At DEI we have had the opportunity to work on foundation repairs for typical spread footing foundations. Most of these repairs have been to wood-framed structures with raised wood floors. Our repair solutions typically come as a part of recommendations from a soils engineer. Repair options include helical piers, cutoff walls, injection grouting, and the brute force method of demolition and rebuild. There are other repair options out there, but these are the methods we have used.
Most of our repair designs at DEI have been for problematic expansive soils, with a few other repair designs for settlement of unconsolidated soils. On the repair jobs we have completed, these conditions have resulted in differential movement. A few of the repairs have been on sites where there were cuts and fills on the site. Cut-and-fill sites can result in softer soils where the fill occurred and consolidated or stiff soils at the cut side of the site. This condition can present a higher probability of differential settlement.
The foundation repair solution DEI has used the most is helical piers. Helical piers are essentially large screws that are installed into the soils below the foundation. The helical pier typically has one or more helix plates (a large screw) with steel shafts. The pier is “screwed” into the soils with equipment that can rotate the steel shaft and helix plates. The helix plate size and quantity are determined based on the soil type and loading. The spacing is determined based on the load capacity of the helical pier and the allowable span for the footings that are supported above. The helical piers are installed to a depth that has the strength to support the design load and into soils with consistent moisture content. The result is the support of the existing foundation in soils with the strength needed. Soils also will have less potential for differential movement because of consistent moisture content.
As always, consult a design professional or contractor experienced in design with helical piers prior to completing any repair design or installation.