30 June 2001
investigations in the areas of proposed pavement should include measurements of in-place water
content, density, and strength to ascertain the presence of weak areas and soft layers in the subsoil.
e. Borrow Areas. Where material is to be borrowed, borings should be made in these areas to a
depth of 0.6 to 1.2 meters (2 to 4 feet) below the anticipated depth of borrow. One boring should be
made for each 930 square meters (10,000 square feet) with a minimum of three borings per borrow
area. Samples from the borings should be classified and tested for water content, density, and strength.
f. Environmental Hazards. When conducting subsurface investigations, hazardous or toxic waste
material may be located, and appropriate environmental actions will have to be taken. This may be true
around fueling areas particularly if replacing an existing fueling apron where fuel has leaked through the
pavement and contaminated the soil. There may also be buried materials that have to be dealt with in
3. SELECT MATERIAL AND SUBBASE FOR FLEXIBLE PAVEMENTS. Areas within the airfield site
or within a reasonable haul distance from the site should be explored for possible sources of select
material and subbase. Exploration procedures similar to those described for subgrades should be used.
Test pits or large auger borings are required to obtain representative samples of gravelly materials.
4. BASE COURSES, DRAINAGE LAYERS, SEPARATION LAYERS, CONCRETE AND
BITUMINOUS CONCRETE. Since these pavement layers are generally constructed using crushed and
processed materials, a survey should be made of existing sources plus other possible sources in the
general area. Significant savings may be made by developing possible quarry sites near the airfield
location. This is particularly important in remote areas where no commercial producers are operating
and in areas where commercial production is limited in quantity.
5. OTHER CONSTRUCTION MATERIALS. The availability and quality of bituminous materials and
portland cement should be determined. The availability and type of lime and fly ash will also aid in the
evaluation and applicability of stabilized layers. This information will be helpful in developing designs
and alerting designers to local conditions and shortages.
6. SOIL CLASSIFICATION. All soils will be classified in accordance with the unified soil classification
system (USCS) as given in American Society for Testing and Materials (ASTM) D 2487. Sufficient
investigations will be performed at a particular site so that all soils to be used or removed during
construction can be described in accordance with the USCS plus any additional description considered
necessary. When classifying soils, be alert to the presence of problem soils such as:
a. Clays that Lose Strength When Remolded. The types of clays that show a decrease in strength
when remolded are generally in the CH and OH groups. They are clays that have been consolidated to
a very high degree, either under an overburden load or by alternate cycles of wetting and drying, or that
have by other means developed a definite structure. They have a high strength in the undisturbed state.
Scarifying, reworking, and rolling these soils in cut areas may produce a lower bearing value than that of
the undisturbed soils.
b. Soils that Become "Quick" When Molded. Some soils deposits such as silts and very fine sands,
(predominantly in classifications ML, SM, and SC) when compacted in the presence of a high water
table, will pump water to the surface and become "quick" or "spongy" with a loss of practically all bearing
value. The condition can also develop in most silts and poorly drained very fine sands if these materials
are compacted at a moisture content higher than optimum. This is because compaction reduces the air
voids so that the available water fills practically all the void space.