underpinning (See underpin)
1 support from beneath
2 support with evidence or authority or make more certain or confirm; "The stories and claims were born out by the evidence" [syn: corroborate, bear out, support] [also: underpinning, underpinned]
- present participle of underpin
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, e.g. due to decay of wooden piles under the foundation.
- 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.
Underpinning is accomplished by extending the foundation in depth or in breadth so it either rests on a stronger soil stratum or distributes its load across a greater area. Use of micropiles http://www.ismicropiles.org and jet grouting are common methods in underpinning. An alternative to underpinning is the strengthening of the soil by the introduction of a grout. All of these processes are generally expensive and elaborate.
Underpinning may be necessary where P class (problem) soils in certain areas of the site are encountered,
base, basement, basis, bearing wall, bed, bedding, bedrock, brace, buttress, column, floor, flooring, fond, footing, foundation, fundament, fundamental, ground, grounds, groundwork, hardpan, infrastructure, pavement, principle, prop, radical, riprap, rock bottom, root, rudiment, seat, seating, shore, sill, solid ground, solid rock, stay, stereobate, stylobate, substratum, substruction, substructure, terra firma, underbuilding, undercarriage, undergirding, understruction, understructure