Injection piers are innovative, dual-purpose tools that foundation repair specialists use to repair foundations that have settled due to weak underlying soil or sinkhole activity. Typically placed 3 to 6 feet apart, they can be used to stabilize a house. Combined with hydraulic jacks, they allow a foundation to be raised to its original level position. In addition, injection piers allow grout (aggregate-free cement) to be forced into the soil around the piers. In effect, injection piers combine foundation underpinning with soil compaction.
Injection piers are available in a variety of designs and sizes, but in general they are rugged steel pipes that can be driven deep into the ground. Heavy steel brackets mounted on top of the piers are fitted under foundation footings. The pipes are perforated at the bottom 8 to 16 feet so that after the pier is installed to the required depth, debris can be flushed out with water. Then grout can be forced down the pipe and out of the perforations into the surrounding soil.