Recent National Institute for Occupational Safety and Health Research Using 

Ground Penetrating Radar for Detection of Mine Voids

By 

William D. Monaghan, Michael A. Trevits, Thomas P. Mucho 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Post Office Box 18070 

Pittsburgh, PA 15236 

and 

John Wood 

Target Drilling 

5134 Oak Road 

Jefferson Hills, PA 15025 

Abstract 

We have tested the ability of ground penetrating radar (GPR) to resolve adjacent mine 

workings. The work was conducted at two National Institute for Occupational Safety and 

Health locations – an underground coal mine and an underground limestone mine. The 

objective of our work was to determine if GPR signals could be received from distant 

mine workings. The GPR system was calibrated on underground mine pillars of known 

dimensions using a variety of antennas. The system was then tested at several 

underground locations in an effort to detect an adjacent drift entry; and an adjacent 

abandoned coal mine. As a means of verification, an in-seam horizontal hole was drilled 

from the active coal mine to the abandoned mine to confirm the presence and location of 

the abandoned mine workings. Our results show that in the case of the limestone mine 

the maximum depth of penetration where the mine workings could be resolved was 85 ft; 

and in the case of the coal mine the abandoned mine workings could be resolved at a 

depth of 205 ft. We conclude that it may be possible to utilize GPR for initial 

underground mine studies followed by directional drilling to accurately delineate the 

extent and position of adjacent abandoned mine workings. 

 

Introduction 

On Wednesday, July 24, 2002, miners working in the Quecreek Mine, Somerset County, 

Pennsylvania accidentally cut into the abandoned Saxman No. 2 Mine releasing millions 

of gallons of water into the active workings. The eighteen miners working in the 

Quecreek Mine immediately began an evacuation; however nine miners eventually were 

unable to escape due to high water levels in the mine workings. Over the next 77 hours, 

the dramatic rescue of the trapped miners gripped the nation as technology and ingenuity 

eventually led to a successful outcome (Pittsburgh Post Gazette, 2002). It appears that 

the Quecreek Mine event was seemingly unique, about ten mine inundations of this type 
occur per year based upon a preliminary analysis of this data (MSHA, 2003). Although 

many more mine inundation incidents are reported, some are caused by cutting into 

uncharted gas and oil wells or heavy rains at surface and underground mines. 

As a result of the Quecreek Mine incident, Pennsylvania Governor Mark S. Schweiker 

established the Governor's Commission on Abandoned Mine Voids and Mine Safety to 

investigate and document the hazards posed by abandoned mine voids, in particular the 

flooding of adjacent operating mines, and to make recommendations regarding the 

accurate location of voids and avoidance of other hazards associated with mining 

(Commonwealth of Pennsylvania, 2002). 

The Commission was charged to make recommendations on: 

• The best engineering practices to be used in the design and layout of modern 

mines adjacent to abandoned mine workings. 

• The regulatory policies and permit review procedures for permitting mines 

adjacent to abandoned underground mine workings. 

• The practices and procedures of mine operations in advance of mining to detect 

mine voids. 

• The training of mine workers who operate mines adjacent to underground mine 

workings. 

• The inspection and compliance of the mine operations with the approved mine 

plans and operating requirements. 

• The rescue and response procedures which shall include policies for sharing 

information with families of miners affected by the accident.

One of the Commission’s recommendations was to continue research, development and 

refinement of the various geophysical methods and techniques to enable these techniques 

to be applied separately or in conjunction with drilling techniques to provide more 

positive results pertaining to the location of and definition of mine voids (PA DEP, 

2002). 

The National Institute for Occupational Safety and Health (NIOSH) was created by the 

1970 Occupational Safety and Health Act to ensure safe and healthful conditions for the 

nation’s workers through research, training, and prevention of work-related illnesses and 

injuries. In 1996, the mining health and safety research mission of the former U.S. 

Bureau of Mines (USBM) was transferred to NIOSH. NIOSH has conducted various 

investigations into technologies that were aimed at detecting mine voids under its 

congressional mandate to conduct mining health and safety research, and through its 

history, including that of the USBM. Because of the Quecreek Mine incident, one of 

these technologies, ground penetrating radar (GPR), was tested to determine its ability to 

resolve adjacent mine workings. The work was conducted at two NIOSH locations – an 

underground coal mine and an underground limestone mine. 

NIOSH operates underground test facilities for research aimed at improving the health 

and safety of those working in the mine environment. The Safety Research Coal Mine 
(SRCM) and Experimental Mine complex is a multi-purpose coal mine located near

Pittsburgh, PA (figure 1). Here there are specialized full-scale underground test facilities 

with ancillary underground and surface equipment that provide for realistic testing and

research for newly developed equipment, procedures, and technologies (NIOSH, 2002). 

The Experimental Mine was opened in the early 1900’s and the SRCM became 

operational in the early 1970’s. The SRCM is a room-and-pillar mine layout 

approximately the size of a working section in a commercial coal mine (NIOSH 1998). 

The mine was developed in the Pittsburgh Coalbed and abandoned mines are located 

nearby. The mine opening averages about 14 ft wide and 6.5 ft tall (includes the 

Pittsburgh Coalbed and the overlying drawslate and rider coal). 

The Lake Lynn Laboratory (LLL) is a highly sophisticated underground and surface 

laboratory located about 60 miles southeast of Pittsburgh, PA, and 10 miles northeast of 

Morgantown, WV, where large-scale explosion trials and mine fire research are 

conducted. The underground workings are sized to match those of commercial coal 

mines, thus making them true, full-scale test galleries. Movable bulkheads permit the 

setup of single-entry, triple-entry, and longwall face configurations for experiments 

(NIOSH 1999). LLL occupies more than 400 acres and was developed in the Greenbriar 

Limestone of the Mauch Chunk Formation. It is locally known as the Wymps Gap 

Limestone (also formally known as the “Greenbriar of Pennsylvania”). The units 

exposed are typically gray, hard, and massive with a few interbedded shale units (Shultz, 

1999). LLL was built at an abandoned commercial limestone quarry where underground 

entries 49-ft wide by 33-ft high were developed when surface mining ceased in the late 

1960's. Later, under the auspices of the U.S. Bureau of Mines, 7,545 ft of new 

underground development was constructed using 19.7-ft wide by 6.6-ft high entries 

(figure 2). These entries, in conjunction with the novel use of two explosion-proof 

bulkhead doors that can be positioned to open or close an entry, can be configured to 

simulate modern-day mining, including room-and-pillar and longwall mining (Triebsch 

and Sapko, 1990). 

Objective and Approach 

The objective of the study was to test the capability of GPR to detect adjacent mine 

openings. We approached this problem by using a variety of antennas whose frequency 

spectra produced pulses centered at near 80-, 100-, 200-, 300-, 400-MHz, in two 

geologically different materials (limestone and coal) at the facilities described above. 

The 100-, 200-, 300-, and 400-MHz antennas were enclosed in shielded cases. The 80-

MHz multiple low frequency (MLF) antenna was not enclosed and as such could pick-up 

stray reflections from surfaces near and around the antenna. It was decided to select 

pillars in mine areas where underground structures had not been built to minimize the 

chance of interference reflections (clutter). We also needed to determine the dielectric 

constant, ε, for each material, because ε varies with the velocity (v) of radiowaves in 

these materials: 

ε = (c/v)

2

, 

where c = 3 x 108 m/sec. 
Ground Penetrating Radar 

GPR is a non-invasive geophysical method that uses reflected and backscattered 

electromagnetic waves to image, locate and quantitatively identify changes in electrical 

properties in the subsurface. Its primary feature is a very short pulse, which allows a 

vertical resolution ranging from centimeters to a few meters, depending on bandwidth. 

The first ground penetrating radar survey was performed as early as 1929 (Olhoeft, 1988; 

Stern, 1929, 1930). It was first applied to earth science problems during the 1940’s and 

1950’s for ice sounding and planetary exploration (Evans, 1963; Thompson, 1979; 

Olhoeft, 1988). Geotechnical applications of GPR to rock and soil did not occur until the 

1970’s when the systems became commercially available (Ulriksen, 1980; Olhoeft, 

1988). GPR has applications in archeological, construction, environmental, and 

geological studies where it is most often used to determine the location, lateral continuity, 

and depth of buried objects and geologic strata. 

The system generates an electromagnetic pulse that is transmitted into the ground with an 

antenna that is moved along the surface, generally at a uniform speed and direction. The 

transmitted energy of the pulse is radiated in an elliptical conical pattern roughly 90E

wide in the antenna plane and 60E wide in the perpendicular plane. Whenever there is a 

change in the dielectric constant of the subsurface material, a portion of the pulse energy 

is reflected back to the surface and is detected by the receiving antenna. This reflected 

pulse provides information on the attenuation characteristics (signal strength) associated 

with the subsurface material and the two-way travel time is recorded. 

How well GPR works depends on two electrical properties of the geological materials 

under investigation: dielectric constant (relative dielectric permittivity) and electrical 

conductivity. The dielectric constant affects the velocity of propagation of the radar 

pulse. The dielectric constant ranges from 1 for air (fastest propagation) to 81 for water 

(slowest propagation). In rocks and minerals, dielectric properties are primarily a 

function of mineralogy, porosity, water saturation, frequency, and depending on the 

lithology, component geometries, and electrochemical interactions (Martinez, 2001; 

Knight, 1990; Knoll, 1996). Variations in each of these parameters can significantly 

change bulk dielectric constants (Martinez, 2001). The greater the difference in dielectric 

constant between two materials, the stronger the reflected pulse energy becomes. The 

electrical conductivity controls the depth of pulse penetration. The lower the 

conductivity of the material, the deeper the pulse can penetrate. Conductivity is 

controlled by the water, mineral, and clay content in the subsurface. The depth of 

penetration of the pulse also depends on the antenna frequency. Higher frequency 

antennas (e.g., 1200 MHz) provide high resolution, but shallow depths of penetration; 

conversely, lower frequency antennas (e.g., 80-MHz) have low resolution, but can detect 

significantly deeper targets. 
SIR-2 System 

The equipment used to conduct the ground penetrating radar surveys was a GSSI SIR®

System 2 (SIR-2) Model No. DC-2 control unit built by Geophysical Survey Systems, 

Inc.1

 The SIR-2 is a lightweight, portable, general-purpose radar system (figures 3-6) and 

is available as an intrinsically safe unit. The reflected pulse is processed by the control 

unit and the data are displayed on the monitor and stored on an internal hard disk. The 

output display can be (1) a single wiggle trace (analogous to an oscilloscope trace), (2) a 

waterfall plot of the wiggle traces, or (3) a multicolored line scan in which the reflected 

signal amplitudes are represented by various colors according to a user-selected color 

look-up table. The data can also be printed via an external printer. 

The two-way travel time is determined by measuring the time interval between the start 

of the transmit pulse and start of the received reflected signal. The amplitude of the 

reflected signal is influenced by the size and geometry of the target, the signal attenuation 

characteristics of the geological materials, and the total distance that the pulse has to 

travel. 

Calibration Testing at LLL 

At the LLL site, a test pillar was selected that was located between the first and second 

cross-cuts of the A and B Drifts. The width of the test pillar was 38 ft and the length was 

67 ft. Calibration tests were conducted at the midpoint of the pillar along its length and 

width. The tests included installing the antenna about 6 inches above the mine floor and 

pointing it towards the other end of the pillar. The GPR system was then operated in an 

attempt to detect the opening on the other side of the pillar. Table 1 shows the SIR-2 

System set-up used for each antenna. Deep scan standard set-up parameters were used 

for each antenna. The values shown in the table, with the exception of the vertical high 

and low pass filter settings, are standard default values. Adjustments to the vertical low 

pass filter settings were made to eliminate high frequency noise (snow) from the data. 

Adjustments to vertical high pass filter settings were made to eliminate low frequency 

noise (tilt) from the data (GSSI, 1994). 

At the onset of calibration testing, we used published dielectric constant values for 

limestone (range 5.5 - 8) (GSSI, 1994). We also examined the perimeter of each 

calibration pillar for obvious signs of geologic anomalies, and none were observed. 

During the tests, the dielectric constant was adjusted in the SIR-2 unit until the arrival 

time of the reflected signal (expressed in term of depth) approximated the dimension of 

the calibration pillar. As a result of the tests, a dielectric constant of 6.0 was established 

for the limestone at the LLL. The resulting radar records were analyzed using GSSI’s 

Radar Data Analyzer for Windows NT (RADAN) software1

. This package allows the 

user to operate in the Windows environment with application-specific modules. Figure 7 

shows examples of the interpreted radar records and the observed anomalies for the 

calibration tests. 

 

1

 Mention of specific product or trade name does not imply endorsement by NIOSH. 
Table 1. SIR-2 System set-up used for GPR scans at the LLL. 

Parameter 

Setting for 

100 MHz

Antenna 

Setting for 

200 MHz

Antenna 

Setting for 

300 MHz

Antenna 

Setting for 

400 MHz

Antenna 

Setting for 

80 MHz

(MLF)

Antenna 

Data collection mode Continuous Continuous Continuous Continuous Continuous

Range, ns Varied1 Varied2 Varied2 Varied3 Varied3

Samples per scan Varied4 1024 512 512 512

Resolution, bits 16 16 16 8 16

Number of gain points 4 5 5 5 4

Vertical high pass filter, MHz Varied5 30 30 30 25

Vertical low pass filter, MHz 200 400 1000 800 200

Scans per second 16 32 32 32 32

Horizontal smoothing, scans 0 5 5 4 0

Transmit rate, KHz 64 64 64 64 32

Dielectric constant 6 6 6 6 6

1. Varied from 200 to 1600 ns. 

2. Varied from 300 to 1300 ns. 

3. Varied from 600 to 1000 ns. 

4. Varied from 512 to 2048. 

5. Varied from 15 to 25. 

Calibration Testing at SRCM 

At the SRCM, two underground sites were selected. The first site was located in deadend cut No. 16 Room of the C-Butt entry. Here, two calibration tests were performed, 

parallel to the coalbed’s dominant joint set (face cleat, also known as the main or master 

cleat) and the subdominant joint set (butt cleat, also known as the cross or board cleat) 

(McCullogh, 1974). In the Pittsburgh Coalbed, the face cleat is well developed, 

exhibiting larger more continuous fracture surfaces. The butt cleat trends approximately 

perpendicular to the face cleat and is much less continuous and frequently terminates 

against the face cleat (McCullogh, 1976). 

Once the locations were selected, the tests were conducted in the same manner as the 

tests at the LLL. The width of the pillar where the antenna was oriented parallel to the 

butt cleat (station A) was 47 ft (figure 8) and the width of the pillar where the antenna 

was oriented parallel to the face cleat (station B) was 42 ft (figure 9). A second test site 

(station C) was selected where the pillar length was 76 ft (figure 10). In this case, the 

antenna was oriented parallel to the butt cleat direction. 

 

Similar to the LLL site, we began the calibration study with a published value for the 

dielectric constant for coal (4.5) (GSSI, 1994). We also examined the perimeter of each 

calibration pillar for obvious signs of geologic anomalies, and none were observed. 

During the tests, the dielectric constant was adjusted in the SIR-2 unit until the arrival 

time of the reflected signal (expressed in terms of depth) approximated the dimension of 

the calibration pillars. The value of the dielectric constant when the antenna was placed 

parallel to the face cleat was determined to be 3.0 and when placed parallel to the butt 

cleat was 4.5. It is believed that this difference is related to the orientation of the coalbed 
joint system, possibly the discontinuous nature of the butt cleat and the impact on the 

variables described above. Table 2 shows the SIR-2 System set-up used for each 

antenna. Similar to the LLL calibration test, deep scan standard set-up parameters were 

used for each antenna. The values shown in the table, with the exception of the vertical 

high and low pass filter settings, are standard default values. Adjustments to the vertical 

low pass filter settings were made to eliminate high frequency noise (snow) from the 

data. Adjustments to vertical high pass filter settings were made to eliminate low 

frequency noise (tilt) from the data (GSSI, 1994). 

Table 2. SIR-2 System set-up used for GPR scans at the SRCM. 

Parameter 

Setting for 

100 MHz

Antenna 

Setting for 

200 MHz

Antenna 

Setting for 

300 MHz

Antenna 

Setting for 

400 MHz

Antenna 

Setting for 

80 MHz

(MLF)

Antenna 

Data collection mode Continuous Continuous Continuous Continuous Continuous 

Range, ns Varied1 Varied1 Varied1 Varied1 Varied2

Samples per scan 512 512 1024 512 512 

Resolution, bits 16 16 16 8 16 

Number of gain points 4 4 4 6 4 

Vertical high pass filter, MHz 25 30 30 30 15

Vertical low pass filter, MHz 200 400 600 800 160

Scans per second 16 32 32 32 32 

Horizontal smoothing, scans 0 5 5 4 0

Transmit rate, KHz 64 64 64 64 64

Dielectric constant 

(parallel to face cleat) 3.0 3.0 3.0 3.0 3.0 

Dielectric constant 

(parallel to butt cleat) 4.5 4.5 4.5 4.5 4.5 

1. Varied from 300 to 1000 ns. 

2. Varied from 300 to 1200 ns. 

 

GPR Capability Testing - LLL 

To test the capability of the GPR system at the LLL site, an area of workings known 

locally as the “ramp” (primary escapeway) was selected that runs subparallel to the trend 

of the D-Drift. The ramp area forms the transition from the old workings to the new 

workings of the mine. The D-Drift is 1,706 ft long, 6.9 ft high and 19.7 ft wide and it 

was thought that because this structure is so large that it would make a good target for 

testing the GPR system capabilities. A total of 11 stations leading away from the 

intersection of the ramp and the D-Drift were selected for antenna locations. At each 

station along the ramp, the antenna was elevated approximately 3 ft above the mine floor 

(because of the dip of the strata) and aimed toward the D-Drift. Straight-line 

measurements were made from the mine map perpendicular to the trend of the D-Drift to 

each antenna location. This measurement proved to be extremely helpful when 

examining the records during post-processing of the GPR data. 

The results of the tests are shown in table 3. An example of an interpreted radar record 

showing the observed anomaly (D-Drift) is displayed in figure 11. Figure 12 shows a 
comparison of radar records for the 80- and 100-MHz antennas. Note that the anomaly, 

believed to be the abandoned mine workings, appears at about the same position in each 

radar record. A value of “Yes” in the table indicates that an anomaly in the record was 

observed at the approximate distance to the 

D-Drift. A value of “No” in the table indicates that no anomalies were observed at the 

approximate distance to the D-Drift. From the results of the tests at the LLL, it appears

that deepest depth of penetration at the test site was about 85 ft. 

Table 3. Results of GPR Tests at the LLL. 

Frequency of Antenna 

Location Distance, ft 100-

MHz

200-

MHz

300-

MHz

400 -

MHz

80- 

MHz

(MLF)

A (Calibration site) 381 Yes Yes Yes Yes Yes

B (Calibration site) 671 Yes Yes Yes Yes Yes

A 92 Yes Yes Yes Yes Yes

B 292 Yes Yes Yes No2 Yes 

C 452 Yes Yes Yes Yes Yes

D 582 Yes Yes Yes Yes Yes

E 662 Yes Yes Yes Yes Yes 

F 712 Yes Yes No No Yes

G 852 Yes No No No Yes

H 1282 No No No No No

I 1592 No No No No No

J 1572 No No No No No

K 1782 No No No No No

1 Distance to other side of pillar. 

2 Distance to D-Drift. 

GPR Capability Testing - SRCM 

At the SRCM, the test of the GPR system took on a different form. Here, a pre-1905 

abandoned mine existed adjacent to the No. 18 Room. Maps obtained from the Office of 

Surface Mining’s Mine Map Repository indicated that the mine had been entered in June 

1922, but it is not clear if mining or only surveying work was conducted in the mine at 

that time (Robertson, 2003). Therefore, only the relative extent of the workings could be 

determined. In addition, an in-seam borehole was drilled in the late 1980’s from the 

SRCM to the northeastern part of the abandoned mine as part of an environmental 

research project by the USBM. Since the drilling records no longer exist, it is unknown if 

the borehole was accurately surveyed. Nevertheless, the information available from the 

mine map, indicated that the abandoned mine workings were penetrated at a depth of 

about 210 ft. 

To test the GPR system, it was decided to select locations near the site of the borehole in 

the SRCM in an effort to detect the nearby abandoned mine workings. A total of five 

stations were selected. During each test, the antenna was elevated approximately 6 in 

above the mine floor and aimed toward the abandoned mine. Straight-line measurements 

of propagation distance were made from the mine map to the abandoned mine at each 
antenna location. This measurement proved again to be extremely helpful when 

examining the records during the post-processing work on the GPR data. The results of 

the tests are summarized in table 4. Examples of interpreted anomalies in the radar 

records are displayed in figures 13-15. Figure 16 shows a comparison of radar records 

for the 80- and 100-MHz antennas. Note that the anomaly, believed to be the abandoned 

mine workings, appears at the same position in each radar record. 

Similar to the test at the LLL site, a value of “Yes” in the table indicates that an anomaly 

in the record was observed at the approximate location of the either the other side of the 

pillar (for calibration points A-C) or the abandoned mine (points D-H). A value of “No” 

in the table indicates that no anomalies were observed in the record at the approximate 

location of either the other side of the pillar (for calibration points A-C) or the abandoned 

mine (points D-H). From the results of the tests at the SRCM, it appears that deepest 

depth of penetration at the test site was about 205 ft. 

 

Table 4. Results of GPR tests at the SRCM 

Frequency of Antenna 

Location Distance, ft 100-

MHz 

200-

MHz 

300-

MHz 

400-

MHz 

80-MHz

(MLF) 

A (Calibration site) 471 Yes Yes No No Yes

B (Calibration site) 421 Yes Yes No No Yes

C (Calibration site) 761 Yes No No No Yes

D 2002 Yes No No No Yes

E 2052 Yes No No No Yes

F 2502 No No No No No

G 1952 Yes No No No Yes

H 2202 No No No No No

1 Distance to other side of the pillar. 

2 Estimated distance to abandoned mine. 

Directional Drilling at the SRCM 

As a method of ground truthing our radar data and to confirm the location of the 

abandoned mine, Target Drilling of Pittsburgh, PA partnered with NIOSH to drill a 

confirmation horizontal borehole from the SRCM to the abandoned mine. Target 

Drilling has significant experience in drilling underground horizontal boreholes for 

coalbed methane recovery, coalbed exploration, abandoned mine verification, and water 

drainage (Kravits, 2002). The drilling equipment and procedures employed in this effort 

were same used for horizontal boreholes, which can extend over 4,000 feet. The drill rig 

was set-up in the No. 18 Room of the SRCM and about 6 ft from the existing borehole. 

The planned trajectory for the borehole was along a line that would penetrate the 

northernmost extent of the abandoned mine workings. This trajectory was selected 

because the mine map information provided by the Office of Surface Mining, the 

available information about the old borehole, and the interpreted GPR records all 

indicated that the abandoned mine was correctly located, but little information existed 

about the northern area of the abandoned mine. 
The electrohydraulic drill rig used for this work consisted of three major components; the 

drill mast and controls; an electric/hydraulic power pack; and a self contained 

electric/hydraulic triplex water pump (figure 17). The high-pressure triplex water pump 

boosts water pressure to drive a downhole motor. The downhole tooling used consisted of a 

PCD (polycrystalline diamond) drill bit, connected to a short nonmagnetic downhole motor, a 

permissible survey system called Downhole Drill Monitor (DDM), and 30 feet of 

nonmagnetic drill collars. The downhole motor has a bent subhousing behind the bit. When 

drilling, the bent housing exerts a force on the sidewall of the hole causing the bit to deflect 

in the opposite direction. Through proper orientation of the bent housing, it is possible to 

steer the trajectory of the borehole. 

The permissible DDM survey tool, housed inside a nonmagnetic pressure barrel and drill 

collar sits directly behind the downhole motor and is only ten feet behind the bit. The short 

distance between the bit and the survey tool improves the accuracy of bit projections, which 

is particularly important when drilling thin coalbeds. Nonmagnetic drill collars and 

downhole motors are utilized to prevent magnetic interference with the survey tool. The 

survey tool uses magnetometers and accelerometers to measure changes in the earth’s

magnetic field, and gravitational vector, respectively. Those changes are converted into 

positional and elevation changes in the borehole. NT-sized (2-3/4 in outside diameter by 10 

ft long) drill rods with the signal wire permanently mounted inside the rod make up the 

balance of the drill string. The drill rods are high-strength core rods that can bend with the 

borehole. The approximate maximum bend per drill rod is 1.5 degrees. 

The signal wire assembly Modular Electrically Connected Cable Assembly (MECCA) inside 

the drill rods transmits the survey data from the DDM’s downhole unit to the uphole monitor 

and computer, where the data are processed into positional readouts. The MECCA couples 

automatically when two drill rods are screwed together, which means there is no lost drilling 

time due to signal wire connections. In this operation, Target Drilling utilized its permissible 

DDM MECCA to accurately establish the borehole position. Positional surveys were 

conducted for every 10 feet of directional drilling and provided the drill operator with real 

time borehole survey data including borehole azimuth, inclination and toolface alignment 

(figure 18). The DDM uphole monitor box then calculates borehole left/right position and 

elevation distance from the start of the borehole. The demonstrated accuracy of the survey is 

within ±1.0o

, and much more accurate results have been documented. Regardless of depth in 

the borehole, it only takes about five seconds to collect, process and display a positional 

survey using the DDM. The ability to survey quickly provides increased survey frequency 

without sacrificing drilling time, increases directional control, and promotes high drilling 

productivity. 

Wellhead control is of paramount importance as it prevents an uncontrolled discharge of 

water or gas when abandoned mine workings are encountered. In this operation a 4-inch 

diameter, 14-ft long collarpipe with valve assembly was grouted into the rib. Once the 

collarpipe grout was set and tested, the horizontal borehole was drilled. The borehole 

penetrated the abandoned mine working at a depth of 238 ft and was completed in about 3 

hours. Figure 19 shows the side view trajectory of the borehole. Note the change in 

horizontal trajectory is caused by changes in the orientation of the bent sub during drilling. 
Figure 20 shows the final position of the borehole relative to the abandoned mine and the 

SRCM. It is unknown why the borehole did not penetrate the workings at a depth of about 

220 ft as measured from the mine map. Perhaps the outline of the mine as shown on the old 

map does not accurately reflect the extent of the mine workings in this area. 

Summary and Conclusions 

In this study, ground penetrating radar was tested to determine its ability to resolve 

adjacent mine workings. The work was conducted at two NIOSH locations – an 

underground coal mine and an underground limestone mine using a variety of antennas 

(100-, 200-, 300-, 400-MHz and an 80- MHz MLF antenna). In the case of the limestone 

mine, the maximum depth of penetration, where the adjacent mine workings could be 

resolved was 85 ft. 

In the case of the coal mine, it was found that the dielectric constant for the coalbed 

varied depending upon whether the antenna was placed parallel to the butt cleat or face 

cleat direction. The value of the dielectric constant when the antenna was placed parallel 

to the face cleat was determined to be 3.0 and when placed parallel to the butt cleat it was 

4.5. This observation is considered significant because depth determination errors could 

be made for anomalies found in the radar records during post-processing work. The 

maximum depth of penetration where the abandoned mine working could be resolved 

was 205 ft. This depth of penetration was achieved using both the 100-MHz and 80-MHz 

MLF antennas. 

It appears that ground penetrating radar can be used to scan rib and face areas to 

determine the near proximity of abandoned mines. Large areas of the unmined coalbed 

can be scanned from the active mine quickly using this technology. From this work, it 

has been determined that significant experience must be obtained with the radar 

technology (including post-processing software) and the material being mined before 

confident interpretations can be made. It is unclear from these tests if similar results can 

be obtained if the abandoned mine workings are flooded. Future testing of this 

technology should address this issue. 

At this time, directional drilling of horizontal boreholes (with downhole surveying) is 

undoubtedly the best technology for accurately determining the location of abandoned 

mines. Proper advance planning for borehole layout and accurately surveying active 

workings can enable a mine operator to avoid problem areas. Given the continuing 

problem of inaccurate abandoned mine maps, it may be possible to utilize ground 

penetrating radar for initial studies followed by directional drilling to accurately delineate 

the extent and position of adjacent abandoned mine workings.

References

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Voids and Mine Safety, Executive Order No. 2002-10, September 4, 2002, 3 p. 
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v.3, p.406-410. 

Geophysical Survey Systems, Inc. (GSSI), 1994, SIR System – 2 Operation Manual, 

Manual # MN72-140, 91 p. 

Knight, R, and A. Endres, 1990, A New Concept in Modeling the Dielectric Response of 

Sandstones: Defining a Wetted Rock and Bulk Water System; Geophysics 55, No. 5, pp. 

586-594. 

Knoll, M.D., 1996, A Pertophysical Basis for Ground-Penetrating Radar and Very Early 

Time Electromagnetics, Electrical Properties of Sand-Clay Mixtures, PhD dissertation, 

University of British Columbia, 316 p. 

Kravits, S.J., 2002, Proven Benefits of Target Drilling Inc.’s In-Mine Directional Drilling 

Technology for Abandoned Mine Verification, Abstract from the Symposium on 

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West Virginia, <http://www.msha.gov/inundation/symposiumabstracts.pdf>, 12 p. 

Martinez, A, and Byrnes, A.P., 2001, Modeling Dielectric-Constant Values of Geologic 

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Figure 1. Layout of the NIOSH Safety Research and Experimental Mines. 

Figure 2. Layout of the NIOSH Lake Lynn Laboratory Experimental Mine. 
Figure 3. Photo of Engineer using the SIR-2 System. 

Figure 4. Photo of Engineer holding 80-MHz (Multiple Low Frequency) antenna. 
Figure 5. Photo of 100-MHz antenna (as configured antenna size 33 in by 44 in). 

Figure 6. Photo of 200- (antenna size 24 in by 24 in), 300- (antenna size 27 in by 31 in) 

and 400-MHz antennas (antenna size 12 in by 12 in).
Figure 7. Layout of test pillar at LLL and examples of the 100-MHz interpreted radar records for the calibration 

dashed arrow shows the direction of the transmitted radar pulse. 
Figure 8. Station A – SRCM layout map and the 100-MHz interpreted radar record for the calibration tests. Not

shows the direction of the transmitted radar pulse. 
Figure 9. Station B – SRCM layout map and the 100-MHz interpreted radar record for the calibration tests. Not

shows the direction of the transmitted radar pulse. 
Figure 10. Station C – SRCM layout map and the 100-MHz interpreted radar record for the calibration tests. No

shows the direction of the transmitted radar pulse. 
Figure 11. Layout of stations for radar capability testing at LLL and an example of the 100-MHz interpreted rad

Note the dashed arrow shows the direction of the transmitted radar pulse.
Figure 12. Interpreted radar records for the 80- and 100-MHz antennas at station D - LLL. 
Figure 13. Layout of stations for radar capability testing at the SRCM and an example of the 100-MHz interpret

(station D). Note the dashed arrow shows the direction of the transmitted radar pulse. 
Figure 14. Layout of stations for radar capability testing at the SRCM and examples of 100-MHz interpreted rad

(stations E & F). Note the dashed arrow shows the direction of the transmitted radar pulse. 
Figure 15. Layout of stations for radar capability testing at the SRCM and examples of 100-MHz interpreted rad

(stations G & H). Note the dashed arrow shows the direction of the transmitted radar pulse. 
Figure 16. Interpreted radar records for the 80- and 100-MHz antennas at station E - SRCM
Figure 17. Photo of electrohydraulic drill rig that was used to drill the horizontal borehole. 

Figure 18. Target Drilling Engineer performing survey of borehole using DDM MECCA unit. 
Figure 19. Side view trajectory of the borehole. 

Figure 20. Final position of the new borehole relative to the abandoned mine and SRCM.