What are Deep vs. Shallow Foundation Repairs in South Carolina?May 23, 2018
As the foremost authority on foundation repair, CNT, located in Columbia and Charleston, South Carolina, is often asked about sinking foundations and repair. There are two general classes of foundation repair; deep, and shallow. Regardless of the repair type, a repair is of the utmost importance for the life of your home and the safety of your family. In this article, we will discuss the difference between deep and shallow repairs.
What are Deep Foundation Repairs in South Carolina?
Deep repairs, sometimes referred to as underpinning, mostly involve pushing or screwing steel piers into the ground to transfer the support and lift structural elements of a foundation. Deep repairs are most frequently used for lifting concentrated loads, such as footings, and for bypassing unstable layers of soil which are causing recurrent problems with a foundation. Deep foundation repairs involve transferring the foundation’s weight to a different layer of the ground on which it was originally built.
Repairing Foundations with Helical Piers
A helical pier is a steel shaft with round helix plates that provides a foundation support for various types of structures. When the pier is rotated into the ground, the helix plates generate an axial thrust causing the pier to advance into the ground much like a screw into wood. A bracket is attached to the foundation wall and pier, allowing us to stabilize and support foundations that have settled, heaved or failed to perform as originally designed. Helical piers are usually the choice of structural engineers for older and lightly-loaded structures. Helical piers are becoming a better alternative to the traditional concrete caissons for new construction applications in both residential and commercial projects.
The deep-driven steel helical piers are 2-3/8″ or 2-7/8″ diameter sectional pipe piles and are hydraulically rotated into the ground to bear on a rock or a solid soil stratum. The piles are manufactured from high strength carbon steel tubing into standard lengths of 3, 5 and 7 feet, with couplings on the ends that allow them to be connected together to achieve the necessary depth. They are coated with a polyethylene copolymer-based thermoplastic powder coating for corrosion protection.
Installing helical piers is a faster, more efficient process. There is minimal excavation, noise, and can be installed inside or outside the home. As efficient as helical piers are, there are a few limitations.
The main disadvantage is the system’s dependency on existing soil. Helical piers use the soil to pull and place the pier. Foundation experts can keep adding shafts to the pier until proper depth is reached. Bedrock is not essential, but reaching a stable, high-density stratum is.
Another limitation is space. Helical piers have traditionally needed more workspace to install.
Repairing Foundations with Push (Resistance) Piers
A push pier is basically a series of hollow pipes fitted together and pushed into the ground, hence the name push pier. Piers are driven into the ground using a hydraulic ram until it reaches load-bearing stratum. They are then anchored to the structure with pier brackets. The weight of the structure becomes the resistance mass needed to push against the piers. This resistance keeps them in place and creates stability, lift, and leveling for the foundation. These hollow pipes can be reinforced by adding non-shrink grout and rebar, thus increasing the overall lateral stability. Push piers are finalized when the required capacity is reached and/or the foundation begins to move.
Push piers are a viable option for some foundation repair jobs. Most notably, these piers can be installed in tight spaces. The required equipment is all handheld, and piers are fit together as needed to reach load-bearing stratum. Therefore, the required space can be as small as 3’x3’, with a 6’ overhead clearance.
Push piers are also advantageous when repairing a heavy building’s foundation. The heavier structure works well with this system because the piers are “pushed” into the ground using the building’s weight. Two-story homes, brick structures, and commercial buildings provide the needed resistance mass.
What are Shallow Foundation Repairs in South Carolina?
Shallow repairs can be used to address slab-on-grade foundations such as floating slab floors which have settled. Soil modification is a mid-depth repair typically performed in conjunction with shallow repairs. Shallow repairs are best suited for lifting non-concentrated loads such as slab floors. Both shallow foundation repair processes we perform involve injecting material immediately under the foundation concrete to fill voids and raise the foundation as required. The least appreciated of foundation repair methods, shallow repairs are often much more economical and reliable than deep repairs for slab foundations. We perform two types of shallow foundation repairs:
Repairing Foundations with Foam Jacking
Foam jacking is a two-part process where polyurethane foam is injected through holes in the concrete approximately 5/8” in diameter. The concrete is effectively raised with the expansion of the foam. The foam jacking material will expand in the weak soil first to consolidate and cause the dirt to become denser and fill all voids below the concrete. It expands in all directions, sometimes as much as 7 feet, so fewer holes are needed to raise the concrete. The foam is set in 30 minutes. The foam jacking method will not retain moisture so it is not subject to erosion once it is set. Polyurethane foam jacking does not settle due to its lightweight nature. Foam weighs 3-8 pounds per cubic foot.
The benefits of foam jacking include:
- Weighs less. Polyurethane foam weighs less per cubic foot than mud jacking.
- Cost less. 50 – 70% less than concrete replacement costs.
- Less invasive. Foam jacking does not destroy your lawn and you will not need to reseed. No heavy equipment is needed.
- Less Mess. There is no water/mud mess to clean up.
- Less Time. The job can be completed in hours and not days or weeks. Foam jacking is less noisy and takes fewer people to accomplish which translates to fewer costs.
- Waterproof. Foam jacking resists erosion.
Repairing Foundations with Slab/Mud Jacking
Slab jacking, also known as mud jacking or pressure grouting, is a process that consists of pumping a weight-bearing grout into the spaces underneath the settled or damaged concrete, thereby raising and supporting the slab from below. Filling the space beneath the slab lifts it to return to its original position, realigning it with neighboring slabs and resolving unevenness.
To effectively support the weight of settled concrete during slab jacking, foundation repair experts use a cement-based grout that consists primarily of either lime or sand. Small holes are drilled ― ranging from under an inch to several inches in diameter ― through the concrete slab at the site of the damage or settling. These holes are strategically placed to achieve the greatest amount of lift and support from the grout, which is then injected through the holes into the voids beneath the slab. Once voids are filled, the contractor will continue injecting grout to lift the concrete until the slab is level, and then patch and seal the access holes.
To read more about slab/mud jacking, please refer to our article entitled, “What is Mud Jacking?”
A failure to consider the soil around the foundation of your home before construction could cause extensive, expensive damage and could leave the structure uninhabitable. Fixing the problems caused by the soil can be costly and time-consuming. Soil does more than damage your home’s foundation, it can also affect drywall, windows, chimneys, and doors.
Examples of the damage caused by soil around foundation include:
- Hairline cracks in the drywall of rooms throughout the home
- Basement floor cracking
- Mold or mildew in the basement due dampness
- Doors or windows that do not close properly
- Water damage from burst pipes
- Extreme shifting of the floors or walls that leave a home unstable
To read more about soil modification, please refer to our article entitled, “What is the Connection Between Soil and the Stability of Your Home’s Foundation in South Carolina?” Contact the experts at CNT to schedule an appointment for a free estimate. Your home is too valuable to be left to chance.