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Re: Check for Floatation

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I have designed many structures for floatation here in the swamps of
Louisiana. It is true that the soil will fail at some angle(depending on the
soil type). You will also have to overcome soil cohesion in order to float
the tank. However, without geotechnical input, I would not use either. It
should be pointed out that even using the vertical column of soil above the
lip of the tank means that the lip can withstand the load as a cantilever.
Otherwise it will bend and you no longer have the column of soil resisting
uplift.

Randy Russ, P.E.
Russ Engineering Group, Inc.
Baton Rouge, La.
-----Original Message-----
From: RajSTC(--nospam--at)aol.com <RajSTC(--nospam--at)aol.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Tuesday, August 15, 2000 4:31 AM
Subject: Check for Floatation


>I am evaluating the adequacy of a, buried, steel storm shelter manufactured
>by a local steel fabrication shop.  In order to pass the FEMA approval
>criteria, the structure has to be checked for floatation assuming that the
>water table can rise up to the ground level.  For a box, L'XW'XH', the
>buoyancy is 62.4LWH.  The weight of the steel structure is very small in
>comparison to the buoyancy.  Additional weight has to come from soil weight
>on the extended portions of the bottom plate.  For the purposes of further
>discussions, assume that the bottom plate extends 2' beyond the face of the
>walls.
>
>For estimating the weight of soil on the extended plate, should the soil be
>limited to 2' wide column?  It seems to me that the failure of soil will be
>in the form of a wedge, the wedge being bounded by the vertical wall of the
>structure, the 2' projection of the bottom plate, existing ground surface
and
>an inclined line emanating from the edge of the extended plate.  The
inclined
>line could be assumed to be at 60 deg. from the horizontal.
>
>No site specific soil reports available.  The structure will be installed
>anywhere in Oklahoma and adjoining states.  I will put a disclaimer on the
>drawing to exclude sites that may have expansive clays, silts etc.
>
>Any thoughts?
>
>P. Rajendran
>Service & Technology Corporation
>105 SW Penn
>Bartlesville, OK 74003
>Ph: 918 336 8161  FAX: 918 336 8265
>
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