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Re: Copy of: Underpinning Ex

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Underpinning of foundation elements is a large part of the work that our
office provides throughout the western US.  There are several options and
the choice depends upon the problem.  If you have a simple soil settlement
or over loading of the soil's bearing capacity, installation of new
continuous grade beam beneath the existing or installation of new pads
beneath the existing continuous footing.  Thc choice between these two is
dependent upon the state or capacity of the existing footing and it's
ability to span between new pad footings.  Re-leveling of a structure that
has suffered differential settlement is another topic and should be
seriously considered.

Another type of underpinning available for foundations in good condition
and when the soil is creeping or slope failure.  In this case you want to
install "piles" to vertically support the building and possibably the
lateral forces due to slope creep or failure.  Depending upon  the level of
soils investigation and engineering properties determined, we design a
"hybrid" system for installation.  

The system that uses a screw element assumes that you install this like a
cork screw into the soil and support the vertical load of the structure on
the flukes of the screw along the length of the pile, assuming the soils
along the length would support the vertical load.  Another system is a
steel mini pile that is driven to refusal or end bearing.  The classic
solution is a cast inplace reinforced concrete pile that is placed within a
drilled excavation.  

The different methods have their positive points and drawbacks, careful
consideration should be a part of underpinning foundations.

	Bill Warren