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.
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FOUNDATION ON SOIL WITH PVR OF 7-10 INCHES
- Thread starter JCGOO7
- Start date
PVR: Potential Vertical Raise
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.
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.
I'm in San Antonio (and it isn't my report...)![[wink]](/data/assets/smilies/wink.gif "[wink] [wink]")
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?
![[pacman]](/data/assets/smilies/pacman.gif "[pacman] [pacman]")
Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.
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 [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.
- Thread starter
- #4
My geotech engineer designed a foundation plan calling for the select fill and the piers, he is not too fond of the water injection method. He did however suggest that if the chemical injection is done properly, and the soil is retested to verify that desired results were achieved, that this was a good alternative. He did warn about warranty and I am in the process of obtaining estimates to compare. Does anyone know a good reputable company in the Dallas Forth Worth area? I talked to another engineer to get a second opinion and basically said the same thing. He did specify that the elevated slab was the most effective but also the most expensive. I have asked my engineer to also design a foundation plan for an elevated slab to obtain estimates on it and compare. The results will probably help me decide. Any information on cardboard box void will be greatly appreciated since like I said I am not too familiar with this method. Thanks for all your responses.
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