Do I Have to Pack up My House Before Foundation Work Begins?
Ask a Registered Professional Engineer Series
By: Donald J Clayton, PE – Registration No. TX37112
“Must I Pack Everything”
“My husband and I have signed a contract to repair our foundation. I am very worried about damage to photos and items on the walls and shelves. Must I pack everything safely away before the work starts?”
As the lady of the house, I know that you want your house to be restored like it was when it was new. Your concern about your important belongings being disturbed during foundation repair work is understandable. After many years of designing foundation repair plans, writing specifications, inspecting foundation repair work, and actually supervising restoration, I have never seen any decorative items fall from a wall or topple from a shelf or mantle.
In fact, a typical foundation repair and restoration is quite easy and smooth. If you have a valuable items that are priceless to you, you can absolutely protect them by packing or moving them. However, please know that the items within your home are safe.
Let’s Talk About Foundation Repair
Most homeowners never have to go through the experience of having their foundation repaired. Therefore, it is understandable that you have some fear of a construction process of which you are not familiar.
For our discussion today, we will concentrate on manufactured steel piers. There are multiple different types of repair methods on the market today, as well as many different price points. Additionally, there are some companies offering inexpensive repairs that may, or may not be effective for the long-term. These repairs simply aren’t recommended by engineers for long-term support.
The discussion here will concentrate on engineered foundation systems that are installed to published specifications and tested during installation. This insures that the pier has suitable load- bearing capacity and confirms that the underpinning will support a load in excess of the force needed to life and restore the floor.
Now is an excellent opportunity for you to learn about each step in the foundation underpinning process, and how recovery of the lost floor elevation is accomplished.
Engineers often prepare written specifications for how the foundation work is to be performed. While each repair project, design, and foundation repair contractor is different, the steps required to complete a quality foundation restoration are quite similar.
As an example of what the engineering community expects from a foundation repair contractor is outlined below. While there will be variances, each step of the process is explained here in order to help you understand how the foundation repair process works, and how lost floor elevation is recovered. Follow along to learn what to expect before the work on your house begins!
Slab and Pier & Beam Foundations
Houses built upon reinforced concrete slabs, or foundations built with a crawl space under the floor (Pier & Beam Foundations) will have soil excavated to gain access to the concrete support beam before pier installation can begin. These types of foundations require only a small hand-excavated access hole at wherever a pier is specified on the repair plan.
A conscientious installer will carefully removed the sod or decorative plants near the house where each excavation is specified. The landscape material will be stored and protected. In addition, the soil that is removed during excavation will be placed on a plastic, or another material, to preserve the soil. After the work has been completed, the soil and plant materials will be returned to the original locations. Not only will your landscaping look the same after the work, but the site will be clean and neat.
When the house has a basement, there are two options to access the foundation beam. The method selected will depend on the structure, the foundation, and the job site. When repairing a settled basement, access to the bottom of the foundation beam is more difficult than on a slab foundation. In any case, once the basement excavation is completed, the remainder of the pier installation and restoration process is the same.
EXTERIOR ACCESS- Access from the exterior requires a deep excavation from ground level to the bottom of the concrete foundation. The excavation process usually requires a mini-excavator to remove the soil The soil that removed will be stored for replacement. Deep excavations can require shoring (props for support) for worker safety.
INTERIOR ACCESS- Access from the interior of the basement is another method used to install high-quality steel underpinning. The contractor will cut small holes in the basement floor to gain access to the underlying soil for excavation. Unfortunately cutting and removing the concrete will create noise and dust. The access holes that are cut into the concrete floor typically measure about three feet by three feet.
Following the removal of the broken concrete, the access hole required for pier installation is hand excavated. Again, soil that is excavated is safely stored until it is time for replacement.
Once the bottom of the concrete foundation beam is exposed, the concrete must be prepared for mounting a steel foundation bracket. The steel bracket is used to transfer the weight of the house from the failing soil to the steel pier system. Preparation for mounting a bracket often involves smoothing out the rough, uneven vertical face of the concrete beam, along with leveling the bottom of the foundation beam. This is because concrete foundations are usually cast in a trench that is dug in the soil, and this excavation method is not always smooth or level. This causes the sides and the bottom of the concrete beam to be uneven and rough. The smoothing and leveling process is required for proper load transfer from the house to the bracket, and from the bracket, to the pier.
The contractor will carefully prepare the concrete at the point of attachment using power and hand tools. After the concrete preparation, the pier bracket is carefully aligned on the vertical face and leveled under the beam. The steel foundation bracket can be permanently bolted to the foundation now, or later. Cutting the concrete basement slab and drilling bracket mounting holes can cause a sound inside the house during the work, but no foundation movement or noticeable vibrations will be felt or seen.
Installing the Underpinning
Once the pier placement locations have been excavated and the foundation bracket preparation are complete, the pier installation can begin. Once again, the type of underpinning product dictates the installation method. Regardless of the manufactured underpinning product specified, the installation will be smooth and without vibration. The occupants and items on the walls or shelves will not be disturbed.
Steel Resistance Piers
All steel resistance pier equipment and pier product easily fits into a wheelbarrow. There is no need to be concerned about heavy equipment on, or around your house. Steel resistance piers are made from high-strength structural tubing. The piers are gently advanced into the soil using a portable hydraulic pump and hydraulic cylinder. The sound made by the hydraulic pump isn’t much different than the sound of a gasoline lawnmower. The process is smooth and free of any vibrations.
Helical Screw Piles
A helical screw pile is installed differently than a steel resistance pier. A helical screw pile is something like a wood screw. It is similar in the wya it looks and the way that it is installed.
The installation process uses a smooth running hydraulic gear motor that rotates the pile shaft to advance steel helical-shaped plates into the soil. Installation continues until the helical plates on the helical screw pile shaft reach suitable load bearing soil, at a pre-determined depth. Depending on the type of construction and the weight of the house, installation might require a handheld gear motor might be used, along with a gas-powered hydraulic pump. Heavier structures require a more robust pile, therefore, larger piles usually need to be installed with a gear motor attached to a small machine, such as a mini excavator.
Once again, the installation of helical screw piles is vibration-free because the hydraulic gear motor rotates at a very slow speed, usually less than 10 revolutions per minute.
As the pile advances into the soil, the load capacity is monitored. This is accomplished by measuring the torsion that is being applied to the shaft as the pile advances into the soil.
Load Transfer and Raising the Foundation
This is the exciting part of the process! After the piers are fully installed, the load capacity is verified, and the installation equipment is removed from the site, construction work is complete! The configuration of equipment used to evenly and gently lift the floor back to level is now put in place.
Hydraulic jacks are located on each pier bracket. These hydraulic jacks are all interconnected through a series of hydraulic hoses and hand pimps, or to a small electric-powered hydraulic pump. Each hose has a cut-off valve located between the hydraulic jack and the pump.
The supervisor will orchestrate restoration from inside the structure. They will constantly monitor the floor elevation and alignment corrections at doors and windows.
Foundation settlement begins from somewhere inside the house. The floor settlement generally increases as one goes toward the exterior wall. The supervisor’s job is to reverse the structural settlement by carefully controlling the amount of floor lift at each hydraulic jack. What this means is that the jacks closest to the point where the floor slope began, will raise the floor very little, while the jacks closest to the point of largest settlement, will raise the most. As the floor begins to return to level, the supervisor will close valves on specific jacks and record the final hydraulic pressure. The restoration continues, slowly and carefully with subsequent valves being closed as the floor becomes more and more level. Normally this begins with jacks near where the slope began, and ends a the location with the largest amount of settlement. The process lifts the foundation millimeter by millimeter to slowly and gently restore the floor to as close to level as the construction permits.
After the flood is level and all hydraulic valves have been closed, each pier is secured with nuts and bolts to a pier cap on each bracket. The jacks, hoses, and pumps are disconnected and removed. At this point, the weight of the house has been successfully transferred from the failed soil underneath the foundation, to the structural steep pier supports. Additionally, the lost elevation has been recovered.
Testing, Inspection, and Cleanup
Depending on the project, a plumbing test might be recommended. If there are plumbing pipes near the area of the floor restoration, a crack or separation of a pipe might have occurred during the lifting process. A test of the domestic water and sewer system would be recommended in this situation as well. Leaks are easily determined when the pier excavations are still open.
In some municipalities, a building inspection is required before the work is accepted. An engineering inspection is sometimes required if the project was installed under the design and specification of a registered engineer.
The excavations are filled and compacted. The landscaping is replaced, and the entire job site is cleaned and left as close to pre-construction condition as possible.
Engineered foundation underpinning is installed to manufacturer’s specifications. Many times they piers are also installed to engineer’s specifications. In both cases, the contractor carefully monitors and measures all aspects of the project. The engineer, if applicable, and the homeowner should receive the following upon completion of the work:
Pier Installation Logs
STEEL RESISTANCE PIERS
The pier installation log is a record of the force required to drive the pier pipe through the soil. Measurement is usually recorded at 3-1/2 foot intervals during installation with the depth to load bearing being recorded. Once a steel resistance pier reaches suitable load bearing soil, a Field Load Test is performed on each pier. The proof load is recorded. The proof load test verifies the pier capacity and insures that the pier will support a force greater than the structural weight of the house.
HELICAL SCREW PILES
The helical screw pile log reports the shaft torsion that occurred at various depth intervals during the installation of the pile. Once the target depth was reached, the terminal torsion is determined by averaging the shaft torsion during the final three feet of the installation. This terminal torsion value is provided to accurately and empirically determine the ultimate load capacity of the helical screw pile installation. The empirical load capacity must be higher than the load placed on the pile by the structure at lifting. This insures a factor of safety against future settlement and long-term stability.
The contractor will supply a log of the final force applied to each hydraulic lifting jack during restoration. A measurement of the amount of foundation lift is recorded at each pier location. Many contractors also provide a floor plan of the restored area with the final elevations noted. This plan is valuable if any future floor movement appears.
The contractor shall supply an installation workmanship and service warranty along with the manufacturer’s warranty agains defects in pier materials or workmanship.
Your Experience Can be Different
The information provided here, and the procedures described above are a template to introduce you to the process involved in underpinning a foundation, and how lost floor elevation is recovered. Keep in mind that are a few key differences with every project, such as:
- Structures are architecturally different
- Lot configurations are not the same
- Quality of construction varies
- Amount and extent of settlement is different
- Foundation contractors have different experience
- Underpinning products are not all the same
You now have information to be able to ask intelligent questions about the foundation work that is proposed. If you are dealing directly with a foundation contractor, ask him or her to provide a detailed explanation of the work and the equipment that will be used for our specific job. When you choose to install a high-quality manufactured steel support, you should ask to see certificates of completed factory training proving that the job supervisor and other workers are factory-trained and certified for the products that they are working with.
In addition, you should ask for the website address of the underpinning manufacturer. From their website, you should be able to learn about the underpinning product, see case histories of completed projects, read product specifications, and warranties.
To protect yourself and your property, be sure to verify that the contractor has liability insurance and worker’s compensation insurance. Ask the contractor and/or Building Inspection Department if a permit is needed for the work on your home.
All of this brings us back to the question of concern for damage to decorative items on the wall or shelves. With the knowledge you now have, you should feel confident that there will be no shocks or shaking to the house during the repair work, or during the lifting of the floor.