Today, most residential foundations are made of concrete. The typical foundation actually rests on the ground and is referred to as a slab-on-grade foundation or a floating foundation. As we all know, the soils move up and down. A slab that rests directly on the soil will move up and down with the soil, just as a boat moves up and down on the waves, which is why slab-on-grade foundations are sometimes call floating slabs. If you have a contemporary concrete foundation that was built after 1980 inside of a city, you most likely have an engineered slab-on-grade that has proper reinforcing and adequate stiffening beams, usually called grade beams.
Just as a doctor’s first step before any treatment is to take your temperature, a contractor’s first step, before any repairs, should be to take an elevation survey. For a foundation repair contractor, the elevation survey is essential information. If you do not know what is wrong, how do you know what to fix? The elevation survey will show how far out of level a foundation is. For an experienced contractor, the shape of the foundation, as revealed by the elevation survey, will often indicate whether the foundation has been sinking, moving up, if there might be plumbing leaks, and other useful information.
Once it has been determined that part of a foundation needs to be lifted, the first step is to install pilings. Pilings are made of either steel cylinders (sections of pipe) or concrete cylinders. Every 6 to 12 feet (this depends on the foundation and locations of the pilings, either interior or exterior) pilings are driven into the ground using hydraulic equipment. Some pilings have brackets that extend out from underneath a foundation, while others are driven directly beneath a foundation. Once all necessary pilings are installed, hydraulic jacks are used to lift. For extensive repairs, complex manifolded hydraulic systems are used. Such systems can allow a single person at a control to lift an entire house. The process is amazing!
Settlement
Once it has been determined that part of a foundation needs to be lifted, the first step is to install pilings. Pilings are made of either steel cylinders (sections of pipe) or concrete cylinders. Every 6 to 12 feet (this depends on the foundation and locations of the pilings, either interior or exterior) pilings are driven into the ground using hydraulic equipment. Some pilings have brackets that extend out from underneath a foundation, while others are driven directly beneath a foundation. Once all necessary pilings are installed, hydraulic jacks are used to lift. For extensive repairs, complex manifolded hydraulic systems are used. Such systems can allow a single person at a control to lift an entire house. The process is amazing!
The key to the entire process is getting the right number of pilings in the right locations and then driving the pilings to a proper depth. After a foundation is lifted, the pilings are locked in place and then buried.
When a foundation has been pushed up, the repair process is more complicated. When foundations were not built to contemporary standards, there are special problems that need different techniques.
Heaving
Once it has been determined that a foundation is actually going up, or heaving, the next step is to see if there are any water sources around the foundation. Water sources include sewer leaks, water line leaks, water from poor drainage, water from pools, and water from any other source. If water sources are identified, they should be stopped. Stopping water might involve plumbing repairs or drainage improvements. Once known water problems have been dealt with, a foundation should be allowed to sit and should be remeasured every 90 days to see if the foundation stops heaving or at least returns to a more level position.
If a foundation does not return to an acceptable position, then a full lift is often needed. A full lift means underpinning an entire foundation, lifting it to a level position, and then creating a void space under the entire foundation by lifting the whole foundation an additional 4 to 8 inches. When an entire foundation is lifted, the plumbing needs to be exposed so that it will not be pulled apart by the lifting. To expose plumbing, tunnels need to be dug under a home. The plumbing tunnels can be extended and used to reach the locations for interior pilings.
Special Problems
If you live in an unincorporated area or in an older home, typically one built in the 1960s or earlier, you are likely to have a foundation that was not built to contemporary standards. Bluntly, such foundations are often weaker than newer foundations. Older foundations have fewer stiffening beams, smaller stiffening beams, and often less reinforcing. The worst foundations that I have seen have no beams and little or no reinforcing.
To lift a slab with no interior beams, there are two basic approaches. One approach is to dig parallel tunnels under a foundation, attach steel “I” beams to the bottom of a foundation, and then drive pilings against the beams. With additional pilings under perimeter concrete beams, all or a portion of a weak foundation can be lifted. Tunnels used to install steel beams can also be used to expose plumbing.
Once all pilings are in place, and for a whole house this is typically going to be 40 to 80 pilings, a foundation can be lifted. The most advanced lifting techniques involve using hydraulic systems that are connected by hoses to control panels and pumps. Usually, a single man working with a crew of 5 or 6 men can lift an entire house!
The key to the entire process is getting the right number of pilings in the right locations and then driving the pilings to a proper depth. After a foundation is lifted, pilings are locked in place and then buried. Plumbing is hung from the bottom of a slab, drains are installed in tunnels, and tunnels are sealed.
The second approach is to install pilings around the perimeter of a foundation and then to use polyurethane foam to lift the interior. The polyurethane foam is injected through small holes. For limited lifts, polyurethane can be a cost-effective approach. For substantial lifts, the cost of polyurethane can become prohibitive.
If you think you are having foundation problems, call us at Advanced Foundation Repair. Our evaluations include preparing a foundation survey and a contour diagram and are free!