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By Larry DeGraff

With the increase of new mine development in the past several years, many coal mines have decided to self- perform the design and construction for their slope development projects. The development process of determining the proper configuration is challenging, and a major economical consideration. Greenbrier Smokeless Minerals engineering staff and consultants, along with DSI/American Commercial, developed a support configuration that was best suited for their slope. The developmental process took into consideration the length of slope, depth of slope at the high-wall transition, economics of a single or multiple entries, waterproofing, stresses on the steel supports and lagging during the backfilling operation. This paper describes the developmental concept of using a single entry, side by side configuration, using steel ?Banjo String? supports with steel plank lagging, to develop a long term permanent installation in a cut and cover application.

Jan 1, 2009

By Axel Preusse

On the basis of the Law on Financing Hard Coal Mining dated 28 December 2007, the subsidized German hard coal mining industry will be shut down to the end of the year 2018 in a socially acceptable manner; in 2012 this decision will be reassessed. Even after the abandonment of all mining activities subsequent burdens are inevitable. In this paper, the possible long-term effects resulting from a mining industry history, which is spanning more than 200 years, and their possible consequences are pointed out, in particular in connection with the abandonment of mine water drainage measures which is economically meaningful in the long term. According to the decision situation as it presents itself today, this point in time will be far beyond 2018. In preparation for this, an action framework is to be developed in areas possibly affected.

Jan 1, 2008

By William G. Pariseau, Michael K. McCarter

"The challenge of estimating mine-wide subsidence and linkages to seismicity over tabular deposits is addressed by a special finite element technique (dual node - dual mesh). Subsidence and mine-induced seismicity begins near the face when caving occurs and propagates to the surface as extraction reaches a critical extent. Thus, the challenge is to obtain details at the face at the meter scale and also at the surface over the whole mine at the kilometer scale. Interactions between old and new sections of a mine are automatically taken into account with this technique. The finite element method is well established technology based on fundamentals of physical laws, kinematics and material laws. With this technique, no empirical ""scaling"" or fitting computer output by input data ""adjustment"" to mine measurements is necessary. Capability is demonstrated for doing practical whole-mine subsidence analysis from first principles. Mine-induced seismicity is shown to correlate well with face advance and element failure.INTRODUCTIONSeismicity associated with coal mining has been under study for several years by a team at the University of Utah. Team members include mining faculty, research geophysicists and students from the Departments of Mining Engineering and Geology & Geophysics. Mines in central Utah that have been studied include the Trail Mountain Mine (Pariseau, 2015; Pariseau and McCarter, 2015), the Beehive Mine, also known as the Des-BeeDove (Pariseau, 2014), and the Crandall Canyon Mine (Pariseau, 2015). These mines were developed from outcrops in the Wasatch Plateau coal field west of Price, Utah, where the topography is characterized by . steeply incised canyon drainages and high plateaus with relief of a thousand meters or so.Seismicity associated with coal mining in central Utah has been of interest for many years and includes studies in the Book Cliffs to the east of Price, Utah, where mining is still active (Smith et al, 1974; Agapito, Goodrich and Moon, 1997; Arabasz et al, 2001; Arabasz et al, 2002; Fletcher and McGarr, 2005; McGarr and Fletcher 2005; Maleki, 2005) and to the northwest (Ellenberger et al, 2001). Results of many micro-seismic studies are summarized perhaps best by lannacchione, et al (2005) in stating, ""Deviations from normal strata response can provide useful stability information.""This study concerns a fourth underground coal mine in the southern portion of the Wasatch Plateau coalfield, hereafter referred to as the MINE. Focus is on mining from 2004-2008 with the objective of examining mining in relation to seismicity."

Jan 1, 2016

By P. M. Lin

A subsidence monitoring program over a longwall panel was established (1) to explore the impacts of dynamic subsidence on the ground surface and structures and (2) to correlate the movements between the structures and their corresponding points on the ground. The program consisted of a transverse line survey and a series of survey points around the structures on the ground surface and their corresponding survey points on the exterior walls of the structures. The vertical displacement of each point can be expressed as: where Si is subsidence at i point; Sif is the final subsidence at i point; F is face location in terms of distance from the i point and SD is seam depth. The development of subsidence can be divided into five stages. Damage to the structures starts at the beginning of the second stage, The maximum damage developed in the middle of the third stage. The relationship of the vertical displacement between ground surface and structures can be expressed as: G = aH + b where G is ground displacement, H is structures displacement, and a and b are constants. The relationship is linear. However, the strain is non-linear and more complicated because of the interaction of the ground surface and structure.

Jan 1, 1989

By Jun Lu

There are many factors affecting the strength of pillar, including width-to-height (W/H) ratio, mechanical properties of coal and surrounding rocks, property of partings in the coal, and the interface property between coal seam and the roof/floor. In this paper, the effect of varying pillar?s width-to-height ratio (W/H=3, 5, 7, and 10) and coal/rock interface cohesion (Cj =50 psi, 150 psi, and 300 psi) on pillar strength has been studied. The confinement effect of W/H ratio and interface shear strength is investigated by studying their effects on the average minimum principal stress developed in the pillar. The deformation behavior of the coal pillar is investigated. It is found that the pillar?s transition from strain softening to strain hardening behavior depends on its W/H ratio and the interface shear strength.

Jan 1, 2008

By Peter Zhang

Shield recovery in a longwall move is normally conducted from tailgate to headgate. However, if the face is wide and the immediate roof is weak, difficult conditions with considerable roof sag, excessive shield load, and local roof falls could occur as the shield recovery proceeds to the middle of the face, causing delays in shield recovery. The situation could be aggravated when a pre-driven longwall recovery room is employed. Alternatively, a bi-directional approach for shield recovery, i.e. shield recovery starting from the middle of the face towards both tailgate and headgate, can alleviate the roof sag significantly by quickly withdrawing the shields towards the lower abutment pressure zones at the headgate and tailgate sides. In this case, the bi-directional shield recovery approach was used in a longwall move for a 1450 ft wide face under weak roof conditions. Shields were successfully withdrawn within five days without experiencing significant roof sag. The time-dependent roof-to-floor convergence, shield pressure, and roof conditions were monitored during shield recovery. 3-D finite element modeling was conducted prior to longwall move to evaluate the difference between a uni-directional and a bi-directional shield recovery during a longwall face move. Vertical stress, yield zone in and around the recovery room, load on the shields, and convergence at the center of the shield canopy were obtained from computer modeling, and compared with the data from field monitoring. Finally, the advantages of the bi-directional shield recovery are discussed.

Jan 1, 2007

By Long Fan, Shimin Liu, Guijie Sang

"Weak shale roof falls have long been the main cause for fatalities in underground coal mines. Moisture-induced swelling is one of the root causes for the degradation of roof shales. In this study, slake durability tests are conducted on shale samples collected from Illinois basin coal mines, and different levels of durability are analyzed according to Gamble slake durability classification. There are two main mechanisms influencing the shape of retained fragments after two cycles of wetting and drying: mechanical abrasion and swelling pressure. A prototype optically based shale swelling apparatus is designed and manufactured for the shale free-swelling measurement. The experimental results suggest that swelling pressure tends to deteriorate shale laminations. Moisture-induced swelling of the No. 6 roof shale from Bear Run Mine was measured under 100% relative humidity condition. The measured swelling strain normal to beddings is ~5 to 7 times greater than the swelling strain parallel to beddings. This suggests that interlayer expansion plays a key role in moisture-induced swelling. Cracks induced by swelling pressure tend to occur along the bedding plane and lead to shale deterioration. INTRODUCTION Background Ground falls have long been the cause for nearly 50% of all fatalities in underground coal mines and continue to be one of the greatest safety hazards in underground spaces. Among the various ground fall hazards, roof failure takes up 23% of total fatalities in underground coal mines, of which 13% are due to skin failure and 10% are due to massive roof falls (Mark, Pappas, and Barczak, 2011). Roof failures associated with weak shales are summarized in previous studies (Molinda and Mark, 2010; Aughenbaugh and Bruzewski, 1973; Bajpayee, Pappas, and Ellenberger, 2014; Murphy, 2016). For mine roof instability and failure, two aspects can explain the failure mechanism of weak roofs. One is the elevated stress concentration in lateral direction due to the mining-induced excavation and its stress redistribution around the mine opening (Song and Stankus, 1997; Fan and Liu, 2017; Hill, 1986). The other mechanism is the passive stress-relief due to the strength weakening induced by the ambient moisture and temperature fluctuations during a period of time. Shale is moisture sensitive and presents a lower durability if it is exposed to a highly humid environment for a long time, thus leading to roof deterioration and instability in underground coal mines (Aughenbaugh and Bruzewski, 1976; Stateham and Radcliffe, 1978; Chugh and Missavage, 1981; Klemetti, Oyler, and Molinda, 2009). It is well known that shale is a clay-bearing sedimentary rock and that clay minerals are water sensitive. The moisture uptake for shale will induce the micro-deformation of a shale matrix, thus the structure and strength of shale is a function of time and intensity of moisture exposure. All mine engineers notice moisture-induced shale deterioration; however, the underlying mechanism(s) are still not fully understood due to the complexity of geophysical-chemical water-shale interactions (Huang, Aughenbaugh, and Rockaway, 1986; Hensen and Smit, 2002; Diaz-Perez, Cortés-Monroy, and Roegiers, 2007). The coal mining industry is still in the process of finding a technically sound, cost-effective technology to prevent this unexpected and unpredictable shale roof failure. Therefore, understanding how the moisture-sensitive shale responses to various ambient moisture and what role exposure duration plays in shale roof failure is key to prevent unexpected roof incidents, which will lay the foundation for the long-term roof support design and ground control management."

Jan 1, 2017

By Ted Klemetti, Gabriel Esterhuizen, John L. Ellenberger

"Advanced numerical models can be used to evaluate entry support systems in coal mines. However, these methods require specialized software and specialized skills to create the models and evaluate the results. Practicing support design engineers require a method to rapidly assess a proposed support system for a given geotechnical scenario. A prediction equation that can be used to assess roof support systems has been developed from the results of hundreds of FLAC3D analyses that were conducted during recent research. These models were validated against field cases and empirical design approaches and were found to adequately predict entry stability in coal mines. The understanding developed from the model outcomes was used to develop an equation to predict entry roof stability against large roof falls. Least-squares error analysis was conducted to find appropriate parameters for the nonlinear equation. The developed equation can be solved using spreadsheet software, allowing for rapid assessment of alternative support system performance in variable geological conditions. The performance of the prediction equation is evaluated against empirical design methods and against selected case histories of support practices at currently operating mines. Examples are presented that demonstrate the performance of the equation in variable geological settings. The stability factor (SF) prediction equation can be used as an assessment tool to assist in the design of coal mine roof support systems.IntroductionGround falls represent a significant proportion of injuries and fatalities in underground coal mines in the US. During 2013, ground falls were responsible for 4 of the 14 fatalities and 16.6 % of the 1,577 reportable lost-time injuries (MSHA, 2015). In addition, each year about 400 to 500 large roof falls are reported that can extend up to or above the bolted horizon. Large roof falls and associated ground fall hazards can be mitigated through improved support design.The research presented here particularly addresses the problem of large roof falls that extend more than 90 cm (3 ft) above the roof line of an entry and may extend above the bolted horizon. Smaller roof falls that fall out between supports or extend less than 90 cm (3 ft) above the roof line are excluded. These smaller roof falls can be controlled by appropriate surface support such as roof screen or other skin control methods. Also excluded are roof falls that are associated with an individual geological structure such as a slip of fault. Structure-related instabilities can be controlled by strategically locating individual roof bolts or other supports appropriate for the local situation."

Jan 1, 2015

By Haile Manteqi

In longwall coal mines, estimation of roof strata condition, sequence of loading, and supporting requirements are of a high degree of importance, and they are directly related to production and safety. Also, a prediction of the initial caving distance is rather complicated to calculate, because there are many parameters that effect caving process?roof and floor strata conditions, thickness of immediate roof, depth of cover, excavation geometry, and magnitude, and direction of principal stresses. This paper presents the results of 3D numerical modeling of the initial caving mechanism using the finite difference code FLAC3D at the E1 longwall panel of the Parvade 1 underground mine located in the Tabas area in the central part of Iran. The initial caving distance obtained was 10.4 m. Also, the results of numerical modeling have been compared to the analytical methods, such as Peng?s method. The results show good agreement with each other.

Jan 1, 2012

By Marcel0 Mondring

Transportation and the logistic requirements are set very high for the German coal mining industry. Short transportation resources, crowded quarters, and long transportation distances to destinations are some basic conditions that logistic employees of the mines have to deal with. Therefore, in the context of these processes, human effort and technology are faced with great challenges. There can be a total of 300 transport units, depending on the size of the mine. Every day, they are moved through a nearby 150-km-long transportation network of floor and monorail tracks. Of these transport units, 150 are new, and the other 150 units are split into cross traffic units that are moved only in the underground and return travel units. Beside track-bounded transports, all material transports take place in the shaft. As a result, many involuntary transports and changes in the means of transportation make the daily work more difficult. Typical transports in the shaft include the supply of new materials from above to below, as well as returnable goods from below to above. Cross traffics throughout several levels, which are rather rare, would have to be handled above the shaft. Due to limited shaft capacity, these cross traffics should be avoided when possible. Based on the gas resources in coalmine slopes, track-bounded transports using monorails (powered by diesel or rechargeable means) are preferred. This depends on the road degree, the depth, and track cross section of the shaft/slope. The variety of the material spectrum includes more than 100,000 different types of material.

Jan 1, 2014

By Vincent A. Scovazzo

Many accepted and useful methods have been developed and used for pillar design. Each method has its own particular strengths and weaknesses. Three methods addressed in this paper are; empirical, analytical, and numerical. Each of these methods have their place in pillar design. Analytical methods result in close approximation of the ideal pillar (most economical, stable, or yielding) and are suitable for use in final mine design and in analyzing existing problems. BOYD uses the analytical method to develop site specific mine pillars design equations. An analytical method, one of many developed by BOYD, is presented here and is based on the procedure used by Wilson (1) and others in development of their empirical equations.

Jan 1, 1995

By Arka Jyoti Das, Prabhat Kumar Mandal

"Coal mining in India has a strategic importance for the energy security of the country. Presently, the majority of coal production is coming from open-cast mining. Due to the fast depletion of reserves amenable to open-cast mining, future coal production will depend primarily on underground production. In conventional bard-and-pillar/room and pillar mining as it is practiced in India, the percentage of extraction is very low. In fact, within most Indian coalfields, a large number of coal seams extract only 15- 20% of coal, but no pillar extraction is done due to the presence of surface or sub-surface structures leading to huge amount of coal being locked-up in underground. Spontaneous heating and fire, the accumulation of poisonous gases, severe stability issues, unsafe workings and environmental hazards are all major problems associated with these developed coal pillars, so there is a pressing need for technology in the mining industry to extract this huge amount of coal locked up under different constraints. In this study, we propose that the locked-up coal be extracted by replacing the developed coal pillars with artificial pillars. The paper briefly discusses the extraction methodology designed for this and its evaluation through numerical modeling for applied suitability underground.INTRODUCTIONDriven by rising populations and urbanization, an expanding economy and also a quest for improved quality of life, energy usage in India is expected to increase manifold in the coming years. As for India's energy scenario and its projected future plans, there is no doubt that coal will remain a prime source of energy, even over the next few decades.The majority of coal production in India comes from open-cast mining because of large-scale mechanization, but the coal reserves amenable to open-cast mining are gradually depleting - which may impose adverse impacts on the energy sector if underground production does not increase. Underground coal extraction, meanwhile, is going to become more complicated in near future due to the fast exhaustion of easily mineable coal reserves."

Jan 1, 2016

By Michael Alber

Coal mining by the longwall method typically causes seismic events. This paper describes the research on mining induced seismicity around two specific longwalls at 1100m depth under several old longwalls. A local network featuring 21 geophones has been installed, underground core drilling and an extensive rock testing program were executed. A rock mechanical model featuring a multi-layer strata was created for use with numerical analyses. Seismic events were localized and three different event types are described. Focal analyses yielded distinct modes of failure. Those types are explained by different failure mechanisms, namely fault activation, remnant pillar punching and beam failure. The use of rock mass classification, rock mass strength criteria and in situ stresses together with 2D and 3D numerical analyses allows evaluating the findings from seismology approaches. Conclusions are drawn that the orientation of longwall with respect to the major horizontal stress orientation plays an important role in mine induced seismicity.

Jan 1, 2008

By Morgan M. Sears, lhsan B. Tulu, Ted M. Klemetti

"Why do some room and pillar retreat panels encounter abnormal conditions? What factors deserve the most consideration during the planning and execution phases of mining and what can be done to mitigate those abnormal conditions when they are encountered? To help answer these questions, and to determine some of the relevant factors influencing the conditions of room and pillar (R&P) retreat mining entries, four consecutive R&P retreat panels were evaluated. This evaluation was intended to reinforce the influence of topographic changes, depth of cover, multiple-seam interactions, geological conditions, and mining geometry.This paper details observations made in four consecutive R&P retreat panels and the data collected from an instrumentation site during retreat mining. The primary focus was on the differences observed among the four panels and within the panels themselves. The instrumentation study was initially planned to evaluate the interactions between primary and secondary support, but produced rather interesting results relating to the loading encountered under the current mining conditions. In addition to the observation and instrumentation, numerical modeling was performed to evaluate the stress conditions. Both the LaModel 3.0 and Rocscience Phase2 programs were used to evaluate these four panels. The results of both models indicated a drastic reduction in the vertical stresses experienced in these panels due to the full extraction mining in overlying seams when compared to the full overburden load. Both models showed a higher level of stress associated with the outside entries of the panels. These results agree quite well with the observations and instrumentation studies performed at the mine.These efforts provided two overarching conclusions concerning R&P retreat mine planning and execution. The first was that there are four areas that should not be overlooked during R&P retreat mining: topographic relief, multiple-seam stress relief, stress concentrations near the gob edge, and geologic changes in the immediate roof. The second is that in order to successfully retreat an R&P panel, a three-phased approach to the design and analysis of the panel should be conducted: the planning phase, evaluation phase, and monitoring phase."

Jan 1, 2016

By Robert Anderson

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.

Jan 1, 2007

By John R. Koehler

Available barrier pillar design methods do not adequately account for overburden caving characteristics, the timing and magnitude of associated load transfers, the occurrence of unusual geologic features, or the effects of multiple-panel/multiple-seam mining. To address this problem, the Bureau of Mines, in cooperation with Cyprus Plateau Mining Corporation, conducted a barrier pillar study in a multiple-seam mine setting. Insufficient barrier width resulted in excessive load transfer to an adjacent/underlying section. Consequent entry and pillar deterioration resulted in the section being prematurely abandoned. This paper proposes an approach based on in situ measurements, which includes mine-specific loading conditions in the barrier design process.

Jan 1, 1989

By W. C. Lacy

Stratabound copper ore bodies in thick Proterozoic metamorphosed sedimentary and volcanic rocks at the Tong Kuang Yu Mine in southern Shanxi Province of China were considered as possibly being amenable to block cave mining. Initial evaluation of caving characteristics was based upon old calyx drilling records, limited underground mining experience and geological mapping, a few diamond drill holes and measurements in surface subsidence features. Classification and mapping distribution of rock quality types aided in mine design, prediction of fragment sizing and explosive requirements, cave assist and ground support requirements. Comparison is made between early feasibility predictions and actual mine experience.

Jan 1, 1989

By S. Yamashita

Recently in Japan, unexpected degradation (surface subsidence) at old underground quarry sites, such as 'Ohya-Ishi' (pumice tuff) pit field has often been occurred. At these quarry sites, the excavation was started 20 or 30 years ago with mechanical chain cutter and the Room and Pillar method, and stopped 7 or more years ago. Therefore, a reliable method has been required for an estimation of long term mechanical properties of the rock and for an observation of a stability of rock-pillars or structures. In this study, creep tests under uniaxial compressive load were carried out on the 'Ohya-Ishi', with the aim of estimating the long term stability of the rock. From these results, a creep mechanism of the rock was discussed using the failure mechanism hypothesis proposed by Bieniawski and by others. On this basis, critical time to failure was predicted by the relationship between the logarithm of life time and stress ratio of the sustained axial creep load. Additionally, outline of the monitoring system of AE/MS activity in the field, which have set by the Ohya Aria Consolidate Public Corporation and the others to predict or to prevent the degradation of those residual pillars, is to be reported. Key words : Ohya-ishi, Pumice tuff, Mine pillar, Long term stability, Creep, Critical time

Jan 1, 1996

By Wenbing Guo, Yi Tan, Erhu Bai

"It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequence and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved.The surface movement and deformation caused by coal mining not only influence the ecology environment in the mining area, but damage the surface structures such as buildings, railroads, highways, water bodies and damsr1-31_ The movement of strata and surface caused by mining had disturbed various aspects of industrial and agriculture productions in the mining arear41. The earth dam is a very important water retaining structures, so it must makes sure the safety of dam if mining under it. Therefore, to study the effect of mining on dam and control measures to ensure safety of mining under the dam are important factors for improving the mining recovery ratio, reliving the mining continuity, preventing or reducing damage to the dam.By means of the harmonic mining technologyrs1, theoretical analysis and field observation, the mining method under an earth dam and the mining influences were studied and analyzed in this paper. The mining of a thick coal seam under the dam was carried out safely and successfully."

Jan 1, 2016

By S. J. Jung

A fundamental study of fragment size distribution and characteristics of fracture pattern is presented for the dynamic penetration of a conical bit into coal block. In this paper, damaged zones during crater formation and fragment size distribution were studied. Bit with a sharper tip angle and a smooth body configuration performed better penetration. Results suggest that in coal cutting the trend should be toward the face cleat direction using a sharper angled tip bits which consumes less energy for an optimum range of penetration depths, thus attaining maximum cutting efficiency and reducing fine fragments.

Jan 1, 1989