Improving the Capability for Real Time Assessment of Roof Conditions 

Through Intelligent Roof Bolt Drilling Operations 

Robert Anderson, Design Engineer 

J. H. Fletcher & Company
 

Huntington, WV 

L. J. Prosser, Research Scientist 

NIOSH-Pittsburgh Research Laboratory 

Pittsburgh, PA
 

ABSTRACT 

Advance knowledge of roof conditions can lead to improvement 

in roof control strategies that will reduce roof falls and ultimately 

will reduce injuries to mine workers. J.H. Fletcher and Company, 

in cooperation with West Virginia University, has been developing 

a system to meet these needs by collecting torque, thrust, and 

rotation speed data during drilling operations. Recent

improvements in analysis algorithms to detect anomalies in the roof 

structure as well as various display enhancements for real time 

mapping and evaluation of roof structures have been incorporated 

into current Fletcher Information Display system. The unit has also 

been housed in an explosion-proof container to allow use in coal 

mine applications. Recently, the system has undergone extensive 

field trials in several limestone mines and one coal mine. During 

these trials, the National Institute for Occupational Safety and 

Health assisted Fletcher in verifying the accuracy of the roof 

mapping capability of the system by comparing the display 

information to bore hole scoping observations and drill corings. It 

was concluded from this assessment that the intelligent drilling 

system can complement scoping and core analysis to provide a 

more complete picture of roof strata and is capable of seeing 

features or conditions that are not always obvious in these more 

traditional methods. 

INTRODUCTION 

 The FLETCHER® information display system had its roots in a 

1992 research and development project to use a Programmable 

Logic Controller (PLC) to monitor drilling operations. Later, a 

Drill Control Unit (DCU) was developed to automate the drilling 

and bolting cycle for improved safety and productivity. The DCU 

is connected to sensors that measure drill bit torque, thrust, rotation 

speed and position as well as vacuum or water pressure. It adjusts 

the drilling parameters to avoid stalling of the drill, breaking the 

bit, or bending the drill steel while maintaining optimum drilling 

speed. As the system evolved, various parameters from the DCU 

were recorded for analysis. It was realized that the data showed 

trends that could be useful to the mine engineer or geologist in 

evaluating the condition of the mine roof. 

A software program was developed to analyze and interpret the 

data, graph the material hardness and display the location of voids 

or other discontinuities in the mine roof structure. The program 

presents a bar graph in shades of gray with lighter shades indicating 

softer material. A depth scale is shown beside the graph. Voids, 

rotation events and water events are marked with colored lines and 

letters. Rotation events are stalls or other sudden changes in 

rotation speed or torque. Water events are sudden changes in water 

pressure which may indicate that the drill steel is being plugged 

with soft material. Figure 1 shows a typical grayscale bar graph 

from the original software. 

Figure 1. Grayscale bar graph from the original system. 
The software was tested in the laboratory and in the mine and 

was refined to improve its accuracy. In a recent project with West 

Virginia University (WVU), the software was modified to 

communicate in real time with the drill control unit and display the 

information as the holes were being drilled. With this new system, 

graphs illustrating information from four separate drill holes were 

displayed side-by-side so that trends could be easily seen. The 

display and analysis can be activated through a rugged touch screen 

panel installed on the bolting machine to facilitate use underground 

by the roof bolter or other mine officials (see figure 2). 

Figure 2. FLETCHER® Information Display 

ADVANTAGES OF REAL-TIME ROOF MAPPING 

WITH THE FLETCHER® INFORMATION DISPLAY 

An Abundance Of Data Is Gathered And Analyzed 

Core drilling, bore-scoping or scratch testing is done 

infrequently. With the Fletcher intelligent drill system and 

Information Display, every hole that is drilled in automatic mode 

has a graph displayed and corresponding data file recorded for 

analysis. Trends are visible as drill hole information from several 

holes are displayed side-by-side in real time during drilling or can 

be recalled from saved files for an historical perspective. 

No Additional Work or Equipment is Required 

Core drilling and bore-scoping require additional equipment and 

personnel to perform these activities. Usually, they are done after 

drilling and bolting operations are complete. If problems are 

realized, then the bolter may have to return to the area to install 

additional bolts or longer bolts. Conversely, real-time roof 

mapping is achieved with the FLETCHER® intelligent drill system 

and Information Display during the normal drilling operation for 

bolting. Hole data is recorded automatically. No input from the 

operator or additional work is necessary and adjustments to the 

bolting strategy can be made in a more timely manner. 

Consistent Results are Possible 

The drill data is interpreted by the computer and displayed in a 

manner that is easily read by the operator. No special training or 

expertise is required. Bore-scoping, scratch testing and core 

drilling require interpretation by skilled personnel. Results may 

vary depending on who is interpreting the data. 

Historical Records are Created 

Data files can be backed up on a flash drive and carried above 

ground for later viewing and analysis by mine engineers or 

geologists. The files are automatically organized in folders by date 

and sequence number to facilitate historical record keeping. 

Optionally, at the start of work in a section, the operator can input a 

prefix which will be added to the beginning of each file name so 

that data files can be sorted by section identification. The grayscale 

hole graphs and line graphs can be printed out for reports and 

documentation as needed. 

Trending Shows What Other Methods May Miss 

No single hole graph may be 100% accurate in predicting voids. 

Other factors in the drilling process may occasionally cause false 

indications in the graph. For example, any sudden change in 

hydraulic pressure, a broken drill bit or binding drill steel could 

show up as a change in the hole graph. Viewing several graphs 

from the same area will show trends, such as a light color for a 

softer band of material. Even though no open void is detected, this 

may indicate a location where a separation may later occur. These 

soft bands may not be visible with a bore-scope or a scratch tool 

especially with an inexperienced user. 

The Computer And Display Have Other Uses 

Parts books, operations manuals and maintenance manuals can 

be stored and displayed on the drilling machine. Image files can be 

viewed on the display. Video from a back-up camera or bore-scope 

can be viewed. Data collected by the computer can be used for 

machine diagnostics and event logging. 

RECENT IMPROVEMENTS TO THE SYSTEM 

Several improvements have been made to the original system, 

including: 

•	 Based on experience in a limestone mine using a 

percussive (hammer) drill, algorithms were revised to 

detect mud seams by water events, where the drill control 

unit reacts to changes in water pressure and alters the 

drilling parameters to prevent the drill steel from 

plugging up. 

•	 The computer’s spinning hard drive was replaced with 

solid state flash memory for better durability. 

•	 An uninterruptible power supply was added for soft 

shutdowns in case of power loss. 

•	 A virtual keyboard was added to the program to allow the 

operator to enter a section number or other prefix to the 

file name. 

•	 A back-up video display was added as a menu item for 

interfacing with a rear-facing video camera to facilitate 

backing up of the roof bolter in poor visibility conditions. 

The video image can be reversed as it would be seen in a 

rear view mirror. 

•	 A print function was added to allow the user to make 

hard copies of the display information. 

•	 An explosion proof housing was designed and built to 

house the Information Display so that it could be tested in 
 

an underground coal mine. In this application, an 

intrinsically safe infrared mouse was used to interact with 

the computer since the touch screen was not accessible. 

•	 The software was revised to work with a new generation 

of Drill Control Unit and to read a different file format 

from the pendant recorder, a handheld data recording 

device which is connected to the DCU. 

TESTING THE SYSTEM IN AN UNDERGROUND 

COAL MINE 

In another joint project with WVU, a test machine was built for 

use in an underground coal mine. An older single-boom roof bolter 

was rebuilt with modern components including the latest generation 

of drill head and drill control unit. The FLETCHER® Information 

Display was installed in an explosion-proof housing on the 

machine. Figures 3 and 4 show the coal test machine and the 

information display. 

Figure 3. Roof bolter used for testing in underground coal mine. 

Figure 4. Information display in explosion proof housing. 

The machine was first tested in the laboratory and then moved to 

a West Virginia coal mine. The first location where the system was 

tested was close to the mine opening and showed very little change 

in the roof structure throughout the drilling depth. Approximately 

60 holes were drilled at different feed pressure and RPM 

combinations. Two core drill samples were taken from this area for 

analysis at WVU. The drill data files and core drill samples were 

unremarkable, showing a continuous homogenous material in the 

mine roof. 

The test machine was moved to another section of the mine 

where there had previously been roof problems including a large 

roof fall. Figure 5 shows this area and gives a cross section of the 

roof strata in this area. 

Figure 5. Section of roof adjacent to large roof fall. 

In this area, thirty more holes were drilled and two more core 

samples were taken. Because of roof height limitations, the core 

drills had to be done some distance away from the group of drilled 

holes. There was some concern that the core drill results might not 

be a good representation of the other drilled holes. Nonetheless, 

the core samples had several discontinuities and the drill data files 

showed events as well. When viewing the hole graphs side-byside, it was obvious that there was some change in roof strata at a 

depth of about 15 in (see figure 6). 

Figure 6. Several hole graphs showing discontinuity trends in the 

mine roof near the 15 in horizon as indicated by the breaks in the 

bar graphs. 

Scoping holes were also analyzed using a small bore scope (less 

than 1 in diameter) as shown in figure 7. Video files were recorded 

for each hole. Initially, the bore-scope videos showed few 

discontinuities in the holes. Only two of the holes had obvious 

voids (see figure 8). The holes were flushed out with water, 

assuming that dust from the drilling might be obscuring the voids. 

The holes were bore-scoped a second time and again there were not 

clear voids at the locations indicated on the drill data files. A 

scratch tool was used to feel for soft bands or ledges in the holes. 
Discontinuities were found in almost every case at or near the 

locations indicated by the drill data files. Fifteen more holes were 

drilled in this area during another visit with similar results. 

Figure 7. FLETCHER® Bore Scope. 

Figure 8. Typical void, approximately 3⁄4” high. 

Even when no open voids were detected, the hole graphs showed 

trends such as the locations of soft bands relative to the bolting 

horizon. Figure 9 shows such a trend in one series of holes 

recorded at the coal mine. 

Figure 9. Location of soft bands within mine roof. 

The core drilled holes were also bore-scoped. Both holes had 

three distinct voids. The first was at about 3 in depth. The second 

void was near the location of soft area detected in the other drilled 

holes. The last void was near the top of the holes at a depth greater 

than had been drilled in the other holes. 

TESTING THE SYSTEM IN AN UNDERGROUND 

LIMESTONE MINE 

A Maryland limestone mine elected to bolt a section of roof 

where there had been problems. This provided another opportunity 

to test the roof mapping system at a different limestone mine. 

NIOSH accompanied J. H. Fletcher in observing these tests and 

reviewing the results. 

In this case, the roof bolter had the Drill Control Unit and a 

pendant recorder but no real-time display installed. A notebook 

computer was used instead to display and record the data. Four 

holes were drilled and bore-scoped at one location. Only one of the 

drill data files showed a possible void but no void was visible when 

bore-scoping the hole. The other holes in this area showed nothing 

remarkable in the data files or bore-scope videos. 

Several holes were drilled and bolts were installed in another 

section of the mine where roof problems had occurred. One of the 

holes, which did not have a bolt installed, was bore-scoped and 

clearly showed a void at a depth of 39 Inches. There was no data 

file recorded for this hole. Another hole was drilled in the same 

area. Both the data file and the bore-scope video for this hole 

clearly showed a void at the same location. Figure 10 shows the 

hole graphs with the void marked. Figure 11 shows the void as 

seen by the bore-scope. 

Figure 10. Hole graphs with void at 39-in depth marked. 

Figure 11. Void as observed from bore-scope video. 
A Missouri limestone mine has a percussive type roof drill and 

bolter with the FLETCHER® Information Display installed.. This 

system has been used successfully there for some time. Tests were 

performed recently with the latest version of the software and the 

new bore-scope for verification. 

Figure 12. Mud seams at first location. 

Three holes were drilled in one section and all three showed 

water events in the drill data files (see figure 12). These are events 

where the Drill Control Unit reacts to seams of mud which tend to 

plug the water flow through the drill. Mud seams were visible with 

the bore-scope at all three holes at locations consistent with the drill 

data. The mine engineer has been using the data from the 

Information Display to track these mud seams to set the roof 

elevation and make sure that bolts are not anchored in soft material. 

Three more holes were drilled and scoped in another section of 

the mine. Only the first of these holes showed a water event in the 

drill data file. The bore-scope video for this hole shows a mud 

seam at that location. The video from the other two holes showed 

similar features that were small enough not to have plugged the 

drill. Figure 13 shows the hole graph along with bore-scope photos 

and a superimposed scale. The larger mud seam was 

approximately 3⁄4 in thick and triggered a water event in the drill 

control unit. 

Figure 13. Mud seams at second location. 

A Pennsylvania limestone mine which has the pendant recorder 

on a roof bolter offered another opportunity to record drill data files 

and compare them to bore-scope video. Again, NIOSH was 

present to observe these tests. Here, four holes were drilled in two 

different sections of the mine. Three of the holes showed large clay 

seams near the top of the hole. These were visible in the drill data 

files as lighter shades of gray. When the software sensitivity was 

adjusted they were marked as voids. The clay seams were clearly 

visible in the bore-scope videos. Figures 14 and 15 show the hole 

graphs and a bore-scope image. 

Figure 14. Hole graphs showing clay seams. 

Figure 15. Bore-scope image of clay seam. 
A photo from outside the mine opening shows the red clay 

above the limestone seam (see figure 16). 

Figure 16. Red clay above limestone. 

CONCLUSIONS 

1. No one method shows everything. 

Bore-scope video showed hairline and vertical cracks that did 

not show up with the intelligent drill system and Information 

Display. Rock layers which varied in color but had similar 

hardness were obvious in the bore-scope but not visible in the 

drill data files or with the scratch tool. Scratch testing found soft 

areas shown on the Information Display and some edges that 

were not obvious when using the bore-scope. The 

FLETCHER® Information Display will complement these other 

methods to provide a more complete picture of roof strata that is 

not dependent on personal interpretation. 

2. The system needs to be adjusted for individual machines and 

mine conditions. 

Many factors affect the thrust, torque and other parameters used 

to calculate material hardness and locate voids. These include 

drill size, bit type, bit sharpness, type of rock in the roof, style of 

drill (percussive vs. rotary) type of feed mechanism (rotary 

hydraulic motor vs. cylinder feed), settings for collaring and 

maximum feed pressures, RPM of the drill, and type of cutting 

removal (vacuum or water). An adjustment is provided in the 

software for rotation event and void detection sensitivity. As the 

knowledge base grows with different installations, a group of 

standard settings can be preprogrammed for each machine type 

and mine conditions. 

3. Looking at trends gives a more accurate picture than 

individual data samples. 

With all of these methods of determining roof strata, a single 

sample may not be an accurate representation of the area as a 

whole. Roof conditions may change drastically in a short 

distance. Voids that were clearly visible in one hole were not 

found in holes a few inches away. Core drilled holes which 

were closer to an intersection in the mine showed greater 

separation in voids than holes drilled just a few feet away. The 

FLETCHER® Information Display provides a way to view 

trends that may not be obvious using other methods alone. 

These trends are visible during the normal drilling cycle. 

4. The FLETCHER® Information display is an ongoing 

research and development project that is still evolving. 

More testing and improvements are scheduled.