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RE: Retaining wall drains

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Will,
I use drains.  I use 4" diameter PVC drains at 8'-0" o.c.  I also backfill 
with open graded aggregate (crushed rock or gravel).  The open graded 
aggregate should have no fines and can be anything from 3/8" to 1").  The 
open graded aggregate is wrapped with filter fabric to limit the amount of 
fines that can get to the drains.  I generally have a cap of soil on the 
top for planting.  I protect the drains with a #10 galvanized mesh to keep 
the drains open.

It is also easy to consolidate the aggregate with a walk behind vibrating 
compactor.  This puts a lot less pressure on the wall as opposed to 
compacting a clay soil material.

Eventually the drains will fill with fines, but that will be a long, long 
time from now.  I am old enough now to have seen buildings that I designed 
in the early 1980's be demolished to make way for some other project. 
.....oh well.

Regards, Harold Sprague

> From: gtg740p(--nospam--at)gmail.com
> Date: Sat, 8 Dec 2012 11:47:27 -0500
> Subject: [SEAINT-SEAOSC] Retaining wall drains
> To: seaint-seaosc(--nospam--at)mail-list.com
> 
> I wanted to see how many of you rely on drains behind retaining walls for
> your wall design versus ignoring them. I understand these drains can end 
> up failing with time. The geotech reports I get are often based on soil
> pressures assuming a drained condition behind the wall.
> 
> Will H

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