Borrow Areas
When material is to be borrowed from adjacent
areas, make borings carried 2 to 4 feet below the
anticipated depth of borrow in these areas. Classify and
test samples for water content, density, and strength.
Explore areas within a reasonable haul from the site
for possible sources of select material suitable for use
as a subbase. Exploration procedures are similar to those
described for subgrades. You need test pits or large auger
borings drilled with power augers for gravelly materials.
RECOMMENDED PROCEDURES
FOR SOIL SURVEYS
The following guide and step-by-step procedures
will help the military engineer when conducting soil
surveys:
l considerations include soil types, securing of
samples, density and moisture content of soil in place,
drainage characteristics, and depth to groundwater and
bedrock.
l Published information includes geological and
topographic reports with maps and agricultural soil
bulletins with maps. These require careful interpretation
and knowledge of local terms. Aerial photographs used
to predict subsurface conditions and previous
explorations for nearby construction projects are also
useful.
l Field information requires general observation of
road cuts, stream banks, eroded slopes, earth cellars,
mine shafts, and existing pits and quarries. Test holes
may be made with a hand auger or a power auger, if
necessary and available. Test pits are necessary where a
hand auger cannot penetrate or where large samples are
required.
. Local inhabitants, preferably trained observers
such as contractors, engineers, and quarry workers, can
provide valuable information.
Preparation
Planning of the general layout will determine the
extent of the various soil types, vertically and laterally,
within the zone where earthwork may occur. Large cuts
and fills are the most important areas for detailed
exploration.
. Airfield exploration. Place borings at high and
low spots, wherever a soil change is expected and in
transitions from cut to fall. There is no maximum or
minimum spacing requirement between holes; however,
the number of holes must be sufficient to give a
complete and continuous picture of the soil layers
throughout the area of interest. As a general rule, the
number of exploration borings required on a flat terrain
with uniform soil conditions will be less than in a terrain
where the soil conditions change frequently.
Exploration borings should be conducted at the
point of interest and located in a manner to get the
maximum value for each boring. This may require
exploration boring in the centerline as well as edges of
runways or roads, but no specific pattern should be
employed except as perhaps a staggered or offset pattern
to permit the greatest coverage. It is accepted policy to
conduct the exploration borings at the edge of existing
pavements, unless these pavements have failed
completely. In this case, the reason for the failure should
be found.
l Depth exploration. Take a cut section 4 feet
below subgrade, if possible, and a fill section 4 feet
below original ground level, if possible. Effort should
be made to locate the groundwater table.
Procedures
l
l
l
Log the exploration holes or pits.
Locate and number the samples.
Determine the elevation and exact location of
each hole and tie into the site layout.
Technical Soils Report
A good program for soils testing not only requires
that careful and complete tests be performed but also
that the tests be completed as quickly as possible and
that the data be clearly and accurately presented in a
technical soils report. The organization and presentation
of the soils report is highly important. The report must
be well-organized and must be presented in a logical and
concise format with emphasis on technical conclusions.
For further discussion and a suggested outline for a soils
report, you should refer to Materials Testing, NAVFAC
MO-330.
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