Soil Exploration - Soil Properties: Testing, Measurement, and Evaluation - page 7

Much of geotechnical engineering practice can be successful only if one has
long experience with which to compare each new problem.
Soil exploration may be thought of as consisting of three steps—
boring, sampling, and testing. Boring refers to drilling or advancing a
hole in the ground, sampling refers to removing soil from the hole, and
testing refers to determining characteristics or properties of the soil.
These three steps appear simple in concept but are quite difficult in good
practice and are discussed in detail in the remainder of this section.
Boring
Some of the more common types of borings are auger borings, test pits ,
and core borings .
An auger (see Figure 2-1) is a screwlike tool used to bore a hole.
Some augers are operated by hand; others are power operated. As the
hole is bored a short distance, the auger may be lifted to remove soil. Re-
moved soil can be used for field classification and laboratory testing, but
it must not be considered as an undisturbed soil sample. It is difficult to
use augers in either very soft clay or coarse sand because the hole tends
to refill when the auger is removed. Also, it may be difficult or impossi-
ble to use an auger below the water table because most saturated soils
will not cling sufficiently to the auger for lifting. Hand augers may be
used for boring to a depth of about 20 ft (6 m); power augers may be used
to bore much deeper and quicker.
Test pits are excavations into the earth that permit a direct, visual
inspection of the soil along the sides of the pit. As depicted in Figure 2-2,
they may be large enough to allow a person to enter them and make in-
spections by viewing the exposed walls, taking color photographs of the
soil in its natural condition, testing in situ , and taking undisturbed sam-
ples. Clearly, the soil strata (including thicknesses and stiffnesses of
strata), texture and grain size of the soil, along with visual classification
of soils, soil moisture content, detection of fissures or cracks in the soil,
and location of groundwater, among others, can be easily and accurately
determined throughout the depth of the test pit. Soil samples can be
Figure 2-1
Auger Boring
Power Earth Auger (Truck Mounted)
Cuttings Carried
to Surface
Continuous Flight Augers in Sections
Cutter Head (Replaceable Teeth)