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Re: French drain installation

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Around here our walls are usually drained in one of 3 ways:
1. As described by Harold, except that the drain rock/filter fabric extends to within a foot of the top of the wall & capped by an "impervious earth plug" (fat chance--the landscaper usually uses good planting soil).
2.  Class II  base in place of the drain rock/filter fabric
3.  Miradrain, or equal, in place of the drain rock/filter fabric

The perf. pipe should slope but it often doesn't happen (or it's placed on a  sloped bed of drain rock--useless).  This drainage system must be completely separate from the surface drainage system. If you really want a waterproof wall, add Xypex to the concrete, in addition to the normal waterproofing membrane.
C. Utzman, P.E.
P.S. If there's much flow, these systems usually plug up eventually (roots or fines or both).
P.P.S. Harold-I've always called this a "french drain", could you explain your nomenclature.

Cratylus Consulting Group wrote:
Good point!
A "french drain" is not a "back drain" or wall drain.

Steven A.
Los Angeles

"Sprague, Harold O." wrote:

  
Desi,
I am a little confused.  Are you installing a French drain or just providing
a continuous perimeter wall drain?

There is no standard of care, but I can offer what I have done in the past
for a continuous perimeter wall drain.
I provide filter fabric in the base of the excavation and use 3/8" open
graded clean crushed rock at the base lay the pipe at (1/4" ideal 1/8" after
the war) per foot.  I use enough filter fabric to wrap all of the crushed
rock.  After the pipe is placed I back fill with more crushed rock to
provide a minimum of 12" of rock around the pipe.  I then finish wrapping
the crushed rock in filter fabric and lap the fabric over the crushed rock.
This wraps the entire crushed rock in filer fabric.  If you just wrap the
pipe, the filter fabric has much less surface area and will seal with fines
rather quickly.

If you are indeed considering a French drain, you should run your perimeter
wall drain to the French drain.  The size of the French drain and location
will depend on the water table and the percolation rate of the soil.  I
would avoid making the perimeter wall drain the French drain. You will wind
up with a pool of water along your wall.

If indeed you have a retaining wall, just run your continuous wall drain to
weeps placed at about 10' centers.

Regards,
Harold O. Sprague

-----Original Message-----
From: djkiss55(--nospam--at)juno.com [mailto:djkiss55(--nospam--at)juno.com]
Sent: Monday, July 07, 2003 1:13 PM
To: seaint(--nospam--at)seaint.org
Subject: French drain installation

Any response to these issues is gratly appreciated.

What is the standard of care for installing a 4" dia. french drain along a
70 foot-long by 9 foot high masonry retaining wall? Are there any gravel or
crushed rock specific requirements? What is the minimum slope required by
the standard of care? Is a 1/4" slope appropriate?

Thank you in advance.

Desi J. Kiss, MS, PE
Phone: 949/458-9169
E-mail: djkiss55(--nospam--at)juno.com

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