CPT pwp dissapation rate

[geodan]

During CPT testing on a current project, the cone was stopped and the pore water pressure was allowed to drop. This was done for several intervals within the clay layer (prone to settlement) in question.

Results were given on a plot with pwp on the y axis and time on the x axis. The resulting drop in pwp over time resembles the consolidation plot (e vs square root time) for a single load.

I am wondering if anyone has any information on how to use this data from the cpt? Can I get a coefficient of consolidation from it? Or a time to 50% consolidated? (which would equal 50% pwp dissapated) Coefficient of permeability? Are there any empirical equations for this data?

The site is a retail project. There is a 50foot thick layer of the clay in question. We have several consolidation tests as well, but I am looking to verify the Cv from the lab test results (which indicates a very fast rate of settlement).

Thanks

 

[SmokeyBear]

geodan, a very good reference is Cone Penetration Testing in Geotechnical Practice, T. Lunne, P.K. Robertson and J.J.M. Powell, 1997, reprinted by Routledge in the USA and Canada. Two warning comments:- Prediction of Cv only within one order of magnitude. Permeability from CPT dissapation is subject to much uncertainty and should only be used as a guide.
Good Luck