One of the most common questions I’ve gotten in the 15 years of working with clients with Foundation Issues is the following:
What is the best way to properly repair my foundation? We believe the question should be, “what are the things that can be done to make my foundation repairs as permanent as possible?”.
We have found 2 things that can extend the ability of a foundation repair to last.
- Depth is the main key.
- Increase the safety factor for the repair system.
1). Depth is the key.
We hear people say that we are installing the piles into the bedrock soils. In the Jackson MS area, there is no bedrock. We are on clays that extend from 125’ depth and greater. What we have found in being in business for 50 years is that you have to install the piles into the un-weathered yazoo clay (blue clay). It is called that because clay at that depth has never had water intrusion. Oxygen reacts with the clay so the clay is a baby blue color.
If you install your piles into this soil layer, the piles are more permanent and are properly supported on a soil that is less likely to shift/ move with the changes in the moisture content of the soils under your foundation.
If this is the case, then which pile system can we use to reach the necessary depth to underpin, lift and support my foundation?
- Hydraulically Pressed Cylinder Piles (Push Piers)
Hydraulically pressed cylinder piles use the weight of the structure to “push” the cylinders downward.
Pressed cylinders use skin friction along the exterior of the pile to resist movement, similar to a nail. Once the skin friction is greater than the weight of the structure, the residence begins to lift. Depending on the weight of the structure (1 story or 2 story) and conditions of the soils (wet or dry), the depth that this is achieved varies. To be most effective, the pressed cylinders should be pushed to “refusal”.
Using the comparison of a hammer and nail. The hammer is the weight of your house and the nail is the concrete cylinder. The heavier your structure the deeper the piles are installed and if the soils are wetter this decreases the skin friction that allows the piles to be installed to a greater depth.
The concern we have with this system is you cannot control the moisture of the soils and weight of the residence. This can affect the pile depth, and if the piles are not deep enough, the residence could shift when something changes (extreme wet season, drought, change in weight of residence, etc.)
- Helical Pier System
Helical piles resemble a wood screw in that it uses hydraulic drive heads on equipment capable of producing high torque forces to advance the pile into the ground. The piles are constructed in 5’ to 7’ section that connect together to allow the piles to be installed to the desired capacity and depth before a bracket is used to connect the pile to the foundation and the structure is lifted. When properly installed, the helical pile functions like a screw.
The advantage of a screw pile is that it does not need the weight of anything besides the equipment to be heavy enough to resist the torque of installing the pile. With the proper equipment and materials capacity of helical piles can reach an ultimate capacity of 250 kips (250,000 lbs). The other advantage is that the configuration can be adjusted to achieve the necessary depth and capacity of the piles.
We recommend a minimum tip depth of 28’ for the Jackson MS Area and maybe more depending on the capacity of the pile that you are installing.
2) Increase the safety factor
This is done when the residence is lifted and you create a void under the foundation. The foundation is now supported solely on the foundation system only. We have found that if you fill that area with a soil cement or polyurethane foam, it will bring the foundation back in contact with the soils and thus increases the safety factor, decreasing the chance for a call back on repairs.
Filling this void also prevents water from getting under the foundation and creating the same issues, or issues in other areas of the residence.
In working in the Jackson area since 1968, we have found that a deep foundation system to a minimum depth of 28’ and filling the voids after a lift to place the foundation back in contact with the soils, decreases the chance of a call back on our foundation system to less than a 1% chance.
If you have any questions about foundation repairs or concerns for a foundation problem please call us and we will be glad to assist you.