A helical pier is a steel shaft with round helix plates which allow the pier to screw into the ground and provide foundation support for various types of structures.
When it comes to foundation repair, helical piers are drilled into the soil until they reach enough kips, or measurements in force, to support the structure. The pier is then rotated into the ground, and the helix plates generate an axial thrust which causes the pier to advance into the ground. A bracket is then attached to the foundation wall and pier, which allows us to stabilize and support foundations that have settled, heaved, or failed to perform as originally designed.
This foundation repair method is ideal for tying back bowed walls, lifting light structures, and working with sandy soils. With helical piers, you can expect minimal ground disturbance, quick installation with open access, and minimal vibration to the existing structure. Helical piers are usually the choice of structural engineers for older and lightly-loaded structures. They are becoming a better alternative to the traditional concrete caissons for new construction applications in both residential and commercial projects.
Holes are dug at helical placement points to gain access to the foundation, and typically this is done from the exterior of the building but can be done on the interior. If needed, concrete on the foundation will be chipped away to allow for the proper transfer of the loads to the pier. Piers are driven to a minimum embedment or torque as specified by an engineer, or to bedrock or a final torque refusal. Pier depth will vary based on the soils under the structure. Brackets are attached to the pier and foundation to allow for lifting which utilizes a manifold system and helps to synchronize the lifting process. The structure will then be lifted to a maximum practical recovery. Holes are then re-compacted, and the job site is cleaned up. Helical piers are used to hold up a home while the soil is excavated from under it.
Some engineers prefer this system in foundation repair due to measurable torque that is applied to the pier. There is also limited stress applied to the structure which is being repaired. The cons to this foundation repair method include accessibility of the installation equipment and the cost of the material.
The advantages of Helical Piers are that it is an environmentally friendly installation; it can be loaded immediately after install, thereby shortening the job schedule and reducing costs and can be used in sensitive areas. There is no ground disturbance; it is a quick, one-stop installation which can be easily removed and reused. The installation produces no spoils to be disposed of or re-mediated and it involves no cement or curing. However, it does give measurable results and the installation utilizes no impact forces and produces no vibration, which minimizes the risk of damage to adjacent structures.
Helical piers can be used for both residential and commercial applications and are often used in caissons, mini piles, and driven piles. They are also useful when there is structural damage to the foundation, or the structure is built in unstable soil such as cases where the soil has very high water content. Helical piers can also be used when repairing industrial floors; this is because they take a relatively short amount of time and do not cause much disruption to the daily operations of a factory.