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Re: Underground Tanks

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Gentlemen,
 
        I have chosen not to respond to this line earlier for two reasons: I do not have a great deal of knowledge of your codes; and I am not really the world's greatest expert in seismic design.
 
        That said, I do have some thoughts that may or may not be useful.
 
1.)  Codes generally are focused on personal safety rather than on preservation of assets, therefore, any information you do find in the literature may be less than ideal for your purposes.
 
2.)  The intended purpose of storing the water may be important.  If it's for fire protection, for example, you need to preserve the WATER not the tank.  Backfilling with clay and/or using some type of poly or other water resistant membrane should preserve the water for several hours or days.  Contaminated or dirty water will still work just fine for fighting fire but not for many other purposes.
 
3.)  Using multiple shorter tanks may be a useful idea.  Two or three separate shorter tanks should be much less prone to complete failure than one longer tank.
 
        I don't know if anything I've written above is useful.  If it is you're welcome to it.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Friday, March 23, 2012 10:21 AM
Subject: RE: Underground Tanks

Tim,
This is a poorly defined area of study.  I would suggest that you start with the Foundation Engineering Handbook by Winterkorn and Fang, Chapter 23.  That will give you some of the basics.  Then I would suggest that you look at 2009 NEHRP Recommended Seismic Provisions, page 354, "Seismic Lateral Earth Pressures".   But this will still not address your particular condition (which is generally ignored by the industry).  Another good resource is from the DOE "Seismic Design and Evaluation Guidelines for The Department of Energy High-Level Waste Storage Tanks and Appurtenances".  One of the authors is Dr. Anestis Veletsos.  He is at Rice and well respected in the tank industry. 
 
The best approach would be to require an analysis by an independent consultant such as:
 

Tank Industry Consultants

7740 West New York Street

Indianapolis, IN 46214

Voice: 317-271-3100
 
I contend that seismic on buried tanks is generally ignored because the contention for seismic is that the entire soil mass moves in unison and does not impose an unbalanced load on the walls of the tank until the tank gets very large.  And "very large" is not defined.  You will still get impulsive and convective fluid forces, but they will not come close to the passive soil pressures. 
 
Regards, Harold Sprague
 
> Date: Wed, 21 Mar 2012 14:35:13 -0700
> Subject: Re: Underground Tanks
> From: paul.blomberg(--nospam--at)gmail.com
> To: seaint(--nospam--at)seaint.org
>
> I think you need to define the loading conditions and design criteria.
> AWWA has it's own standards that address tank design.
>
> To get an idea if seismic soil design kicks in you can go to the IBC
> and ASCE 7 and see if the tank falls under Seismic Design Category D
> or higher. Be careful on how you categorize the tank. If it is part
> of the fire water system or supports an essential facility, it is
> categorized as Occ Cat IV.
>
> And do watch buoyancy as it may require a ballast slab if ground water
> table or 100 year flood gets too high. Don't forget compliance to
> NSF-61 if drinking water.
>
> Call a manufacturer in California and ask them how they design for
> seismic soil loading and what information they need in the
> specification to make the bid requirements clear.
>
> Paul.
> Phoenix, AZ
>
> On 3/20/12, Tim Rudolph <TimRudolph(--nospam--at)cox.net> wrote:
> > Good to see the list coming back to life
> >
> > I have a project where we are using fiberglass underground tanks for
> > drinking water. they are cylinders 10 ft diameter x 38 ft long. They are to
> > have 4 ft of dirt cover and are to be HS-20 load rated. Since it is
> > underground I am not sure what part of the CA building code covers the
> > design for seismic forces. It will be built to a AWWA standard. What can I
> > expect the tank mfg to submit for seismic design calculations.
> > Thanks
> > Tim Rudolph PE
> > 949 498-8454
>
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