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RE: augered piles

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Steven:

Expansive clay problems are not necessarily limited to the seasonally variable "active zone" (usually the top 12 to 15 ft.).  In Dallas, for example, we often have profiles of CH clays overlying weathered tan limestone overlying competent "Austin Chalk" grey limestone.  The weathered tan limestone is highly fractured and can periodically carry groundwater.  This groundwater can then migrate upward with capillary action to saturate the overlying CH clays. 

I had one unfortunate project where we followed the geotech recommendations and used belled (under-reamed) piers bearing at depths of about 15 ft.  The piers subsequently heaved several inches and the three story precast concrete and CMU superstructure started to come apart.  We were certain that the pier shafts had failed in tension due to soil heaving.  After several hundred thousand dollars of litigation-driven research and investigation, it was determined that the problem was actually heaving in the clays and shales beneath the bells, at depths of 20 to 30 ft.

Regards,

Stan R. Caldwell, P.E.


Roger,
Assuming your 20' depth of expansive soil is bone dry, could you get moisture down that deep and fully distributed through the soil mass to realize its full (theoretical) expansiveness?

Steven A.
Los Angeles