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RE: drainage behind shoring and permanent wall

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We did a big tie-back wall a couple of years ago with Nicholson
Construction Co.  The wall provides stability for a water plant that is
situated on top of a large hill.  We did the performance spec and
Nicholson did the detailed design.  We also did the Construction
Management on this project, so I got to go out a few times and see what
was going on.  

The geotechnical company who made recommendations for the wall (i.e.,
number and spacing of anchors, tension in the anchors, etc) also made
the recommendations for the drainage system.  They recommended (and we
used) Mirafi drainage fabric between the concrete soldier piles and
behind the concrete facing.  The actual layering from the face of the
soil consisted of the following:  soil, Mirafi drainage fabric with the
cloth side facing the soil, thin plastic sheets, chicken wire and
shotcrete lagging (not structural), and then double reinforcing and a
thick shotcrete facing wall.  The plastic sheet was used to keep the
shotcrete lagging out of the little coned area of the drainage fabric.

At the bottom of the wall, the drainage fabric turned into sort of a
french drain with more gravel and plenty of weep holes through the
concrete to the front of the wall.  We had a blast doing this project
since we don't do many of these tie-back walls.

Hope that helped,  Mike

> -----Original Message-----
> From:	Chris Lillback [SMTP:thedrdirt1(--nospam--at)]
> Sent:	Friday, July 07, 2000 9:41 AM
> To:	seaint(--nospam--at)
> Subject:	drainage behind shoring and permanent wall
> Suppose you have temporary shoring which will be part of permanent
> wall. height 25 to 29 feet. 
> welcome suggestions for drainage behind wall... and placement of same.
> space is confined. Continuous lagging. Width between piles is 6 feet.
> Sand drains? Mirafi drainage material? Should detail be shoring
> engineers responsibility or structural engineer? 
> Retained earth is very cohesive and locally stable. 
> I welcome any comments or sharing of actual experience. 
> Chris Lillback

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