Foundation Repair - Disadvantages of Simple Pressed Concrete Pilings
Posted by Craig Milam on Tue, Jan 26, 2010 @ 06:00 AM
Superior Foundation Repair will be examining
disadvantages of various foundation repair methods, over the coming weeks, with an in depth look at why these methods are inferior to Steel Piers. The first type of foundation repair we will expose is the often used method of concrete pressed pilings.
Disadvantages of Concrete Pressed Pilings
In homes with Simple Pressed Concrete Piling Foundation Repair, concrete cylinders are driven underneath the home's foundation one on top of the other using the weight of the slab to press them down until they cannot go any further (known as the point of resistance). Unfortunately, it is impossible to tell what this point of resistance is, it could be bedrock, stable soil or unstable soil. Most engineers agree this method of Foundation Repair is not the correct solution for foundation problems because expansive soil will continue affecting pilings after installation. When the soil expands it can work it's way in between pilings and completely nullify the support this method is intended to provide (see picture above for example of piling displacement).
There is no factor of safety built into Concrete pressed pilings
The factor of safety is defined as "the structural capacity of a system beyond the applied loads or actual loads" by Wikipedia. Because the weight of the structure is used to press the pilings down until they can go no further, simple concrete pressed pilings have a factor of safety ratio of 1:1 which means any significant weight additions, have a great potential to cause foundation instability. According to Wikipedia: "Buildings commonly use a factor of safety of 2.0 for each structural member." This means foundation piers should be able to support the sturcture's weight times 2 at the least. Superior's Steel Pier Method supports a structure's weight comfortably with a safety factor significantly greater than 2 by anchoring the structure to solid bedrock, which prevents future additions in weight to a house, i.e. add-ons, new furniture, etc, from causing any negative affect on a home's foundation. Superior's Steel Piers are Engineer certified.
Pressed Pilings installed in dry or unstable soil may sink upon the introduction of moisture.
Because Texas experiences long periods of dry weather followed by wet weather, the soil moisture content is continuosly changing, causing expansion/contraction of soil (further reading: Article from Geology.com, Blog post on Expansive Soils in Texas, Article from USinspect.com). Therefore pressed pilings inserted into dry soil are unstable from the start. If the point of resistance is on unstable soil, increased moisture can cause the piers to sink further into the ground, or, if the soil is stable, expansion will cause the piers to move.
Oftentimes companies will pre-soak the soil to drive the pressed pilings as deep as possible. This is to prevent the pilings from sinking in times of increased rainfall. Introducing large amounts of water into soil is not good for any home at any time, under any circumstances. Superior's Galvanized Steel Piers are driven through the soil until they reach the bedrock up to 100 feet below the surface, effectively securing a home's foundation to a solid rock, which is unaffected by shrinking and swelling.
Further Reading:
An excellent article on the disadvantages of Simple Pressed Concrete Piers from myfoundationrepairs.com