In this study, a parametric study was conducted using FLAC3D numerical models to examine the impact of oblique loading, generated from seam dip, on the strength and the failure propagation pattern of a stone pillar using two simplified geometry types. In type 1, the sidewalls of the pillars were assumed to be perpendicular to the roof and the floor, while in type 2, the sidewalls of pillars were assumed to be vertical. The complex pillar geometry in dipping mines was frequently modeled using these two geometries. To capture a complete picture of the effect of seam dip on pillar stability, the modeled width-to-height (W/H) ratio of the pillars, in situ stress field, and pillars roof/floor interfaces were systematically varied to account for the potential distribution of values for these parameters across the underground stone mines in USA. Results from the numerical modeling indicate that dipping pillars have reduced strength compared with horizontal pillars. Also, an asymmetric failure propagation pattern could be obtained depending on an interaction between the W/H ratio, seam dip, in situ stresses, and pillar geometry.

Ground control is the science of studying and controlling the behavior of rock strata in response to mining operations. Ground-control-related research has seen significant advancements over the last 40 years, and these accomplishments are well documented in the proceedings of the annual International Conference on Ground Control in Mining (ICGCM) [1]. The ICGCM is a forum to promote closer communication among researchers, consultants, regulators, manufacturers, and mine operators to expedite solutions to ground control problems in mining [2], [3], [4], [5], [6], [7]. Fundamental research and advancements in ground control science define the central core of the conference mission. Providing information to mine operators is a priority, as the conference goal is to offer solutions-oriented information. In addition, the conference has included innovative technologies and ideas in mining-related fields such as exploration, geology, and surface and underground mining in all commodities. Many new ground control technologies and design standards adopted by the mining industry were first discussed at ICGCM. This conference is recognized as the leading international forum for introducing new ground-control-related research and products.

The sudden collapse of approximately 3 Ha of room-and-pillar workings at a limestone mine in southwestern Pennsylvania in 2015 resulted in an air blast that injured three mine workers. Subsequent investigations showed that an area encompassing 35 pillars had collapsed. The pillars were 9–10 m wide and up to 18 m high. A notable geologic feature is the through-going joints that dip at 50–80° and can extend from the roof to the floor of the pillars. These structures are thought to have weakened the pillars well below the strength that is predicted by empirical equations for hard-rock pillar design. This paper presents the relevant geotechnical data related to the collapsed area and numerical model results that were used to estimate the pillar loading underneath the variable topography, and compares the pillar loads to some established hard-rock pillar strength equations. The outcome is also compared to a strength equation that was developed specifically for limestone mines in which the negative impact of large angular discontinuities is explicitly accounted for. The results show that established hard-rock pillar strength equations do not adequately account for the impact of large through-going discontinuities on the strength of slender pillars. The equations would have significantly overestimated the strength of the pillars at the case study mine. The critical state of the workings would have been predicted correctly by the limestone pillar strength equation that accounts for the large discontinuities.

An underground limestone mine in eastern Ohio was experiencing significant floor heave and roof falls, attributed to high horizontal stresses. Areas of the mine showing floor heave were monitored with roof-to-floor extensometers and photogrammetry surveys to determine the rate and magnitude of heave. Extensometer data were recorded hourly at four locations across adjacent entries while photogrammetry surveys of the floor were performed at the same locations every two to five weeks. A final survey was performed using an I-Site 8200 laser scanner. Following instrumentation, floor heave up to 10.1 cm (4 in.) was measured by the extensometers, photogrammetric reconstructions and laser scanner over a six-month period. The extensometers were biased by the location where they were placed, failing to consistently capture the location and extent of floor heave and cracking. The photogrammetry surveys were not precise enough to capture small magnitude movements. Mining in the area was halted and within several months the floor movement and incidence of roof falls were significantly lessened.

Ground control is the science of studying and controlling the behavior of rock strata in response to mining operations. Ground control-related research has seen significant advancements over the last 36 years, and these accomplishments are well documented in the proceedings of the annual International Conference on Ground Control in Mining (ICGCM) [1]. The ICGCM is a forum to promote closer communication among researchers, consultants, regulators, manufacturers, and mine operators to expedite solutions to ground control problems in mining [2], [3], [4], [5], [6], [7], [8]. Fundamental research and advancements in ground control science define the central core of the conference mission. Providing information to mine operators is a priority, as the conference goal is to offer solution-oriented information. In addition, the conference has included innovative technologies and ideas in mining-related fields such as exploration, geology, and surface and underground mining. Many new ground control technologies and design standards adopted by the mining industry were first discussed at ICGCM. Therefore, this conference is recognized as the best forum for introducing new ground control-related research and products.

A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues. Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.

In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the Central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.

Design of rib support systems in U.S. coal mines is based primarily on local practices and experience. A better understanding of current rib support practices in U.S. coal mines is crucial for developing a sound engineering rib support design tool. The objective of this paper is to analyze the current practices of rib control in U.S. coal mines. Twenty underground coal mines were studied representing various coal basins, coal seams, geology, loading conditions, and rib control strategies. The key findings are: (1) any rib design guideline or tool should take into account external rib support as well as internal bolting; (2) rib bolts on their own cannot contain rib spall, especially in soft ribs subjected to significant load - external rib control devices such as mesh are required in such cases to contain rib sloughing; (3) the majority of the studied mines follow the overburden depth and entry height thresholds recommended by the Program Information Bulletin 11-29 issued by the Mine Safety and Health Administration; (4) potential rib instability occurred when certain geological features prevailed - these include draw slate and/or bone coal near the rib/roof line, claystone partings, and soft coal bench overlain by rock strata; (5) 47% of the studied rib spall was classified as blocky - this could indicate a high potential of rib hazards; and (6) rib injury rates of the studied mines for the last three years emphasize the need for more rib control management for mines operating at overburden depths between 152.4 m and 304.8 m.

Ground control is the science of studying and controlling the | behavior of rock strata in response to mining operations. Ground | control-related research has seen significant advancements over | the last 37 years, and these accomplishments are well documented | in the proceedings of the annual International Conference on | Ground Control in Mining (ICGCM) [1]. The ICGCM is a forum to | promote closer communication among researchers, consultants, | regulators, manufacturers, and mine operators to expedite solutions to ground control problems in mining [2–6]. Fundamental | research and advancements in ground control science define the | central core of the conference mission. Providing information to | mine operators is a priority, as the conference goal is to offer solutions-oriented information. In addition, the conference has | included innovative technologies and ideas in mining-related fields | such as exploration, geology, and surface and underground mining. | Many new ground control technologies and design standards | adopted by the mining industry were first discussed at ICGCM. | Therefore, this conference is recognized as the best international | forum for introducing new ground control-related research and | products. | Professor Syd Peng (West Virginia University), on his own initiative, organized the First Conference on Ground Control in Mining | in the summer of 1981. Dr. Peng keenly recognized that in order to | advance the state-of-the-art in ground control, a forum was | urgently needed whereby researchers, practitioners, equipment | manufacturers, and government regulators could meet regularly | and exchange information in a timely manner. Beginning in | 2016, the conference was taken over by the Society for Mining, | Metallurgy & Exploration (SME). Four researchers, Brijes Mishra | (West Virginia University), Kyle Perry (Missouri University of | Science and Technology), Heather Lawson (NIOSH), and Michael | Murphy (NIOSH), were chosen to serve as a secondary team from | the conference’s organizing committee to ensure that the ICGCM | continues to advance the science of evasive ground control problems and develop solutions through current mine design strategies, | operational practices, and engineering interventions. Ted Klemetti | (NIOSH) was added to the team in 2017 and will serve as the conference chair for the 38th and 39th conferences.

Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining.

Seismic monitoring provides a useful means for detection and | evaluation of events resulting from mining activity. Seismic | signature characteristics such as arrival times, amplitudes, duration and frequency content can indicate the nature and location of | the source. In the past, most mining-related seismic measurements have focused on events such as rockbursts, production | blasts from quarries, roof falls and rock fractures [1,2,3,4]. However, little or no effort has been expended towards examining the | characteristics of a signature emanating from a methane and coal | dust explosion in an underground mine. The Sago Mine disaster in | 2006 provides an example of why these particular signatures | should be researched. A small amplitude signal was identified on | records of the regional seismic network stations that were closest | to the mine [5]. The epicentral location of the small amplitude | signal was at the Sago Mine. However, it was unclear whether the | signature represented the explosion itself or another type of | mining-related seismicity such as a large roof fall. This paper | presents findings from a study aimed at examining seismicity | from methane and coal dust explosions by analyzing the attenuation and duration of seismic signatures collected from controlled | methane and coal dust explosions, with potential applications to | forensic studies of mine explosions such as the Sago Mine | disaster.

Examination of seismic records during the time interval of the Sago Mine disaster in 2006 revealed a small amplitude signal possibly associated with an event in the mine. Although the epicenter of the signature was located in the vicinity where the explosion occurred, it could not be unequivocally attributed to the explosion. A greater understanding about the seismicity from mine explosions is required in order to properly interpret critical seismic information. A seismic monitoring system located at NIOSH’s Lake Lynn Experimental Mine has monitored 16 experimental methane and coal dust-based explosions. This paper describes the research conducted to quantify a relationship between measured values of radiated seismic energy and peak explosive pressure generated. The radiated seismic energy takes into account seismic signature characteristics such as the frequency content, amplitude, and duration. On the other hand, the size of the explosion is a function of the experimental design, dependent on factors such as the presence of an explosion-containment structure, the mine geometry, and the amount of initial explosive fuel used during the explosion. The seismic signatures from methane and coal dust explosions were analyzed using standard waveform analysis procedures. The procedures used to estimate the radiated seismic energy were conducted using self-produced programs, which are explained in this paper. The radiated seismic energy estimates were considered to be relative values for each experiment. A relationship was derived to correlate the relative radiated seismic energy to the size of the explosion, defined as the peak pressure generated. It was also observed during this study that an explosion-containment structure can act as a major seismic source. Recommendations are made, based upon the findings of this study, for improved collection of seismic data in the future.