How do I measure the "active depth" of a swelling clay?

[durtboy505]

Hello all
I wonder what methods are available for determining the thickness of the zone of seasonal moisture content fluctuation or the "active depth" of a moisture-sensitive clay? I have read that this could extend to depths of 40 feet in some situations?
Consulting in Albuquerque, NM, we have tried a variety of methods. Running soil suction potential tests at various depths seems to be the best method at this point.
Anybody have other cost effective ideas?
thanks!

 

[LCruiser]

Depending on what you mean by "cost effective" and the what design life of the structure, you will need to consider climatological differences as well as just "seasonal" differences. This is particularly true in the desert SW where El Nino and La Nina have a large effect. In the NW corner of New Mexico expansive potential has been documented at over 25 feet of depth, for example. I'm not sure about 40 feet, but it would not surprise me.

 

[durtboy505]

LCruiser,
Thank you for correcting me, my question should have addressed long-term moisture changes as well as seasonal ones. I am involved in consulting for commercial, civil, and residential projects all over the southwest. I work on a fair number of "forensics" cases. This issue comes back several times a year. I am still looking for a good method on determing the depth of moisture fluctuation on a site with any real accuracy whether its a seasonal or longer-term cycle.
Anyone want to weigh in?
Durtboy505