Try "Quality Assurance and Quality Control for Waste Containment Facilities" EPA/600/9-93/182, in section on compacted soil liners.  It should be available somewhere on the web.  

CHPaul - a reminder but I'm sure you know.  Clayey soils are almost "never" isotropic - they always show a different vertical and horizontal coefficient of permeability.  The Atterberg is done on remoulded isotropic material.  How would one guess the vertical or horizontal coefficients of permeabilty from it?  I'll be interested in references to anyone finding something on this!

BigH is correct - "macro permeability", rather than "micro permeability", is the real issue.  That is the main reason that the standard double ring infiltrometer (SDRI) was developed.  Once a clay has a I_P greater than about 25, I doubt that the permeability will change significantly with I_P.  Permeability is significantly affected by density - and initial compaction moisture content.

Check out David Daniel's various (numerous?) papers on this subject - he provides a lot of useful information.  And he's a very well respected researcher.

Please see FAQ731-376  by VPL for tips on how to make the best use of Eng-Tips Fora.