEGG IMPACT SOIL TESTER.

BigH (Geotechnical) · Answer 3 · 2014-10-18 00:12:55

Then the CBR is meaningless.

Anyway to prove that there are no "soft spots" in the "track" - I would presume that it wasn't an engineered pavement structure so you might get variations from place to place.

You might have better luck doing a Benkelman Beam study - it will tell you the deflections at the test locations along the track - which would tell you how much additional pavement structure is needed. (I chose the BB since it is likely more readily available than a falling weight deflectometer).

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CBR % from Clegg Readings