Spread Underpinning.

Occasionally, due to site constraints, underpinning is achieved by spreading the foundation load over a greater area of ground, rather than transferring to a bearing strata at a lower level.

An example undertaken by the authors’ practice was in the restricted cellars of a series of large Victorian properties being redeveloped as office accommodation. The load-bearing walls sat on stepped brick footings, just beneath a cellar floor of compacted earth. In this case it was possible to cut pockets out of these footings, run reinforcement through the holes, and cast the whole of the cellar floor area as a reinforced concrete raft slab. This proved a very cost-effective and practical way of enhancing the load-bearing
capacity of the premises and providing a basement slab at the same time.