TM 5-818-1 / AFM 88-3, Chap. 7
entiating between sand and clays. Both methods require
4-8.
Borehole surveying.
distinct differences in properties of foundation strata
a. Downhole surveying devices can be used in
materials to be effective. The resistivity method requires
correlating subsurface soil and rock stratification and in
a high-resistivity contrast between materials being
providing quantitative engineering parameters, such as
located. The seismic method requires that the contrast
porosity, density, water content, and moduli. Once a
in wave transmission velocities be high and that any
boring has been made, the cost of using these tools in
underlying stratum transmit waves at a higher velocity
the borehole is relatively modest. Different devices
(more dense) than the overlying stratum.
Some
currently in use are summarized in table 4-5.
difficulties arise in the use of the seismic method if the
surface terrain and/or layer interfaces are steeply sloping
b. These devices can allow cost savings to be
or irregular instead of relatively horizontal and smooth.
made in the exploration program without lessening the
quality of the information obtained.
4-12
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