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Foundation Underpinning

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I have a job where the architect wants to add a lower level to a structure,
and he wants the lower area to be the same as the upper area.

At the exterior wall, I think this is possible.  Excavate both sides of the
wall, then when you get to the foundation, install a needle-beam/column
system to "unload" the wall (a column or drilled pier on each side of the
wall with a beam punched through).  Continue excavating under the footing,
pour a new footing and wall, then you're done.

Unfortunately, in several locations, there is no access on the opposite side
of the wall from the new lower level (one locations has a very crowded
mechanical room opposite).  I can't think of a way to excavate directly
under the existing footing.

These interior walls are fairly lightly loaded (mostly the weight from tall
interior CMU walls, but no "structure" weight or live load).  The largest
excavation is 7'-0" from bottom of existing footing to finished floor.

One solution I have proposed to the architect is by Atlas systems, Inc.  It
uses a combination of steel resistance piers and helical soil-nails to
underpin an existing foundation, but the lower wall is offset the width of
the wall + 4" (16" offset for a 12" wall).  He wasn't happy about loosing
16", and in one location he really can't loose 16".

Does anyone out there have any suggestions?

----
Jason W. Kilgore, P.E.
Leigh & O'Kane, L.L.C.
jkilgore(--nospam--at)leok.com
(816) 444-3144



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