Since 2002 Granite Foundation Repair has been installing Helical Piers for residential structures foundation repair. How are Helical Piers installed? What makes Helical Piers so good? These questions are good to know when you are in need of a foundation repair or trying to determine which method to use.
This article is written for the layman, and will not go into the mathematical formulas which form the basis for Helical Piers work guidelines. Helical Piers are also known as Helical Pilings and Screw Pilings.
Helical piers, also known as helical piles or screw piles, are often chosen for foundation repair for several reasons. For one, they are a proven technology. They were developed over 150 years ago in England and used to stabilize structures. A later variant was an application of it referred to as the Anchor Piling.
Anchor pilings are constructed with a square tube and round plate. An anchor piling relies upon soil overburden to prevent pulling the piling from the soil conditions. Typical uses for anchor pilings include tie-downs for tents, retainer walls, mobile home tie-downs, basement wall tie-backs, and telephone poles. Anchor pilings with square rods should not be used by foundation support.
Helical piers are designed to provide strong load-bearing support. The helical design allows them to penetrate deep into the soil, reaching stable, load-bearing layers. This makes them suitable for supporting structures of various sizes and weights.
Helical Pier Construction
A Helical Pier consists of one or more round plates welded to a square or round shaft. The plates are cut and twisted into a helix shape, resembling a single screw thread. Hence, the alternate name for a Helical Pier is a “Screw Pile”. The name for the plate is a “ Helix”. Additional shafts are added to obtain depth. When multiple Helix (plates) are used, they are typically spaced 3 times their diameter along the piling shaft.
Two 10-inch plates will be spaced about 30 inches apart. The first plate is installed near the leading edge of the shaft. The leading edge of the shaft is referred to as a pile toe and is slanted to auger into the ground. When used for foundation support, the shaft is normally a round shape, resembling a pipe. Square shafts are great for anchors but offer poor support for foundations. Square shafts do not have the ability to resist bending under load. Round shafts can resist bending under load.
Helical Pier Work
Helical Piers are literally screwed into the earth using a rotating hydraulic head. Unlike pressed concrete pilings, Helical Piers do not use the resistance of the foundation for installation. There is no pressure or vibration of the foundation during its installment. The process is gentle, yet very effective. The success of the installation process is ultimately based on the pier’s ability to support a stable foundation, which is directly measurable.
To assure reliable support, Helical Piers are installed to a minimum depth (or rock) and minimum rotational torque. Why are both Helical Pier depth as well as torque so important? The minimum Helical Pier installation depth for clay soil is that depth at which there is not a seasonal moisture change. Seasonal moisture change might cause the pier to move with changes in clay soil conditions. It is generally accepted that the depth where no seasonal moisture change occurs is around 12 feet in the Dallas-Ft Worth area.
Rotational torque is used as a measure of the soil’s load-bearing capacity. As the helical plate rests within the soil, torque resistance is a useful measure of the ability of the helical pier to support a load. For Dallas Fort Worth there are tables, that show plate diameter and clay soil load-bearing capacity as they relate to rotational torque.
6 Reasons Why Helical Piers are a Good Method for Underpinning a Residential Structure Foundation
- There is no mechanical stress placed upon the foundation during the installment process. The screwing method uses soil overburden to obtain depth. Contrast this with pressed concrete pilings, which directly use the foundation as an opposing force during the drive of the piling system.
- The installment process can be performed in a small space using a hand-held hydraulic torque head. The torque head is held in position with a long lever arm.
- Helical Piers cause minimal disturbance of vegetation. Less than half of the surface soil is disturbed during the process when compared with a pressed concrete piling. It requires about 2 square feet for the installation of the foundation support bracket. A pressed concrete piling installation requires an excavation of 5 square feet.
- A quick installment process means less foot traffic upon the lawn of the foundation support system. The process does not require curing time or extensive excavation, which means that the foundation repair project can be completed more efficiently compared to some alternative methods.
- Can be installed in all types of weather. Unlike some other foundation repair methods that may be affected by weather conditions, helical piers can be installed on a structure year-round. This is because their process is not significantly impacted by factors such as rain or freezing temperatures.
- Work on Helical Piers can be achieved to a known load-bearing capacity. Rotational torque provides a direct measurement of the soil load-bearing capacity. Contrast this with pressed concrete, which is installed until “refusal”. Refusal means “that depth at which the structure can no longer exert sufficient reaction to the end bearing force of the clay soil”, which must be overcome to drive the concrete pilings to further depth. Pressed concrete piling depth to refusal is dependent upon the weight of the structure, while the depth does not use the structure.
Bottom Line
While helical piers offer several advantages, it’s essential to note that the suitability of any foundation repair method depends on the specific characteristics of the site and the nature of the foundation issues. Consulting with a qualified professional is crucial to determine the most appropriate solution for a particular situation.
For further information on Helical Piers and foundation repairs, or to schedule a free foundation evaluation (for homeowners) give Granite Foundation Repair a call at 972-412-2171.