When a boat starts to sink, there’s no mystery about what’s causing the problem. 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 around and under the house is the problem. Soil composition and characteristics can vary tremendously –much more than the composition of fresh and salt water. For example, soil that is mostly composed of gravel has a load-bearing capacity of around 5000 lb. per sq. ft. At the opposite end of the soil spectrum, soil composed of sandy clay can support just 2000 lb. per sq. ft.
Builders are supposed to have a soil analysis done if they suspect that a house will be built on unstable soil. A soil report is typically done be a licensed geotechnical engineer, who researches the history of the site, takes soil samples, and performs other tests to assess the soil stability and load-bearing capability at different depths and locations. If unstable soil conditions are discovered, a structural engineer consults with the builder or architect to design a foundation that will remain strong and stable in spite of unfavorable soil conditions.
But what if the contractor skips the soil analysis and proceeds to build the house using standard foundation specifications? If the soil shifts, settles or expands, a standard foundation is likely to fail in some way. Unfortunately, what usually happens is that soil settlement and/or movement occurs unevenly. In other words, the soil may settle or compress beneath one section of the foundation, while remaining stable and solid in another. When this happens,foundation footings, walls and floors are likely to crack and sink or shift over the settled soil. In the meantime, sections of the foundation that bear on more stable soil remain in their original positions. Problems like these keep foundation repair contractors busy.
When a foundation failure has occurred, a geotechnical site investigation foundation repair expert will usually recommend that a soil survey be performed to gain a better understanding of what caused the problems and find out where more stable soil is located. Oftentimes, the contractor may recommend stabilizing a sinking foundation using helical piers and steel brackets. Other names are also used for these piers; for example: helical anchors, helix piers, helical piles and helix anchors. Regardless of the label used, this type of pier has a round or rectangular shaft that holds several helical plates that are welded in place. The plates or blades look and work like the threads of a screw. In fact, the pier is installed by twisting it into the soil like a giant screw. Extensions are added as necessary until the helical pier extends through the unstable soil layer and reaches stable soil at greater depth. The “threads” or helical plates grip the stable soil and permanently anchor the pier in place.
Helical piers are often used in new construction to connect the footing for a wall, floor or pier with stable, load-bearing soil. When used in retrofit applications, a steel bracket is attached to the top of the helical pier to connect the pier to the foundation. The settled section of the foundation can often be jacked back to its original position (or close to it) before the bracket is permanently affixed to the pier, holding the foundation in place. A thick, hot-dipped galvanized coating protects piers and brackets from corrosion. Helical piers can be installed in fairly cramped spaces. Once the repair work has been finished, it’s usually out of sight, since the brackets are typically covered with soil and/or patching mortar.