With a slab-on-grade foundation, the most common failure is perimeter settlement. This failure is the result of either poor compaction, tree effects, droughts or slope failures. In response to this settlement, a common practice of the foundation repair industry is to underpin the perimeter grade beam of a building or house and lift it up to a more acceptable position with remedial underpinning supporting the foundation at the perimeter grade beam.
The result is a change in load distribution. Instead of an equal distribution of load across the bearing soil, half of the load is being carried by the perimeter underpinning with the other half shifted to a smaller area of interior soil. What many times happens over a long period of time, is settlement at the interior because the malleable clay under the interior slab will deform when introduced to the now heavier load.
Prevention of this type of interior settlement can many times be achieved by filling the void, created by lifting the perimeter, with a soil/cement grout. This process normally requires drilling 2" diameter holes through the slab or grade beam and then injecting a soil/cement grout to fill voids, and continuing this pressure injection, lifting the slab to a more acceptable position.
Description & Photos
of structural Problems