FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES
FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES
(OP)
I need information on the best foundation design for this type of soil. I do have a geotech engineer report. I have been given the following options and will like to know which is more effective and economical: removal and refill with select fill up to 60" and 15 foot piers, water or chemical injection to stabilize the soil, or an elevated slab with also 15 ft piers. On the elevated slab I was told about cardboard void boxes but I am not familiar with this method. Please advice. I plan to build in the Cedar Hill area near Dallas that has Eagle Ford Shale type of soil.





RE: FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES
Maybe the first is the best technically since it removes the agent in the depth more likely to cause the heave. This could be a bit dearer than the elevated slab, or not, depending of the contractor. Soil stabilization is of more uncertain result (just my view) (at least if not doing as much work than with removal).
If you don't remove the clay, ensure you use (if feasible) piles with bell caps standing deep enough to sustain (by counterweigh of the soil in the bell standing) any potential adhesion upwards, at competent depth, and this even if you include elements around the pile attempting to reduce the adhesion.
Also, try to load as much as feasible any (pile) foundation point to counterweigh the tendende to go upwards. The big spans should be thought of since inception for these sites; they also may better the behaviour of the elevated structure from their flexibility (more length without restriction in which to accommodate similar amounts of heave); yet in general the foundation should be stiff, to minimize the effects of what under it ongoing.
You might also consider other close alternative solutions, specially a very stiff foundation if the building out of being small or the foundation divisible in cells merits so. This without excluding what above.
RE: FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES
Generally, remove & replace is the least expensive option - but a PVR above 6 inches usually results in a suspended slab design. Carton forms are an inexpensive way to create an air void beneath the beams and slab - they deteriorate over time. But you will need concrete retainer blocks around the perimeter to keep the voids from filling over time.
Chemical treatment is an option, but water injection has a high failure rate. Don't go there! Use a high pH potassium solution; don't go with the low pH sulfonated naphthalene solutions - they are a waste of money for most sites. (You have to keep water out of the treated soils in order for this solution to work in expansive clays.) The high pH potassium solution should be a blend of potassium chloride (active ingredient), sodium hydroxide (raises pH), ammonium lignosulfonate (a very smelly, but effective, wetting agent) and water. Be careful about whom you hire to do chemical treatment - that isn't a level playing field. Ask about verification testing. And if the contractor won't spell out his specific mixture, find someone else...
What did your geotech recommend - or did you just get options?
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES