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Re: Water reservoir - joints, wall ties, and alternate pours

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Snap ties with water stoppers should be used for the wall forming.  Also I
would use more than a bond breaker between the walls maybe 1 to 2 inches.

Ibrahim

From: "Kevin Below" <kevin.below(--nospam--at)sympatico.ca>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: Water reservoir - joints, wall ties, and alternate pours
Date: Thu, 14 Mar 2002 17:47:31 -0500

I am designing my first water-retaining structure - a series of 3
underground rectangular tamks, each 20m x 20m x 2.5m deep with 355mm
(14") wall thickness. We have 60 degrees Celsius range of temperature
here in Quebec.
The total length is thus 60m, which is a long way to go without joints.
But I would like to avoid joints like the plague, so I have elected to
use a separate structure for each tank.  So I have a double-wall between
the tanks, with the intention to pour the walls of one tank, apply a
bond-breaker on the face of the common wall, and then pour the second
tank, and so on.
I don't like it, because it complicates the wall ties for the second
wall of the double-wall section.  And then I have to cover the joint
with flashing to keep out the water in our freeze-thaw climate.  But the
experts in my books seem to agree that no joint is a good joint,... well
maybe construction joints are a necessary evil and can be done well.

What do you think?  Is it better to separate the tanks as I have
proposed, or to simplify the construction and add a joint or two ?

What do you do with the wall ties ?  Do you use conical ends, and patch
the holes?  Will non-shrink grout do the trick?

What about pouring the wall in alternate sections, leaving short
sections to infill after a week or two?  Is it worth it?

I have been researching this and doing my calcs for 3 days now, and I
have accumulated a lot of notes from my references, but they can't
answer everything I guess...
I have heard horror stories of engineers in court because of leaky
tanks, so I am very wary.  One reference I use is in a chapter on
water-retaining structures by B.P. Hughes at the University of
Birmingham.  He mentions the importance of limiting crack widths to
0.1mm (0.004"), which usually controls the design.  And so it does in
this case.  Steel stresses are way down at about 50 MPa (7,000 psi).
Interesting.  It's very different from buildings.

Kevin Below
Génécor inc., experts-conseils



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