TM 5-818-1 / AFM 88-3, Chap. 7
Table 4-4. Surface Geophysical Methods
Name of Method
Procedure or Principle Utilized
Based on time required for seismic waves to
Utilized to determine depth to rock or other
travel from source of blast to point on ground
lower stratum substantially different in wave
surface, as measured by geophones spaced at
velocity than the overlying material. Used only
where wave velocity in successive layers
seismic waves at the interface between
becomes greater with depth. Used to determine
different strata gives a pattern of arrival times
rock type, rock and soil stratification, depth of
vs distance at a line of geophones.
weathered zone, etc.
The travel time of transverse or shear waves
Velocity of wave travel end natural period of
generated by a mechanical vibrator consisting
vibration gives some indication of soil type.
of a pair of eccentrically weighted disks is
Travel time plotted as a function of distance
indicates depths or thicknesses of surface
specific distances from the vibrator.
strata. Useful in determining dynamic modulus
of subgrade reaction and obtaining information
on the natural period of vibration for design of
foundations of vibrating structures.
Used to determine horizontal extent and depth
Based on the difference in electrical
of subsurface strata. Principal applications for
investigating foundations of dams and other
subsoils at various depths is determined by
large structures, particularly in exploring
measuring the potential drop and current
granular river channel deposits or bedrock
flowing between two current and two potential
surfaces, sources of construction material,
electrodes from a battery source. Rerirstivity
potential infiltration and seepage zones, and in
Based on the determination of the ratio of
indication of vertical or steeply inclined
potential drops between three potential
electrodes as a function of the current imposed
Drop in potential
More susceptible than
on two current electrodes.
minor irregularities in surface soils.
The time of travel of sound waves reflected
exploration to determine position of mud line
from the mud line beneath a body of water and
and depth to hard stratum underlying mud.
a lower rock surface is computed by
Method has been used in water depths greater
predetermining the velocity of sound in the
than 100 feet with penetrations of 850 feet to
Excellent display of subsurface
stratification. Used most efficiently in water
depths up to 50 feet with penetrations of
additional 350 feet to bedrock.
Instrumentation for methods listed above currently available at WES. May be furnished as a service to Districts
and Divisions on request. Table adapted from "Design Manual, Soil Mechanics, Foundations, and Earth
Structures, " Department of the Navy. Bureau of Yards and Docks.