Give this ASTM Committee a try. They may have some leads. I'd also look into similar organizations in countries that do a lot of cone work.

http://www.astm.org/COMMITTEE/D18.htm

Thanks.

Check out the work by Dr. Paul Mayne, Georgia Tech University. He has a web site that you should be able to find with google and you can download a number of his publications there.

As stated previously, check Dr Mayne's website.
He has some interesting research and informative power point files.

Also check Dr Campanella's web site at Univ of British Columbia.
Many of his CPT related research papers can be downloaded from his home page and web site.

Do a search on Jim Greig. He did a masters thesis at UBC in the 80's that
was devoted completely to vane testing and CPT correlations.

The proceedings from CPT conference that was held in California (Long beach?) last year has
many CPT and Su related articles. I think they are still available for down load.

In my opinion, the Nkt formula works the best.
Su = (qt - O.S.)/Nkt appears to be the best formula for estimating Su values from CPT testing.

Rolf Larsson with the Swediash Geotechnical Institue also formulated a Su formula that uses the CPT and liquid limit. I have never been able to make this formula work adequately for North American soils.

Coneboy