Conventional concrete pit underpinning is accomplished from small, wood sheeted pits constructed beneath the foundation to be supported, typically accessed via an approach pit. Following excavation to the desired level, the pit is filled with concrete to within several inches of the foundation underside. Load transfer is accomplished by dry-packing the gap with stiff mortar.
Engineers can choose from a number of above-grade underpinning techniques during the design phase of the project. Nevertheless, there are circumstances – such as when new construction abuts tight against an existing building – where the conventional concrete underpinning method is often the best or only viable option.