Bajpayee, T.

Schilling, S.

Stability Mapping to Examine Ground Failure Risk: A Field Study at a 

Limestone Mine
 

T. S. Bajpayee, Lead Research Engineer
 

NIOSH Pittsburgh Research Laboratory
 

Pittsburgh, PA
 

S.R. Schilling, UG Mine Engineer, Geologist
 

Pleasant Gap Mine
 

Graymont, PA
 

ABSTRACT 

As the surface reserves are being depleted, more and more 

stone operators are seeking underground mining options. Stability 

of underground openings is a major concern for the safety and 

productivity. This paper relates to a field study conducted at a large 

underground limestone mine in Central Pennsylvania. Identification 

of hazards leading to ground failures and assessment of roof fall 

risks are important in mitigating injuries. Field observations at this 

mine were integrated with Roof Fall Risk Index (RFRI) mapping 

software recently developed by West Virginia University. The 

system is designed to combine field study data related to geologic 

factors, mining-induced damages, roof profile, and ground water 

influx to generate RFRI maps. The mine has adopted a proactive 

ground control program consisting of comprehensive examination 

of drilling and bolting logs; precision surveying of roof and 

rib; accurate mapping of cutters, falls, and geologic structures; 

and installation of extensometers and microseismic monitoring 

systems. Investment of time and resources has eliminated fatalities 

and lost‐time injuries due to ground fall. This paper presents the 

geologic settings, mining conditions, ground control issues along 

with risk management and control techniques adopted at the study 

mine. 

INTRODUCTION 

One of the major hazards of mining is premature ground failure 

resulting in injuries and fatalities. Falls of roof and rib accounted 

for over nine thousand injuries in the underground mining sector 

from 1996 to 2008. Figure 1 shows the incidence rate (number of 

injuries per 200,000 employee‐hours) of roof fall injuries in stone 

mines during this period (MSHA, 2009). As the surface reserves 

are being depleted, more and more stone operators are seeking 

underground options. Entry stability is a major concern for the 

safety and productivity of underground operations. Entry heights 

in many stone mines range from 6.1 to 18.3 m (20 to 60 ft) and 

such entry heights make it difficult to quickly recognize unstable 

roof conditions. Identification of hazards leading to ground failures 

and assessment of roof fall risks are important in mitigating injuries 

and fatalities in the underground stone sector. Many of the roof 

instabilities are caused by sudden change in geologic structures, 

the presence of fault zones or major discontinuities, and mining 

induced damages. Other causative factors include high horizontal 

stress, influx of ground water, inadequate ground control, improper 

support design, and incorrect support installation. Failure to 

recognize geotechnical risks and implement remedial actions could 

expose miners to rockfall hazards. Reducing the number of ground 

failure injuries and fatalities is one of the goals of the National 

Institute for Occupational Safety and Health (NIOSH). 

 . Incidence Rate per 200,000 Employee‐hours 

1996 0.58 

0.50 

1998 0.52 

0.92 

2000 0.45 

0.52 

2002 0.59 

0.43 

2004 0.31 

0.33 

2006 0.19 

0.29 

2008 0.39 

0.0 0.3 0.5 0.8 1.0 

Figure 1. Incidence rate of roof fall injuries in stone mines, 1996 

– 2008 (after Pappas, 2009). 

The average incidence rate (figure 1) of roof fall injuries is 0.46 

injuries per 200,000 work‐hours with a standard deviation of 0.13. 

The incidence rate has shown an upward trend in 2007 and 2008 

compared to that of 2006. There is a need for further improvement 

by using the techniques of risk management and control. The 

general downward trends in Australian underground mining fatality 

rates are, in part, attributed to the introduction and acceptance of 

risk‐based management systems (Iannacchione et al., 2009). Major 

Hazard Risk Assessment (MHRA) in the geotechnical area has 

been used as a tool to improve miner safety (Potvin and Nedin, 

2003). The Mine Safety Technology and Training Commission 

recommended application of risk‐based systems and techniques to 

enhance worker safety and reduce injuries and fatalities (Grayson 

et al., 2006). This paper presents a description of geologic settings, 

mining conditions, rockmass characterization with geotechnical 

risk assessment, analysis, mapping, and control techniques used at 

an underground stone mine in Central Pennsylvania. 
 

 

GEOLOGIC SETTING AND MINING CONDITIONS 

The mine is extracting limestone using the room‐and‐pillar 

method from the Valentine member of the Linden Hall formation 

belonging to the Lower Middle Ordovician Limestones (Rones, 

1969). The Valentine member is about 21.3 m (70 ft) thick in 

this area and comprises rocks of two closely related lithologic 

types. The upper 15.2 m (50 ft) comprises unlaminated, light‐

gray calcilutites ranging from 0.9 to 1.5 m (3 to 5 ft) in thickness 

(Rones, 1969). The lower 6.1 m (20 ft) is well laminated with 

thickness ranging from 0.3 to 0.9 m (1 to 3 ft) with thin clay or 

fine bentonite partings. The Valentine Limestone comprising lightgray, chemically pure limestone lies above the dark‐gray 12.8‐m 

(42‐ft)‐thick Valley View member of the Linden Hall formation. 

About 9.1 m (30 ft) of the dark‐gray and thinly‐bedded section 

of Centre Hall member of the Nealmont formation lies above the 

Valentine Limestone. The Valentine Limestone generally dips at 

15 degrees and the strike direction runs approximately at N60°E 

(Rones, 1969). 

The southward advance of mining is projected to extend to a 

depth of about 549 m (1,800 ft). The uniaxial compressive strength 

of Valentine Limestone ranges from 100 to 145 MPa (14,500 to 

21,000 psi) and the maximum horizontal stress in the area ranges 

from 14.9 to 29.6 MPa (2,170 to 4,300 psi) in the N80°E direction 

(Esterhuizen and Iannacchione, 2004). A stress control mine design 

plan has been implemented to alleviate the effects of high horizontal 

stress and improve ground stability. Pillars are rectangular having 

their long axis oriented parallel to the maximum horizontal stress 

direction. Pillar size is approximately 46 x 20 m (150 x 65 ft). 

Crosscuts are staggered to develop three‐way intersections. During 

development, rooms are driven to 15.2 m (50 ft) wide by 7 m (23 ft) 

high. Subsequently, an additional 11.3 m (37 ft) of rock is extracted 

by floor benching. Presently, the overburden thickness ranges from 

outcrop to approximately 304.8 m (1,000 ft). Roof sag monitors 

and multi‐point extensometers are routinely used to monitor roof 

movement. Additionally, a surface‐based microseismic system has 

been installed to monitor microseismic emissions associated with 

strata fracturing. 

The dark‐gray, thin‐bedded Centre Hall Limestone immediately 

above the Valentine is often laminated, and considered undesirable 

to constitute the immediate roof beam. On the other hand, the 

top 1.8 m (6 ft) of Valentine Limestone is massive and competent 

to constitute a stable roof beam. In areas where the mining 

depth exceeds 274.3 m (900 ft), a layer of Valentine Limestone 

of thickness 1.8 m (6 ft) is left at the top of the entry to act as 

an immediate roof beam. In addition, a stable roof profile is 

maintained, where possible, by implementing precision blasting. 

A significant outcome is enhanced ground stability, reduction of 

guttering, and diminution of roof fractures and roof failures. 

GEOTECHNICAL ISSUES 

Geotechnical issues related to underground stone mines require 

careful consideration for ensuring safety of the workforce and 

stability of the openings. Roof falls ranging from minor local 

skin failures to entire pillar failures have been experienced by 

the underground stone mining community. A limited few of 

these ground failures resulted in injury. Ground control may be 

described as the ability to predict and influence the behavior of 

rock in a mining environment to ensure safety of the workforce and 

serviceability of the mine openings (MOSHAB, 1997). Ground 

control in limestone mines can be complex because the entries are 

fairly wide and have large heights. Rocks falling from a high roof 

have significant injury potential. During a survey of roof stability 

issues in underground stone mines in the Eastern and Midwestern 

U.S., Esterhuizen et al. (2007) observed that roof instabilities were 

primarily related to excessive horizontal stress or unfavorable 

geologic structures that caused block fallout or beam failure 

of the bedded roof rocks. Roof falls larger than 0.91 m (3 ft) in 

length, typically consisting of multiple fragments, were primarily 

associated with the followings: 

•		Block failure – large discontinuities and joints associated with 

fall, 

•		Beam failure – bedded layers in the roof failed under gravity 

loading, 

•		Stress related failure – shearing and buckling due to horizontal 

stress, 

•		Caving failure – progressive spalling of blocky roof or weak 

strata. 

Esterhuizen et al. (2008) reported a pillar design methodology 

based on a study of pillar performance issues in stone mines. 

Three essential components of an effective ground control program 

are: (1) systematic coordination of geologic structures and stress 

parameters, (2) state‐of‐the‐art entry and pillar design consideration, 

and (3) sound plan of ground support and reinforcement action 

(MOSHAB, 1997). Loading a pillar beyond its peak resistance 

often results in load shedding, yielding, shearing, or collapse. 

Rockmass Characterization for Excavation Stability 

Structural geology greatly influences entry stability in 

underground mines. Moebs (1977) and Hylbert (1978) investigated 

the role of structural features on the stability of coal mine roof 

rocks. Rockmass classification and support design progressed a 

long way from the traditional tunnel support design of Terzaghi 

(1946). The Rock Quality Designation (RQD) has been used to 

provide a quantitative assessment of rockmass quality (Deere 

and Deere, 1988). This was followed by Rock Structure Rating 

by Wickham et al. (1972). Bieniawski (1989) published a 

Geomechanics Classification system, also known as the Rock 

Mass Rating (RMR) system. Articles related to extensions of 

the Bieniawski classification system for new applications were 

published by Laubscher (1990) and Kendorski et al., (1983). The 

Coal Mine Roof Rating System (CMRR) by Molinda and Mark 

(1994) has been extensively used for roof rock characterization. 

The Norwegian Geotechnical Institute (Barton et al., 1974) 

proposed a Tunneling Quality Index (Q) based on a large number 

of field data. A significant rationale of rock characterization relates 

to examining stability and determining support requirements to 

increase the life and serviceability of underground openings. Many 

of the earlier attempts to characterize ground stability and prevent 

premature roof failures were based on rockmass characterization, 

entry size, support design, and ground water influx. In stone mines, 

the thickness of the immediate roof beam and the entry width 

greatly influence roof stability. 

GEOTECHNICAL RISK MANAGEMENT 

Risk management and control techniques have long been used in 

many industries including nuclear, petro‐chemical, environmental, 

manufacturing, and aerospace. There is a rich collection of 
literature including national standards (MIL‐STD‐882D, 2000; 

CAN/CSA Q850‐97, 1997: AS/NZS 4360, 2004) and industry 

publications (Potvin and Nedin, 2003; MOSHAB, 1997; MOSHAB, 

1999; and DME, 2003). A structured risk management process 

typically accepts risk levels to as‐low‐as reasonably achievable 

(ALARA) or as‐low‐as reasonably practicable (ALARP) as an 

integral part of day‐to‐day operation. The concept of roof fall 

risk management is important for the underground mining sector. 

Iannacchione et al. (2009) examined risk management techniques 

to mitigate injuries and fatalities for mining applications. Several 

codes of practice to mitigate roof fall risk in the mining industry are 

available. 

The Mine Safety Technology and Training Commission 

recommended application of risk‐based systems and techniques 

to enhance safety and reduce injuries and fatalities (Grayson 

et al., 2006). Considerable national expertise is available for 

the application of risk management techniques in the mining 

sector (Iannacchione et al., 2009). The Mine safety and Health 

administration (MSHA) has articulated an informal risk analysis 

concept consisting of Stop, Look, Analyze, and Manage (SLAM). 

SLAM requires mine operators, supervisors, miners, and 

contractors to take proper precautions before performing any task. 

The goal is to prevent accidents by conducting an informal risk 

assessment before starting new tasks and by controlling the hazards 

related to each task. Hazard is defined as a source of potential 

harm or a situation with a potential to cause loss. Risk is defined 

as the chance of something happening that will have an adverse 

impact upon objectives; it is measured in terms of consequences 

and likelihood (Potvin and Nedin, 2003 and NSWDPI, 1997). 

Generally, risk is calculated by multiplying the probability of 

occurrence of an event likely to cause injury by its consequences 

(Iannacchione et al., 2009). Roof falls from a 7‐m‐ (23‐ft) high 

entry usually have serious consequences (Iannacchione et al., 

2007b). 

Evolution of Geotechnical Risk Management for Mining 

Applications 

The Australian mining industry became interested in the 

application of structured risk‐based management and control 

techniques to alleviate the risk of rockfall injury and progressed 

considerably in the transition from prescriptive health and safety 

standards to proactive, duty‐of‐care concept (DOCEP, 2006). The 

regulatory agencies provided guidelines and formulated procedures 

to help the industry (AS/NZS 4360, 2004; NSWDPI, 1997; QDME, 

1999; and QMC, 1999). Australian regulations require mines 

to use risk management techniques on a regular basis to mitigate 

injuries and fatalities. The Mineral Industry Safety and Health 

Center (MISHC) at the University of Queensland (Joy, 1999 and 

2006) developed a model and framework for Mineral Industry Risk 

Management (MIRM). The Mineral Industry Risk Management 

Gateway (MIRMGATE) at http://www.mirmgate.com/is maintained 

by MISHC. A host of tools were made available for assessment, 

analysis, control, and mitigation of risk (NSWDPI, 1997; Potvin 

and Nedin, 2003; and Joy, 2006). 

The South African mining community also accepted risk‐based 

procedures for mitigating rockfall injuries (Swart and Joughin, 

1998; Van Wijk et al., 2002; and Lind, 2005). Mining sectors in 

Canada, United Kingdom, and USA became interested in using 

risk‐based procedures in mitigating rockfall hazards and injuries. 

Figure 2 shows the basic structure of rockfall risk management 

process (MOSHAB, 1999). The process, listed below, begins with 

a sound planning followed by a detailed hazard identification, risk 

analysis and assessment, and finally risk management and control. 

Planning 

Hazard Identification 

Communicate and Consult

Risk Analysis and 

Assessment 

Monitor and Review 

Risk Management and 

Control 

Figure 2. Risk management process to mitigate roof fall injury 

(after MOSHAB, 1999). 

•		Planning – identify team members, collect geotechnical 

information, and establish acceptable risk levels in consultation 

with subject matter experts, relevant employee groups, and 

management. 

•		Hazard Identification – classify geotechnical parameters and 

conditions that could cause or have a potential to cause roof 

fall injury. Potvin and Nedin, (2003) identified a host of 

parameters that could influence rockfall probability including 

rockmass quality, structural geology (joints, faults, angular 

discontinuities, etc.), mining‐induced stress, blast damage, size 

and shape of excavation, and influx of ground water. 

•		Risk Analysis and Assessment – determine the likelihood of 

roof fall injury due to each defect condition, determine the 

degree or severity of injury, and rank all risks with appropriate 

weighting factors. 

•		Risk Management and Control – implement strategies to 

reduce risk to an acceptable level, eliminate exposure to high 

risk activities, install instrumentation for monitoring risk, and 

implement audit and review process. 

Table 1 is a simplified version of generic risk matrix for 

geotechnical hazard analysis. The roof fall probabilities are low, 

medium, and high and the severity of consequences are also low, 

medium, and high. This is a 3 x 3 matrix resulting in nine possible 

risk rankings. 

RISK ASSESSMENT, MANAGEMENT, AND CONTROL AT 

THE STUDY MINE 

Hazards leading to potential roof failures and possible injuries 

were carefully examined during this field study. Accessible 

underground areas including production faces were visited during 

the data collection phase. Field measurements were limited to the 

areas where miners usually work or travel. 
Table 1. Generic risk matrix for geotechnical hazard analysis. 

Severity of Consequences Probability of occurrence of mishap (roof fall) 

Low (Possible) Medium (Likely) High (Very likely) 

High (Critical) M S H 

Medium (Marginal) L M S 

Low (Negligible) L L M 

L: Low mishap category ‐ operation with (SLAM). 

M: Medium mishap category ‐ time limited operation with approval from safety director. 

S: Serious mishap category ‐ essential to suppress risk to an acceptable lower level, use monitoring and control. 

H: High mishap category ‐ must treat and mitigate risk to an acceptable lower level 

Roof Fall Risk Index (RFRI) 

Iannacchione et al. (2007a) developed a procedure for 

determining RFRI based on the observed values of defect categories 

(figure 3) and their respective weights. The major groupings for 

computing RFRI were (a) geologic factors, (b) mining‐induced 

failures, (c) roof profile, and (d) ground water influx. The geologic 

factors were (a) angular discontinuity, (b) joint frequency, and (c) 

strata strength. The mining‐induced failure parameters were (a) 

shear rupture surface, (b) joint separation, (c) lateral strata shift, 

and (d) strata separation. The roof profile parameters were (a) 

rock debris on the floor and (b) roof shape. Parameters for water 

influx were damp roof, drippers, and steady flow. The study area 

was divided into small measurement areas where risk ranking 

parameters were considered uniform. The size of measurement 

areas ranged from 15.2 x 15.2 m (50 x 50 ft) at the intersections to 

15.2 x 68.6 m (50 x 225 ft) in the entries. 

Angular

Discontinuity

(G1)

Angular

Discontinuity

(G1) Joint

Frequency

(G2)

Joint

Frequency

(G2)

Strata

Strength

(G3)

Strata

Strength

(G3)

Shear

Rupture

Surface

(M1)

Shear

Rupture

Surface

(M1)

Joint

Separation

(M2) 

Joint

Separation

(M2) Lateral

Strata

Shift

(M3)

Lateral

Strata

Shift

(M3)

Strata

Separation

(M4)

Strata

Separation

(M4)

Rock

Debris

on Floor

(R1)

Rock

Debris

on Floor

(R1)

Roof

Shape

(R2)

Roof

Shape

(R2)

Ground

Water

(W1)

Ground

Water

(W1)

Angular

Discontinuity

(G1)

Angular

Discontinuity

(G1) Joint

Frequency

(G

(M2) 

Ground ( ( GG

1) 

y 

)2G(

cneuqerF

ointJ

)3G(

ngthtreS

atartS

Ground 

2)

Joint

Frequency

(G2)

Strata

Strength

(G3)

Strata

Strength

(G3)

Shear

Rupture

Surface

(M1)

Shear

Rupture

Surface

(M1)

Joint

Separation

Joint

Separation

(M2) Lateral

Strata

Shift

(M3)

Lateral

Strata

Shift

(M3)

Strata

Separation

(M4)

Strata

Separation

(M4)

Rock

Debris

on Floor

(R1)

Rock

Debris

on Floor

(R1)

Roof

Shape

(R2)

Roof

Shape

(R2)

Water

(W1)

Ground

Water

(W1)

Angular 

Discontinuity 

1) 

Angular 

Discontinuity Joint 

Frequency 

(G2) 

Strata 

Strength 

(G3) 

Shear 

Rupture 

Surface 

(M1) 

Shear 

Rupture 

Surface 

(M1) 

Joint 

Separation 

(M2) 

Joint 

Separation 

(M2) Lateral 

Strata 

Shift 

(M3) 

Lateral 

Strata 

Shift 

(M3) 

Strata 

Separation 

(M4) 

Strata 

Separation 

(M4) 

Rock 

Debris 

on Floor 

(R1) 

Rock 

Debris 

on Floor 

(R1) 

Roof 

Shape 

(R2) 

Roof 

Shape 

(R2) 

Water 

(W1) 

Ground 

Water 

(W1) 

Water influx 

Geologic 

factors 

Roof profile 

Mining induced failures 

Figure 3. Parameters for evaluating roof fall risk at the study 

mine (after Iannacchione et al., 2007a). 

The roof fall probability of a measurement area was assigned 

low (1), medium (2), or high (3) based on its RFRI value. RFRI 

values below 30 were assigned low (1) probability and higher 

than 40 were assigned high (3) probability. RFRI values ranging 

between ≥ 30 and ≤ 40 were assigned medium (2) probability 

(Iannacchione et al., 2007b). Areas representing medium (2), 

or high (3) probability were routinely bermed off to prevent 

unauthorized entry. Only roof remediation activity under the 

supervision and guidance of geotechnical experts were allowed in 

such areas. 

Roof Fall Hazard Exposure 

A qualitative risk rank of a measurement area could be estimated 

by combining its RFRI value with the miner exposure. Miner 

exposure may be represented by the duration of time miners are 

expected to occupy different work locations. Miner exposure could 

be grouped as Continuous, Intermittent, Rare, or Non‐existent. A 

continuous exposure rating is appropriate for production face areas 

and main haulage routes where miners are present during most of 

their working shift. An intermittent exposure rating is appropriate 

for areas occasionally visited by miners during the work shift. The 

secondary haulage routes and non‐production development faces 

could represent such areas. Parts of the mine rarely visited by 

miners could be assigned rare exposure rating. Bermed‐off areas, 

considered off‐limits to the miners, represent non‐existent exposure 

rating. 

RFRI Mapping Software 

The RFRI mapping software developed by Prof. Heasley 

(Heasley and Wang, 2005), conveniently plots color‐coded risk 

levels on a mine map. RFRI mapping, an application program, 

was created as a run time extension for the PC‐based AutoCAD1 

1 Mention of any company or product does not constitute endorsement by the National 

Institute for Occupational Safety and Health. 

drafting program. This application program has been integrated 

with the LaModel boundary element software package (Hardy and 

Heasley, 2006). The process of creating a RFRI map involves the 

following steps: 

•		Open the AutoCAD file containing the mine map and load 

the stability application program. Laptop computers may be 

conveniently used if analysis is desired while collecting data 

in underground locations. 

•		Create a new layer and draw the boundary of each 

measurement area. After several steps of running the 

program, a data entry screen similar to that shown in figure 4 

will be available to help identifying parameters in each defect 

category. 

•		A drop down menu will appear for each defect category. Select 

the desired parameter in each defect category (figure 4). The 

system will assign the required category values to compute the 

RFRI. Table 2 is an example of defect categories and typical 

assessment values for few measurement areas. 
• Based on the assessment values, the program computes the 

RFRI. It also assigns a color code for each measurement area 

in the AutoCAD map (figure 5). 

Table 2. Typical assessment values used in figure 4 for computing RFRI. 

CATEGORY 

A25 A27 

Angular discontinuity (G1) 1 1 

Joint frequency (G2) 3 2 

Strata strength (G3) 3 2 

Shear rupture surface (M1) 1 1 

Joint separation (M2) 1 4 

Lateral strata shift (M3) 1 1 

Strata separation (M4) 1 1 

Rock debris on floor (R1) 4 2 

Roof shape (R2) 3 1 

Ground water 1 2 

RFRI 26 27 

RFRI MEASUREMENT AREA NO. 

A29 A43 C19 C25 C29 C37 C42 

1 1 1 1 1 1 1 

2 3 3 2 3 2 2 

2 2 3 2 2 2 2 

2 1 4 3 1 2 1 

5 4 4 1 1 1 1 

1 1 1 1 1 1 1 

1 1 1 1 1 1 1 

2 2 6 4 2 4 4 

2 2 3 2 1 2 2 

4 1 1 1 1 1 1 

34 28 41 27 20 24 22

Figure 4. Data input format in AutoCAD. 

RFRI Values 

<30 Low 

30 to 40 M30 to 40 Medium 

>40 High

N 

Figure 5. RFRI plot of a study area (after Iannacchione et al., 

2007a). 

Roof Fall Risk Management and Control 

The mine has implemented a procedure for routinely inspecting 

underground work stations and berming off areas of potential roof 

fall risk. A RFRI rating of 30 or more signifies potential roof fall 

risk. The purpose of berming off is to prevent unauthorized entry 

during the roof remediation process. Roof remediation is carried 

out under the supervision of experienced personnel. Subsequently, 

such areas are inspected to ensure compliance with safety and 

legal requirements. Investment of time and resources to enhance 

safety had a positive impact and the mine has not experienced any 

lost‐time injuries or fatalities due to ground failure since 2001. 

Miners, contractors, and supervisors are allowed to work 

and travel in areas having low (<30) RFRI rating. However, 

all employees and contractors are required to observe MSHA’s 

concept of Stop, Look, Analyze, and Manage (SLAM) (http:// 

www.msha.gov). The goal is careful observation of work areas and 

implementation of safety measures before starting any new task. 

Underground mining is associated with certain inherent 

geotechnical hazards that cannot be totally eliminated, and must 

be controlled and managed during the life of mining (Hebblewhite, 

2003). Roof fall is considered an inherent geotechnical hazard 

(table 3). The study mine adopted a proactive approach to identify 

and mitigate roof fall risks. A microseismic monitoring system and 

a host of roof deformation sensors were installed for early detection 

of symptoms leading to roof failure. Also, potential unstable areas 

were bermed off to prevent entry and eliminate miner exposure. 

This practice proved helpful in mitigating rockfall injuries. 

Appendix A provides brief information about management, control, 

and audit of geotechnical risks at this mine. 
Table 3. Inherent geotechnical hazards associated with room-and-pillar mining. 

Hazard Consequences 

Room or intersection failure Operator safety, equipment damage, loss of access, and production disruption. 

Local pillar collapse Production disruption, employee safety, loss of access. 

Regional pillar failure (pillar run) Loss of reserves, production disruption, potential worker safety issues, and 

Regional closure (creep) possible subsidence consequences.

SUMMARY AND CONCLUSIONS 

Underground mining is associated with inherent roof fall 

hazards that cannot be totally eliminated and must be controlled 

and managed during the life of mining. This paper relates to 

application of an integrated RFRI mapping technique that provides 

a convenient way of plotting comprehensive color‐coded RFRI 

maps. RFRI maps help to identify areas of potential roof instability. 

The major groupings for computing RFRI are geologic factors, 

mining induced failures, roof profile, and ground water influx. 

The geologic factors are angular discontinuity, joint frequency, 

and strata strength. The mining induced failure parameters are 

shear rupture surface, joint separation, lateral strata shift, and strata 

separation. The roof profile parameters are rock debris on the floor 

and roof shape. Parameters for ground water influx are damp roof, 

drippers, and steady flow. 

Stability of underground openings is a major issue for the safety 

and productivity at the study mine. The mine had implemented a 

proactive roof fall risk management, control, and audit plan outlined 

in Appendix A. The plan proved helpful in eliminating lost‐time 

injuries and fatalities related to ground failure. In summary, the 

results of this study are encouraging for further exploration toward 

implementing a comprehensive ground control plan in underground 

stone mining. 

DISCLAIMER 

The findings and conclusions in this report have not been 

formally disseminated by the National Institute for Occupational 

Safety and Health and should not be construed to represent agency 

determination or policy. 

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APPENDIX A 

Risk Management, Control, and Audit 

Work areas: Inspect face, roof, and rib areas in each heading 

where miners are working or scheduled to work. Communicate 

observations to miners and foreman. Pay particular attention to 

any changes in lithology, bedding planes, joint systems, faults, 
 

 

 

 

 

 

and secondary minerals. Communicate all information to the next 

shift and engineering. Follow the written procedures for all roof 

inspection, monitoring, support, and repair works. 

Drilling, blasting, and mechanical scaling: Record all observations 

in the drilling, blasting, and scaling logs. Pay particular attention 

to geology. Surface sounding and scaling report must be 

communicated to the next shift and engineering. 

Haulage, escapeways, portals, and work stations: Inspect regularly 

haulage, escapeways, portals, and all underground work stations. 

Record observations and communicate information to the next shift 

and engineering. 

Roof wedges, spalls, and dribbles: Paint roof wedges, spalls, and 

dribbles. Install additional lighting (stationary or portable) in the 

area. Communicate information to the next shift and engineering. 

Roof bolting: Observe for drill speed, dust, and water consumption. 

Use scratch tool to detect fractures in roof holes, and record crack 

location (depth) and extent of strata separation. Communicate 

information to the next shift and engineering. 

Extensometers: Install extensometers or roof sag monitors to 

measure roof deflection. Record observations related to roof 

deformations. Communicate information to the next shift and 

engineering. 

Roof falls, gutters, and changes in strike or dip: Roof falls, 

roof gutters, and any changes in the strike or dip (direction or 

magnitude) must be located and shown on the mine map. Their 

effect on ground stability should be evaluated. 

Microseismic monitoring: The mine has installed a monitoring 

system to detect microseismic emissions associated with rock 

fracturing. Unusually high level of microseismic activity is 

routinely investigated. 

Mining plan modifications: The mine emphasizes the concept of 

mitigating roof fall risk by design changes and has modified mining 

plan to alleviate the effects of horizontal stress at a deeper section 

of the mine.