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This report details a research effort initiated in 1974 to assess the state of the art in geophysical cavity detection and delineation methodology and to develop new methods for application to cavity detection and delineation. The report presents results from field studies at the Medford Cave site, including site geology, topographic survey, drilling program, magnetic and microgravimetric surveys, and correlation of geophysical results with known site geology.
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D-A124 574 CAVITYMICROGRAYIMETRIC DETECTION (^) AND AND (^) M..CU)DELINEATION ARMY (^) ENGINEER RESEARCH (^) WATERWHYSREPORT 1 1/ EXPERIMENT STATION VICKSBURG MS GEOTE. D K BUTLER UNCLASSIFIED MAR 82 NES/TR/GL-S3i- F/G 8/7 N
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Title Author Report (^) 1: Microgravimetric and Magnetic Surveys: Medford Cave Dwain K. Butler Site, Florida 0 Report 2: Seismic Methodology: Medford Cave Site, Florida Joseph R. Curro, Jr. Report 3: Acoustic Resonance and Self-Potential Applications: Stafford S. Cooper Medford Cave and Manatee Springs Sites, Florida Report 4: Microgravimetric Survey: Manatee Springs Site, Florida Dwain K. Butler, Charlie B. Whitten, Fred L. Smith Report 5: Electromagnetic (Radar) Techniques Applied to Robert F. Ballard, Jr. Cavity Detection
Destroy this repnrt when no longer needed. Do not return it 0 to the originator.
The findings in this report are not to be construed as an official Department of the Army position unless so desig- nated by other authorized documents.
0 The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement^ or approval of the use of such commercial products.
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Unclassified SECURITY CLASSIFICATION OF THIS PAGE (Ian. Des Entered)_________________
I. _REPORT NUMBER GF-OVTACC ESSION NO. S. RECIPIENT'S CATALOG NUMBER Technical (^) Report (^) GL-83-1 (^) JA- (^) Al-,2V' (^) s-;?Y_
4. TITLE (mid Subtitle) S. TYPE OF REPORT & PERIOD COVERED CAVITY DETECTION AND DELINEATION RESEARCH: Report 1, !ICROGRAVIMETRIC^ AND^ MAGNETIC^ SURVEYS:^ Report^1 of^ a^ series MEDFORD CAVE SITE, FLORIDA S.^ PERFORMING^ ORG.^ REPORT^ NUMBER 7. AUTHOR() S. CONTRACT OR GRANT NUMBER(&)* Dwain K. Butler 3. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT PROJECT. TASK U. S. Army Engineer Waterways^ Experiment^ Station^ AREA^ &^ WORK^ UNIT^ NUMBERS Geotechnical Laboratory P. o. Box 631, Vicksburg, Miss. 39180 CWIS Work Unit No. 31150 It. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE Office, Chief of Engineers, U. S. Army March 1983 Washington, D. C. 20314 13. NUMBER (^) OF PAGES **136
Available from National Technical Information Service, 5285 Port Royal Road, Springfield, Va. 22151.
Cavities (Underground) Medford Cave Geophysical exploration Subsurface exploration Gravimetric surveys
20 ABSTRACT (Cimotbiuse eves eebb N^ nvesomy^ and^ Ideniff^ by^ block^ nuber) "'iThis report reviews the scope of a research effort initiated in 1974 at the U. S. Army Engineer Waterways Experiment Station with^ the^ objectives^ of (a) assessing the state of the art in geophysical cavity detection and delinea- tion methodology and (b) developing new methods^ and^ improving^ or^ adapting^ old methods for'application to cavity detection and delineation. Two field test sites were selefted: (a)^ the^ Mledford^ Cave^ site^ with^ a^ relatively^ shallow (10- to 50-ft-deep) air-filled cavity system and (b) the Manatee Springs site (Continued)
SECUITY CLASSIFICATION OF THIS PAGE (Mmon Date Entered)
L This investigation was performed by personnel of the Earthquake Engineering and Geophysics Division (EEGD), Geotechnical Laboratory (GL),. - U. S. Army Engineer Waterways Experiment Station (WES), for the Office, Chief of Engineers (OCE), U. S. Army, during the period May 1979 to
"Remote Delineation of Cavities and Discontinuities." This report was prepared by Mr. Dwain K. Butler, EEGD. The field work described in this report was performed by Messrs. Butler, Joseph R. Curro, Jr., and Rodney N. Walters, EEGD, and was closely coordinated with other studies at this site conducted under this same work unit, work carried out under an In-House Laboratory Independent Research (ILIR) Project, "Microgravimetric Techniques for Geotechnical Applica- tion," and the Project 4A161102AT22, Work Unit 002/Q6, "Analytical and Data Processing Techniques for Interpretation of Geophysical Properties." Assistance with field programs at the Medford (^) Cave site was pro- "
Dr. Robert Ho of the Florida Department of Transportation, Gainesville, Fla. Assistance of personnel of Southwest Research Institute, San Antonio, Tex., in obtaining cavity and site maps, supplying information about their previous work at the site, and other assistance throughout this investigation is gratefully acknowledged. Mr. William D. Reves, , Ocala, Fla., served as geological consultant for the work, assisted in core logging, and prepared Appendix A of this report. Special acknowledgement is given to Professor Robert Neumann and. ' the Compagnie Generale de Geophysique (CGG), Massy, France. Profes- sor Neumann provided encouragement and assistance throughout the program. In July 1979, Mr. Butler visited Professor Neumann with data from the :" microgravity survey at the Medford site. Professor Neumann, Mr. Jacques Regnaudin, and other colleagues at CGG assisted in the data processing and preparation of anomaly maps and documented their contributions in a letter report under Contract Agreement DAJA 37-79-M-0027. A Sharpe Magnetometer, Model MF1-100, was obtained on loan from 1 0
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the Department of Geophysics, Texas A&M University, for use during this work. Also, a LaCoste and Romberg Gravimeter, Model D4, was loaned to WES by the U. S. Army Engineer District, Seattle. The work was performed under the direct supervision of Dr. A. G. Franklin, Chief, EEGD, and the general supervision of Dr. W. F. Marcuson III, Chief, GL. Mr. Paul Fisher was the OCE Point of Contact
the Work Unit. Commanders and Directors of WES during the performance of this work and publication of this report were COL Nelson P. Conover, CE, and COL Tilford C. Creel, CE. Mr. Fred R. Brown was Technical Director.
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N MEDFORD (^) CAVE SITE, FLORIDA
Background
1. In 1974, a research program, funded by the Office, Chief of L Engineers (OCE), U. S. Army, (^) was initiated at the U. S. Army Engineer Waterways Experiment Station (^) (WES) with the objectives of assessing the state of the art in geophysical cavity detection and delineation methodology and developing new methods and improving or adapting (^) old
5
(4) Neutron. Results of these additional geophysical surveys will be presented (^) in
. subsequent reports in this series.
Purpose
3. The purposes of this investigation (^) were to (a) determine whether surface microgravity and magnetic surveys would indentify anomaly patterns consistent (^) with known cavity geometry, (b) investigate the use of the (^) methods to detect previously unknown cavity or other solu- tion features at the site, and (c) determine (^) size and depth detectabil- ity of solution features and ability of the methods (^) to resolve closely spaced (^) features.
quent (^) reports.
5. Part II of this report discusses (^) the Medford Cave site, in- cluding area geology, site geology, the known cave (^) system, and the site drilling program. Part III describes the magnetic (^) survey and results, and Part IV describes the microgravimetric (^) survey and results. Correla- h tions of the (^) microgravimetric and magnetic results with each other and with known geology and the (^) results of the site drilling program are pre- sented in Part V. Part VI contains the summary and (^) conclusions.
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Location O
6. Medford Cave (or Medford's Cave) is located in Marion County, Fla., about 1 mile south of Reddick. The location of Medford Cave as well as the Manatee Springs test site is shown in Figure 1. A portion S of the U. S. Geological Survey Reddick Quadrangle (1968) is shown in Figure 2, with the approximate site location indicated. Figure 3 is an aerial photograph of the Medford Cave site (circa 1974); the main en- trance to the cave system is hidden in the cluster of trees in the center of the (^) photograph.
History of Site Use
7. The Medford Cave is located on land formerly part of the Med- ford Plantation. Apparently, the cave system has been known at least since the time the plantation was in operation, and stories are told of people being lost in the cave and of people entering and then emerging 4 at sinkholes 1 and 2 miles away. A steel ladder was installed in the primary entrance (Figure 4) reportedly in the 1940's, and the cave has been a popular excursion site for people in the vicinity and for speleological groups. The land around the site has been used for both vegetable farming and livestock grazing. 8. Scientific use of the site began in the early 1970's when the Southwest Research Institute (SwRI), San Antonio, Tex., with the assis- tance of the Florida Department of Transportation, Gainesville, selected - the site for evaluation of three geophysical methods for cavity/tunnel detection (Fountain, Herzig,^ and^ Owen^ 1975).^ In^ addition^ to^ mapping^ the cavity system, the investigators conducted a standard gravity survey, a
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to detection (^) depths shallower than about 15 ft (4.5 m). The gravity survey results did not correlate very well with the known cavity (^) system, indicating anomalies which were close but (^) not directly over the largest
site, with each boring in (^) an area where at least two of the methods in- dicated anomalies. However, all three (^) borings encountered only solid material to depths of 32 to (^) 52 ft (9.8 to 15.8 m).
9. WES personnel visited the site (^) in early 1979 on a tour of several candidate sites for use in the cavity detection (^) and delineation "- research program. (^) Several factors contributed to the selection of the Medford Cave as the first of two test sites planned under (^) the program: , *- a. A cavity (^) system almost entirely air-filled. b. Easy site access. c. Gently sloping topography.
e. Known (^) portion of cavity system shallow, but with a good range of cavity depths. f. Cavity system presumably well-mapped. " Available results of previous geophysical tests at the site. (^) r The Florida Department of Transportation agreed to obtain site (^) use approval and to assist in the (^) test program, which began in May 1979.
Geology
Area geology
10. The Medford Cave site is situated near the east-central flank of the (^) Ocala Uplift, a northwest-southeast trending "anticlinal struc- ture" (Faulkner 1970). Although (^) the Ocala Uplift is apparently bounded by faults, the area (^) is considered tectonically stable. The primary active geological process affecting the area is solutioning of (^) lime- stones and dolomites td produce karst topography (^) with little surface drainage, development of subsurface (^) cavities, sinkhole formation, etc. Local relief in the area is about (^) 110 ft (34 m) and consists of gently
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rolling hills and valleys. Generally the hills are capped by only a^ few feet of sands and clays over limestone.^ The^ shallow^ depth^ to^ top^ of limestone has resulted in many limestone quarries in the^ area.^ Exten- sive cave systems with^ attendant^ sinkhole^ formation^ are^ commonly^ asso- ciated with the hills and higher limestone elevations.^ The^ general^ geol- ogy of the area^ and^ of^ the^ Medford^ Cave^ site^ in^ particular^ is^ covered in Appendix A. Site geology
11. The general sequence of^ materials^ at^ the^ Medford^ Cave^ site^ is sand (with silt, clay, and organic material), clay^ (may^ or^ may^ not^ be present at a given location), and limestone. Typically, the^ sand^ ranges from nearly 0 to about 4 ft in thickness. The^ clay^ (residual)^ occurs primarly in pockets in the limestone surface. Figure 5 shows a cut^ at^ a - r° - ,-
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Figure 5. Vertical^ cut^ showing^ limestone^ pinnacles^ and clay pockets in quarry near^ the^ Medford^ Cave^ site nearby limestone quarry^ (located^ approximately^^1 mile^ east^ of^ the^ site)^ " showing a pinnacled limestone^ surface^ with^ clay^ filling^ the^ pockets between the pinnacles; the^ top^ of^ the^ limestone^ at^ the^ Medford^ Cave^ site is similarly^ pinnacled^ (shown^ in^ the^ next^ section).^ Two^ limestone
14.
