SECTION 3.
FOUNDATION ANALYSIS AND DESIGN
1.
SETTLEMENT. The primary consideration in the design of foundations for
a hyperbaric facility is that of limiting settlement to a tolerable amount.
a.
Initial Settlement. Initial settlement of the foundation is likely
to occur early in the construction phase prior to the time that the pressure
vessel is installed and placed in service. Except in loose sands or gravels,
initial settlements are not usually significant.
b.
Primary Settlement. After the structure is complete and the
pressure vessels installed, primary settlement of the foundation is likely to
occur due to consolidation of soft materials such as silt and clay. The
magnitude of the primary settlement and the period of time over which it
occurs are critical factors in determining the total and differential
settlement between individual footings and the resulting strain which is
induced in the pressure vessel and connected components.
c.
Secondary Settlement. Secondary settlement may occur after
completion of primary settlement and may be significant in soils containing a
high percentage of organic material.
d.
Cyclic Loadings Settlement. Temporary or permanent settlements may
be induced by cyclic loadings such as filling and emptying of wet pot
pressure vessels and movement of heavy equipment on floors supported on a
foundation common to the pressure vessels or common to other components of
the facility.
e.
Vibration Settlement. Vibration settlement may occur in soils
which can be consolidated by vibration such as loose sand and gravel.
Seismic loading, heavy vehicle traffic, or operating machinery may cause the
vibrations.
f.
Water-affected Settlement. Fluctuations in ground water levels,
whether natural or induced through pumping or draining operations, may cause
settlement and must be considered in the settlement evaluation. Lowering of
the ground water table increases the effective soil weight which results in
consolidation of the soil.
2.
SETTLEMENT ANALYSIS. Settlement analysis must be conducted by a
qualified geotechnical engineer using the procedures in NAVFAC DM-7.1,
Chapter 5. No specific limits can be established for the maximum amount of
tolerable settlement. However, for hyperbaric facilities, maximum
differential settlements between individual footings has been determined to
be:
[DELTA]/L < / = 1/1750
where [DELTA] = maximum differential settlement between
adjacent footings
L = spacing between footings
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