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In construction or renovation, underpinning is the process of strengthening 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 design. *The construction of nearby structures necessitates the excavation of soil supporting existing foundations. *To increase the depth or load capacity of existing foundations to support the addition of another storey to the building (above or below grade). *It is more economical, due to land price or otherwise, to work on the present structure's foundation than to build a new one. *Earthquake, flood, drought or other natural causes have caused the structure to move, thereby requiring stabilisation of foundation soils and/or footings. Underpinning may be accomplished by extending the foundation in depth or in breadth so it either rests on a more supportive soil stratum or distributes its load across a greater area. Use of micropiles〔(【引用サイトリンク】title=International Society for Micropiles )〕 and jet grouting are common methods in underpinning. An alternative to underpinning is the strengthening of the soil by the introduction of a grout, including expanding urethane-based engineered structural resins. Underpinning may be necessary where P class (problem) soils in certain areas of the site are encountered. Through semantic change the word underpinning has evolved to encompass all abstract concepts that serve as a foundation. ==Mass Concrete Underpinning== 'Traditional underpinning,' the mass concrete underpinning method is nearly 100 years in age, and the protocol has not changed. This underpinning method strengthens an existing structure's foundation by digging boxes by hand underneath and sequentially pouring concrete in a strategic order. The final result is basically a foundation built underneath the existing foundation. This underpinning method is generally applied when the existing foundation is at a shallow depth, however, the method still works very well even at fifty feet (fifteen metres) deep. The method has not changed since its inception with its use of utilitarian tools such as shovels and post hole diggers. Heavy machinery is not called for in this method due to the tight nature of the boxes being dug. There are several advantages to using this method of underpinning including the simplicity of the engineering, the low cost of labor to produce the result, and the continuity of the structure's uses during construction. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Underpinning」の詳細全文を読む スポンサード リンク
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