When a boat starts to sink, there’s no mystery about the cause. Water is obviously leaking into the vessel, making it too heavy to float. When a house starts to sink or settle, it’s not because the house has become too heavy.
The soil that the house was built upon is the problem. Soil composition and characteristics vary much more than the composition and characteristics of fresh and salt water. For example, sandy gravel soil has a bearing capacity of around 5000lb./sq.ft. But soil composed mostly of silt and clay can have a bearing capacity of just 2000lb./sq.ft.
If a house has mistakenly been built on soil that has very low bearing capacity, there’s a good chance that the house may sink or settle at some point. Unfortunately, this settlement is typically uneven. Sinking will occur in one area but not in another, or there will be more substantial settling in one area than another. As a result of this inconsistency, one part of the foundation remains in its original position, while another section cracks and sinks. A main section of the house may remain stationary, while a later addition or a chimney tilts on unstable soil. Problems like these keep foundation repair contractors busy.
Fortunately, there are proven techniques for stabilizing houses that have had settlement damage. Following a soil survey to determine soil characteristics, a foundation repair expert may recommend stabilizing a sinking foundation with helical piers. Other names are also used for these piers. Depending on who you’re talking to, helical piers are sometimes called helical anchors, helix piers, helical piles and helix anchors. Regardless of the label used, this type of pier has a distinctive anatomy that gives the pier its name.
Like other foundation piers, a helical pier has a cylindrical shaft. But along the round shaft are several helical plates that are welded in place. The plates -also known as blades - look and work like the threads of a screw. Thanks to the helical form of these plates, the pier is installed by twisting it into the soil like a giant screw. As the pier is screwed into place, pier extensions are added as necessary until the helical pier section reaches a depth where engineers have found stable soil. The "threads" or helical plates grip the soil and permanently anchor the pier in place.
Once the pier has been installed, a steel bracket connected to the pier is secured against the foundation to stabilize it. In some cases, the foundation repair contractor may jack the foundation up to get it closer to its original position before securing the bracket.
This type of pier can be driven into the soil horizontally or at an angle; it doesn’t just have to be used vertically. When used horizontally or at an angle, helical anchors are effective at reinforcing retaining walls and foundation walls. In all applications, a hot-dipped galvanized coating helps to protect the pier from rusting.
Article written by: Samantha Walton
Published: 12/16/2010
