underpinning

In construction, underpinning is the process of strengthening and stabilizing the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons:

• The original foundation is simply not strong or stable enough.
• The usage of the structure has changed.
• The properties of the soil supporting the foundation may have changed (possibly through subsidence) or were mischaracterized during planning.
• The construction of nearby structures necessitates the excavation of soil supporting existing foundations.
• It is more economical, due to land price or otherwise, to work on the present structure's foundation than to build a new one.