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Copy of: Underpinning Ex

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Underpinning an existing foundation is tricky and requires a lot of 
engineering judgement.  The structure has to be supported while the soil 
beneath the footing is removed and a new foundation (underpinning) is 
installed.  The load has to be transferred to the new foundation in a manner 
that will not result in distress or failure of the existing structure.  In 
transferring the load, I have used steel wedges, later encased in dry packed 
concrete.  Sacrificial screw jacks could also be used, however, I would not 
ever consider just pouring concrete below an existing foundation.

Underpinning a continuous footing is, indeed, costly, but what are the 
choices?  In the case of adding additional stories to the building the 
choices would be either underpin or independently support the addition.

In underpinning a continuous footing supporting masonry, I am very hesitant 
to have more than 4 feet of footing unsupported at any one time.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona