FLOOD04542

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Design and Construction of Levees
• Date: 4/16/1979
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EM 1110-2-1913
31 Mar 78

Exploration from the ground surface will generally be adequate for levee
design purposes. Geophysical ground surface exploration can involve:
(1) seismic refraction and (2) electrical resistivity. Information ob-
tained from seismic refraction surveys includes material velocities,
delineation of interfaces between zones of differing velocities, and
the depths to these interfaces. The electrical resistivity survey is
used to locate and define zones of different electrical properties such
as pervious and impervious zones or zones of higher ionic activity such
as clayey strata. Both methods require distinct differences in prop-
erties of foundation strata materials in order to be effective. The
resistivity method requires a high resistivity contrast between mate-
rials being located, while the seismic method requires high contrast in
wave transmission velocities. Furthermore, the seismic method requires
that any underlying stratUIll transmit waves at a higher velocity than the
overlying stratUIll. Difficulties arise in the use of the seismic method
if the surface terrain and/or layer interfaces are steeply sloping or
irregular instead of relatively horizontal and smooth. Therefore, in
order to use these methods, one must be fully aware of what they can and
cannot do. EM 1110-2-1802 (ref. A-3a(3)) describes the use of both
seismic refraction and electrical resistivity. Dobrin (ref. A-5c) is a
valuable, general text on geophysical exploration. Applicable geophys-
ical exploration methods based on operation from the ground surface are
summarized in table 2-4.

c. Recent developments in the use of downhole logging devices have
shown that these tools can be used with success in correlating subsur-
face soil and rock stratification and in providing quantitative engineer-
ing parameters such as porosity, density, water content, and moduli.
They also provide valuable data for interpreting surface geophysical
data. The purpose in using these methods is to allow cost savings to
be made in the exploration program without lessening the quality of the
information obtained. This can be done by reducing the nUIllber of
borings required to determine subsurface stratification and by allowing
sampling to be done only in those zones where samples are necessary for
laboratory testing, thus reducing the nUIllber of undisturbed samples.

Section III. Field Testing

2-11. Preliminary Strength Estimates. It is often desirable to
foundation strengths during Phase 1 of the exploration program.
methods of preliminary appraisal are listed in table 2-5.

estimate
Various

2-12. Vane Shear Tests. Where undisturbed samples are not being ob-
tained or where samples of acceptable quality are difficult to obtain,
in situ vane shear tests may be utilized as a means of obtaining

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