Post Tension in Expansive Soil, etc.

[swthwdy]

Please be careful of Post Tension Foundations in expansive clay soil, and especially in the unincorporated areas of Texas. There is no licensing of homebuilders in Texas, and no inspections required in Counties outside of City Limits. We may have a huge problem in the future with the thousands of houses being built in the Counties of Texas.
Some builders cut corners, ignore codes, standards, any existing regulations, and just plainly don't care about good workmanship, just the $ for a finished product.
Our Post Tension Foundation is labeled by our Engineers as "extremely non-uniform" and "economically uncorrectable".
Our builder tried to cover up the defects of our 5 year old Model home.
We have found one tendon that was not stressed, and of course broke when the Post Tension Co. tried to stress it after 5 years, one tendon too deep in the slab, and the r-meter cannot find any other tendons, re-bar, or mesh anywhere in the foundation.
Therefore, we have interior and exterior differential settlement which Post Tension is supposed to at least minimize if constructed correctly.
The State of Texas and Texas Counties are certainly remiss in not regulating homebuilders and inspections of new construction in unincorporated areas.
Professional Engineers and/orASHI Inspectors should seal all new foundations whether Post Tension or regular residential Slab on Grade.
Any discussion?

 

[boo1]

The state of Texas has guide line for post tensioning slabs.

 

[boo1]

See the Texas Section of the American Society of Civil Engineers foundation guides:

http://www.texasce.org/DocumentReview1.cfm

 

[cmcculley]

We do not have a post tension slab and we are having severe cracking in the front section of our home (tile flooring with wide gaps forming and hollow sounding, walls cracking, front porch sinking as well as sidewalk to front door, brick wall wobbly, sink holes around front yard to name a few). My next door neighbor has a post tension slab and they are ok. In researching the area for clay, I found that we are in a very high clay area. I am very concerned that we do not have the post tension foundation, with the expansive soil around. In reading your post, I see that post tension may not be a desirable way to go. I do not live in Texas as you do though. Any input would be appreciated.

 

[swthwdy]

I will try to be helpful to you. Our Engineers say that Post Tensioned foundations are good in expansive soil as far as helping to minimize differential settlement, if constructed correctly. We found through core sampling that the Post Tension cables were not placed in the middle of a 4" slab as they are supposed to be in order to be effective, and there was more than likely no soil sample and no site preparation plan. Post Tension foundations are very much desired if they are constructed correctly using soil sample and design engineering for the specific foundation. We have cracking under windows, fireplace mantle, and floor tiles, in addition to areas of the exterior. My suggestion would be to hire a Geotechnical Engineer ASAP. Good luck.

 

[cmcculley]

Thanks for your advice. I will take it. I have done more research since I posted and have also concluded that hiring a Geotechnical Engineer would be in our best interest.

 

[dadoftrips]

I also have a post tension slab that was incorrectly installed. I have found that the split wedges use to set the cable after tensioning were of different angles. The unskilled laborer just pulled out wedges out of a box of assorted wedges. I believe the issues here is inspection, quality control and performing a task that is atypical to the standard field worker.

My question to this forum is whether there is any technique in slab leveling that can take advantage of the post tension technology? Can existing cables be removed and new cables restrung and tensioned to pullup the slab to a uniform level in all directions?

 

[swthwdy]

Our Structural and Geotechnical Engineers tell us there is no known way to level a PT foundation by removing old cables, placing in new cable and stressing to proper psi.
Even if you are lucky enough to have a design plan for your PT foundation, you cannot be assured that the cables are in their proper location or depth.
If your framing is built to the highs and lows in the foundation, forget trying to level for sure.
Our home has no design plan, one of our cables was never stressed and broke when the supplier tried to stress it after 5 years, the other cables are either too deep or do not exist.
This scenario exists often in the unincorporated areas of Tx. where no required permits or inspections are in place.
It took our home about 5 years to begin cracking and separating both interior and exterior.
Hire a Geotechnical Engineer ASAP.
Good luck to you.
(ponder)