Underpinning is the temporary support of a structure’s foundation while permanent repairs can be made to it. Since the requirement for underpinning is normally predicated on an existing foundation’s failure or compromise, it involves installing more capable foundation elements than those which currently exist for a structure. A need for underpinning could be caused by unplanned or excessive soil settlement, particularly over a structure’s long service life. Underpinning could be required if the foundation soil’s strength characteristics were over-estimated, or the original foundation’s depth and dimensions were under-designed for the loads actually experienced. Underpinning also may be required for an existing structure’s foundation if adjacent site work will disturb it. An example would be an unforeseen excavation project adjacent to a historical building which has only a shallow foundation.