Check out two papers in ASCE Journal of Geotechnical and Environmental Engineering, May 2000, Vol 125, No. 5. Papers by Eid, Stark, Evans and Sherry. Also, there was a preliminary draft of a paper I saw for one of the Canadian Geotechnical Conferences (this year, likely) by Fabius and Matich. I can try finding out the paper in a couple of weeks when I return from vacation - it is a very interesting paper on the subject. You could also try to call M. Fabius in Thunder Bay, Onario. (Mike - hope you don't mind!)