Montmorillonite Soils - Now what?

[studio13]

Really need a sanity check here. Have a project in the Florida panhandle and encountered some fat clays. Review of available maps don't indicate this particular area to be prone to high swelling so wasn't expecting too many issues (but that's why we exist I guess). However, I just got back the atterberg results and I have LL of 103 and 90, with a PI of 68 and 63 respectively. Natural MC are both 28. Blow counts are 33 and 20 respectively, I'm asusming becuase we are way below the shrinkage limit on these. Beyond trying to perform some swell testing here, should we be looking at other tests, concerns, etc...? Is it worthwhile performing some electron microscope testing to confirm the presence of montmorillonite here, or is it one of those, what else could it be type situations? Being in FL, the GWT is relatively shallow, so I'm a little surprised by the relatively low NMC measured even below the GWT. We deal with high swelling soils in TX and CO for this particular client, but nothing with these kinds of AL results, so I want to make sure we're giving it the attention it deserves and not treating it like any other TXDOT PVR type calculation. OR likewise, am I overthinking it? Thanks in advance.

 

[GeoEnvGuy]

Whenever I see these high values for LL and PI I go back to Terzaghi's book and it says you might be in the upper end of Gumbo Clays (Miss, Ark, Texas). With the low NMC have you tried looking at the carbonate content?