REGIONAL STUDY. Site selection requires a regional study to determine
the geological origin of the soils and potential for seismic activity that
must be considered in foundation design.
Geological Factors. A preliminary study must be made of the
geological origin of the soils in the various regions under consideration.
The principal soil deposits can be classified as residual, sedimentary,
alluvial, aeolian and glacial. Generally residual sands and gravels, some
alluvial deposits, and glacial tills will be the most favorable soil
conditions for foundations.
Seismic Activity. Avoid, if at all possible, locating hyperbaric
facilities in seismic zone 4. (See NAVFAC P-355 for a description of seismic
zones.) Where it is necessary to locate a facility in either seismic zone 3
or 4, particular attention must be paid to the location and character of
faults, topography, the potential for tsunamis, bedrock depth and type, and
the potential for soil liquefaction. A study of the seismicity of the site
including identification of known faults within the immediate region must be
included in the regional study.
LOCAL STUDY. Evaluation of potential sites within the region must be
based on the geology and soil conditions of each site. If possible, sites
underlain by loose saturated sands and silts, soft compressible or organic
soils, and expansive soils must be avoided.
Previous Investigations. Soils maps, geological maps, and previous
subsurface investigations will provide local data.
A qualified geotechnical
engineer should screen potential sites for those having the most favorable
soil conditions. The available information on soil type and consistency,
groundwater elevations, potential excavation or slope stability problems, and
predominant foundation type in the area must be reviewed.
Seismic Considerations. Geological and subsurface investigation
must be conducted to assure that the site is not located on or near a fault.
In seismically active areas, potential for ground rupture, vibration
settlements and soil liquefaction must be evaluated by a geotechnical