CBR correlations

[madc]

I want to obtain in-situ CBR values in ground that is likely to comprise +20mm material. Does anyone know of any in-situ tests that could be used instead and then correlated back to a CBR value?

 

[BigH]

The TRRL DCPT is one test used in road works that "correlate" to the in situ CBR.

 

[eric1037]

You can also perform a CBR test in the field directly. This is usually equipment mounted on a truck bumper.

 

[madc]

Thanks, I am actually thinking about what I could do in the field other than the CBR as I'm expecting the ground conditions to consist of a mixture of gravel and cobbles (plus 20mm), so it may not be possible to carry out an in-situ CBR. By substituting a DCP (which I think is generaly just used for existing roads) I was thinking that if cobbles are hit during the test then this would render the test unsuitable too. Any thoughts?

 

[BigH]

Trouble when you are in granular with cobbles, etc. hardly any test will be reliable. What do you need the CBR for? Typically, the CBR >30 is standard if for granular subbase. Fang (Foundation Engineering Handbook - the old Winterkorn and Fang) has correlation chart in it showing CBR vs classification, CPT/SPT, Mod. of Subgrade Reaction, etc. Check it out. Also Baker Highway Engineering Handbook has another correlation chart (similar) but using more highway oriented tests like the R value, etc.