Twisting The Piers Under Your House Foundation

It’s not very often that a word used on  foundation repair companies websites sends me running for the dictionary. It did today, but more on that in a moment.

OK, if you just can’t wait, the word is “thixotropy.”

If you live in a part of the country where you are bombarded with commercials for foundation repair, you’ve probably heard a relatively new trademarked term “Cable Lock Plus ™.”

Here is how the system works, best I can figure.

A rudimentary drill bit of sorts sometimes called “spiral lock” with a cable attached is affixed to the bottom of the first concrete piling, or casing, then twisted (about 90 degrees per foot) into the ground with a hydraulic ram.

The weight of the existing foundation is used as a fulcrum for the ram. Additional pilings are threaded onto the cable and the twisting and ramming continues to either bedrock or the point of refusal in stable soil.

Once the maximum depth is reached, a cap with the top end of the cable attached is placed atop the pier and the cable is used to cinch the whole stack together into one stable and happy pier. Shims are placed between the cap and the slab to raise or support the foundation.

The claimed advantage to this system is deeper penetration of the pier and thus more skin friction to support the load of the foundation. By measuring the cable length inspectors and you know how deep the pier went.

The claim is also made that the steel cable used is far stronger than steel rebar used in other repair methods and does a better job in controlling horizontal movement of the stack of pilings that make up the pier.

The aforementioned website also claims that this system is safer because:

“Safety factor provided by driving load versus the support load combined with thixotropy insures future performance.”

This would be important to you if you live in earthquake country. Certain types of clay soils practically turn to liquid when shaken or stirred and such properties involve thixotropy.

Now go tell honey-bun that you learned a new word today.

technorati tags:twisted, piers, cable, lock, foundation, concrete, repair, slab, pilings


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