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My husband and I are about to begin a custom home
in Oklahoma (south of Tulsa). We found, after the initial excavation, that
our soil was "pumping". A soil sample was taken and piering down to the more
stable shale layer at 14.5' was suggested. I would like to know if a
post-tension slab and standard footing could be used in lieu of this piering
option or if it should be used in combination. We have already brought in
30" of fill (minimum) to the site per the soils company. The fill has a
plasticity rating of 9. At this point, we have received so many opinions, we
are not sure what is the right course of action. I realize, this is a big
question. If you cannot help, do you have any suggestions for sources of
information to assist us in this decision?
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This is a design issue that should be addressed
by your structural/Geotechnical engineer.
In my experience, using post tension slab and standard footings on "highly
expansive" soils is not a good solution because of the way these slabs are
designed. They are flexible and you may see large deflections and movements.
Also, because of the relatively low tension in these residential slabs they
are not very effective for structural loads or cracking. In Southern
California there is currently a move away from these slabs (California
design) because of poor performance and very expensive lawsuits.
Good luck |