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|Title:||Rapid subsurface exploration. Report 1, Review of selected geophysical techniques|
|Authors:||Ballard, Robert F.|
Chang, Frank K.
|Publisher:||Soils and Pavements Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: The objective of the study reported herein was to investigate improved or new techniques to extend the depth and resolution capnbility of rapid shallow-depth (less than 500 ft) explorations that would quickly and ec0nomically provide an engineer with accurate information on substrate conditions. This report does not advocate the adoption of a new test technique at the present time. It seeks only to present a discussion of potential improvements in rapid test techniques. The current geophysical techniques for rapidly exploring construction sites and investigating foundations, i.e., electrical resistivity, seismic refraction, and vibratory techniques, are discussed herein. Preliminary results indicate that a study of surface wave phenomena can measurably extend the depth limits of current investigation techniques. Utilizing special recording and interpretation procedures, data were acquired at several test sites and compared with results acquired by more conventional methods. The preliminary results of a Rayleigh-wave dispersion techniqiue have yielded velocities consistently greater at depths of 50 ft or more than the conventional vibratory method. These apparent differences have not yet been fully resolved, but indications are that these discrepancies are possibly the result of wave distortions caused by interfering multiple wave trains or possibly differences in stress conditions at the source. These wave patterns and resultant group velocities will be the subject of future study.
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