Cast in place concrete foundation walls which are inadequately connected to the floor system, or walls which are subjected to relatively high soil pressures, may fail and move inward. As they move inward they typically develop diagonal cracks at the ends of the walls which may wrap around the corners, and at least one vertical crack near the center. Epoxy injection of these cracks alone will not stabilize the foundation wall.
Bracing a concrete foundation wall with carbon fiber straps is not a viable solution as the top of the straps are not, and can not be, connected into anything. Carbon fiber was developed to reinforce areas of excessive tension stresses within concrete structures, like bridges and buildings, typically in seismic zones and not to provide bracing for foundation walls.
At the ends of the leaning concrete foundation wall, in the area of the diagonal cracking, the integrity of the wall is usually significantly compromised and requires full height bracing with steel beams, along with epoxy injection of the cracks, to restore the integrity of the wall. In areas where the integrity of the foundation wall has not been compromised, the connection between the floor framing and the foundation wall can be restored. One way we typically restore this connection is with steel angles bolted to the foundation wall and the floor joists. The size and spacing of the steel angles, and the required bolting, will vary depending on the height of the foundation wall and the height of the exterior grade.
Tie Back Anchors
There are situations where it may not be possible to brace the foundation wall with a connection to the floor framing. These situations require some type of anchorage back into the soil. These anchors are referred to as tie-back anchors. Helical anchors can be used as tie backs if you can embed them into the soil deep enough to provide adequate resistance. Helical anchors must also be embedded beyond the failure plane of the soil which can be difficult in tough clay. The failure plane is the area of soil behind the foundation wall that moves with the foundation wall as the wall moves in.
In order to control the location of our tie back anchors, and to assure they have adequate resistance, we use what is referred to as “concrete deadman”. We excavate a trench parallel to the foundation wall, beyond the failure plane of the soil, and set reinforcing steel bars in the trench. Holes are drilled through the foundation wall and galvanized threaded rods are run through the foundation wall into the trench. The trench is then filled with concrete. This system provides ample reliable tie back capacity.
Foundation Wall Push Back
In situations where the foundation wall has moved in excessively it may need to be pushed back to a plumb position prior to installing the permanent bracing. We typically recommend this if the wall is more than 3″ or 4″ out of plumb. Pushing the wall back does require excavation at the exterior to relieve the soil pressure. It is not possible to move a foundation wall back to a plumb position against the soil without removing the soil first.