Thursday, April 8, 2010

How Does a Wall Anchor System Straighten a Wall

by C. Sherman Henes and Cassi Henes

Here's a great question from Adam in Littleton, CO:

How does the anchor system you talk about pull the whole wall and not just tear through the concrete into the backfill?

In the case of a typical job where Peak does not do a full excavation on the outside of the home's foundation wall, the soil remains in place. If we were to pull on the anchor as much as required to move the wall back to vertical, then the anchor would almost certainly pull through the wall. This is not; however, what we are doing. We are applying a known force to the wall which is mostly absorbed by the soils on the other side of the wall. It relieves the wall enough that it stops bowing. In many cases, the wall can be brought back to vertical over time. This is because during dry periods, the soilds can shrink away from the wall and relieve the pressure on both the wall and the anchors. If the anchors are tightened during these dry periods, it brings the load in the anchors back up to their installed load and removes the space created by the drying soils. Repeating this cycle can; therefore, straighten the wall over time. In more simple terms, we are not forcing the wall back to a straight position, we are applying gentle, but sustained, load and moving the wall only as much as the surrounding soils will allow.
--Aaron Henes, Systems Specialist

"Bowing walls that require a full excavation are straightened during installation because with the soils removed, there is far less lateral pressure to overcome and the wall has enough internal strength to carry the smaller forces required to straighten the wall".
--Michael Sullivan, P.E.