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RE: Using shoring as structural member

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Harold Sprague wrote:

[snip]
>Another consideration for the elimination of tiebacks might be a
>cantilevered wall such as a slurry wall, tangent wall, or a secant pile
>wall.  These walls are top installed.  Once they are installed you excavate
>without having to install lagging or tiebacks.
>
>Tangent walls are constructed by drilling caissons or auger cast piles at a
>given spacing and then installing caissons or auger cast piles in between to
>seal off the excavation.  
>
>The secant wall is similar except the first caissons are placed and the
>infill caissons actually cut into the prior installed spaced caissons.  The
>first caissons are placed with no rebar.
>
>I have done walls as tall as 30 feet with no tiebacks using a tangent wall.
>
>Slurry walls are another possibility or slurried precast walls.  Sometimes
>the traditional shores, whalers, lagging, cribbing and tiebacks are more
>expensive.

The lot is uphill from the street and quite steep, between 1:1 and 2:1,
so placing drilling equipment may be difficult.  I was curious about how
the runoff on a slurry wall is policed; the city probably wouldn't want
all that bentonite going into the storm drain.  
How is a tangent wall or a secant pile wall normally supported?  
Does it act as a sheet pile wall as it is unearthed?
-- 


-GL
www.lod.org