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|Title:||Earth resistivity and hole-to-hole electromagnetic transmission tests at Medford Cave, Florida|
|Authors:||U.S. Army Engineer Waterways Experiment Station.|
Fountain, Lewis S.
Herzig, Francis X.
|Keywords:||Soil penetration test|
Medford Cave, Florida
|Publisher:||Southwest Research Institute|
Engineer Research and Development Center (U.S.)
|Description:||This Digital Resource was created from scans of the Print Resource.|
Introduction: Requirements for an effective method for detecting and mapping subsurface cavities and other geologic anomalies resulted in two new geophysical systems developed by Southwest Resc3rch Institute under contract to the U.S. Army Mobility Equipment Research and Development Command (MERADCOH), Fort Belvoir, Virginia. The first of these systems, a borehole ground-penetrating VHF electromagnetic probe, was initially developed in experimental for the Bureau of Hines in 1976 and later refined for operational use by the Army for use in overseas environments. The second system is a surface-operated automatic earth resistivity survey system with a digital computer data processing and display capability. The earth resistivity system is designed to operate as a high-resolution surface search and detection capability for use against subversive man-made tunnels. This method has been demonstrated in several field test environments detect subsurface cavity targets having a depth-to-diameter ratio of 10 to 1 and greater. The borehole ground-penetrating electromagnetic system developed for Army use operates as a hole-to-hole transmission system to provide a means of projection imaging of major geologic structures located between the source and receiving drill holes. This method is capable of yielding well resolved information on the approximate size, depth below surface, and position between holes of tunnel cavities. The borehole technique is used primarily for verification of tunnel targets suspected in the earth resistivity surveys. Both of these equipment systems are briefly described in the next section of this report. Waterways Experiment Station (WES) has the requirement to detect and map underground cavities and other geologic anomalies that might cause ground subsidence, leaks or failures in earthen dams, or otherwise influence the engineering properties of the near-surface zone of the ground; The joint interests of WES and HERADCOM in these relatively similar geologic target objectives led to the field demonstration tests reported herein. The test site was Medford Cave, a shallow limestone solution cavity near Reddick, Florida, which offered a complex air-filled cavity target with a large room (approximately 4 x 12 meters) and other smaller openings having average depths in the range of 3 to 9 meters. The field equipment, test site, and test results are presented in this report.
|Appears in Collections:||USACE Collection|
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|Earth-resistivity-and-hole-to-hole-electromagnetic-transmission-tests.pdf||2.83 MB||Adobe PDF|