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By James D. Pile

Following a methane ignition in the active panel of a longwall coal mine, the affected panel was successfully isolated from the rest of the mine. This allowed for the remainder of the mine to return to regular operation, and the conventional practice of having to seal the portals for a defined period of time was avoided. After the affected panel had remained isolated for a regulatorily mandated period of time, it was reopened in preparation for longwall face recovery. As it was not possible to move the shields from their existing positions to facilitate the installation of recovery mesh prior to shield recovery, alternative methods had to be considered to stabilise the gob and minimise flushing, thereby improving operator safety. The objective of the paper is to show how stabilisation of the gob was achieved during shield recovery, thereby minimising flushing, and improving operator safety. Phenolic foam was chosen and injected from between the shields into the gob behind them. This is a technique that has been used to great effect in Germany, to a lesser extent in Australia, but not knowingly to date in the United States. To ensure nothing was left to chance and thereby guarantee the project?s success, the procedure used in Germany was employed, down to the application of equivalent hardware, which was sourced through the North American supplier.

Jan 1, 2013

By George J. Karabin

The Roof Control Division of the Pittsburgh Safety and Health Technology Center, MS HA, is routinely involved in the evaluation of ground conditions in underground coal mines. Assessing the stability of mined areas and the compatibility of mining plans with existing conditions are essential elements in assuring a safe working environment at a given site. Since 1985, the Roof Control Division has successfully used the Boundary Element Method of Numerical Modeling as a tool to aid in the resolution of complex ground control problems. This paper will present an overview of the modeling methodology established and details of techniques currently used to generate coal seam, rock mass, and gob backfill input data. A summary of coal and rock properties used in numerous successful evaluations throughout the country will be included and a set of Deterioration Indices that can aid in the quantification of in-mine ground conditions and verification of model accuracy will be introduced. Finally, a case study will be detailed that typifies the complexity of mining situations analyzed and illustrates various techniques that can be used to evaluate prospective design alternatives.

Jan 1, 1994

By Jiachen Wang

China is the largest coal producing country in the world. Coal is widely distributed in China and thus the mining conditions are complex and diverse. This paper summarizes the important achievements in the last 20 years in various mining methods including the extra thick seam with large mining height top coal caving, the thick seam with large mining height and top coal caving mining, the steep seam with top coal caving and fully-mechanized mining, the thin seam automated mining, and the backfill mining. At the same time, the rapid advance in the development of mining machinery and manufacturing has also contributed to the advancement of coal mining technology and the great improvement of coal mine safety. The future direction of China?s coal mining is to further improve mine safety as to improve the coal recovery rate, promote the pillar less mining technology, develop high-efficiency backfilling technology, develop steep seam high-efficiency mining technology for seams less than 10m thick, and high recovery mining techniques for extra thick seams, improve the reliability of mining equipment, and strengthen the protection and restoration of surface environments and water resources.

Jan 1, 2014

By Keith Heasley

As part of the initial investigation and validation of a new boundary-clement formulation for stress modeling in coal mines. the underground stresses and displacements at two multiple-seam coal mines with unique stress problems are modeled and predicted. The new program, LAMODEL, calculates stresses and displacements at the seam level and at requested locations in the overburden or at the surface. Both linear elastic and non-linear seam materials can he used: and surface effects, multiple seams, and multiple mining steps can be simulated. In order to most efficiently use LAMODEL for accurate stress prediction, the program is first calibrated to the site-specific geo-mechanics based on previously observed stress conditions at the mine. For this calibration process. a previously mined area is "stress mapped" by quantifying the observed pillar and strata behavior using a numerical rating system. Then, the site-specific mechanical properties in the model are adjusted to provide the best correlation between the predicted stresses and the observed underground stress rating. Once calibrated, the model is then used to predict future stress problems abead of mining. At the two case study mines, the calibrated models showed good correlation with the observed stresses, and also accurately predicted upcoming high stress areas for preventive action by the mines.

Jan 1, 1998

By Gabriel Esterhuizen

The roof rock in underground limestone mines in Northern Appalachia can be subject to high horizontal stresses in spite of the shallow depth of the workings. The high stresses can cause roof stability problems. The National Institute for Occupational Safety and Health staff have observed a distinctive asymmetrical mode of failure at the pillar-roof contact in two underground stone mines, which is different from the typical failure mode observed in response to excessive levels of horizontal stress. A dip of greater than 5° was identified as a possible cause of this mode of failure. Numerical model experiments showed that an increase in the dip of the workings can cause an increase in the stress at the up-dip comer of the roof beam. A case study is presented in which failure at the pillar-roof contact was observed where the dip of the workings was 7° in a high horizontal stress field. Numerical modeling showed that the relatively small dip of the workings could have induced stresses changes in the immediate roof that would explain the failures. The model results also showed that this mode of failure is less likely to occur if the limestone pillars contain weak bedding planes that provide stress relief. In addition, the results showed that for the conditions at the case study site, the stress in the roof beam was not sensitive to the thickness of the roof beam or to the excavation span. The high horizontal stresses at this site are an important contributing factor to the observed failures.

Jan 1, 2004

By Anton Sroka

The German hard coal production predominantly derives from underground multiseam mining activities. Beside common surface damages, ?inner mine damages? on underground infrastructures (i.e. main roads, cross cuts and shafts) due to mining excavations occur to an increasing extent. As these "inner mine damages" dramatically increased because of the development towards high performance longwall mining technologies, this matter raised to be a severe problem concerning mining economics. To protect durable and long lasting underground infrastructures, precautionary measures such as suitable mine layouts, adapted planning of mining operations and moderate face advances have to be considered. Some examples of "inner mine damages" recorded by means of mine surveying methods are given in this paper. An empirical-mathematical model based on the principles of mining subsidence engineering methods will be introduced. This model allows to minimize ?inner mine damages? and helps to support and optimize mining processes.

Jan 1, 1999

By Stephen R. Iverson, Jeffrey C. Johnson, Donovan J. Benton, Michael J. Raffaldi, Lewis A. Martin

"The NIOSH ground control safety research program at Spokane, Washington, is exploring applications of photogrammetry to rock mass and support monitoring. This paper describes two ways photogrammetric techniques are being used. First, photogrammetric data of laboratory testing is being used to correlate energy input and support deformation. This information can be used to infer remaining support toughness after ground deformation events. This technique is also demonstrated in a field application. Second, field photogrammetric data is compared to crackmeter data from a deep underground mine. Accuracies were found to average 8 mm, but have produced results within 0.2 mm of true displacement, as measured by crackmeters. Application of these techniques consists of monitoring overall fault activity by monitoring multiple points around the crackmeter. A case study is provided in which a crackmeter is clearly shown to have provided insufficient information regarding overall fault ground deformation. Photogrammetry is proving to be a useful ground monitoring tool due to its unobtrusiveness and ease of use.INTRODUCTIONNIOSH Mine Safety ResearchPhotogrammetry systems have been implemented by the National Institute for Occupational Safety and Health (NIOSH) as part of its ground control research to improve mine safety. Conventional monitoring of ground movement has typically focused on movement of a few discrete points that are marked or anchored to instruments. Loss of a designated point or anchor, or the ability to identify a stable point in an unstable area, have often frustrated monitoring efforts. NIOSH researchers are using photogrammetry to conduct full-field measurements of rock surfaces underground. Periodic measurements of the entire surface of a ramp allow patterns of displacement to be observed. Full-field measurements provide much more insight into ground behavior than point measurements.BackgroundPrevious work by Benton, et al. (2014) discussed laboratory calibration and verification testing of two photogrammetry systems being used by NIOSH researchers. Both systems utilize stereoscopic image pairing techniques for photogrammetric reconstruction. This paper discusses how a laboratory system was used to conduct volumetric analyses of testing of shotcrete panels with varying types of reinforcement. The laboratory system was found to be accurate to within 2 mm. Additionally, a field photogrammetry system was found to produce linear measurements within 1 mm of known lengths in laboratory conditions. This system is currently being used at a deep underground mine to observe ground support conditions and deformations that have occurred. This paper discusses comparison of preliminary volumetric measurements of rib deformation to laboratory tests, as well as comparison of the field system against a crackmeter installed across a fault surface where it intersects the ramp."

Jan 1, 2015

By Chengguo Zhang, Bruce Hebblewhite, Faham Tahmasebinia, lsmet Canbulat

"Coal burst is a dynamic release of energy within the rock (or coal) mass leading to high velocity expulsion of the broken/ failed material into mine openings. This phenomenon has been recognised as one of the most catastrophic failures associated with the coal mining industry, which can often lead to injuries and fatalities of miners as well as significant production losses. This paper aims to examine the mechanisms contributing to coal burst occurrence, with an emphasis on the energy release concept. In this study, a numerical modelling study has been conducted to evaluate the roles and contributions of difference energy components. The energy analysis presented in this paper can help to improve the understanding of energy release mechanisms especially under Australian conditions.INTRODUCTIONCoal burst is one of the most hazardous problems encountered in underground coal mines, which occurs at different locations in a variety of mining systems and operations. This phenomenon always involves a violent and dynamic energy release with large rock mass/coal deformation and ejection that can cause severe damage to openings, equipments and may result in fatalities and injuries.The first coal burst occurrence was reported in Britain in 1738 (Dou 2001). Since then, international experiences are available in Canada, South Africa, USA, former Soviet Union, China, India, France, Germany, Poland and Czechoslovakia. Rice (1935) classified coal bursts as two general types, namely excessive pressure bumps and shock bumps and he further mentioned that pressure bumps are caused when pillar stress exceeds bearing strength. Shock bumps are induced by the breaking of thick, massive strata at a considerable distance above the coal-bed, causing the immediate roof to transmit a shock wave to the coal."

Jan 1, 2016

By Joseph C. Zelanko

Cable bolt support techniques. including hardware and anchorage systems, continue to evolve to meet U.S. mining requirements. For cable support systems to be successfully implemented into new ground control areas, the mechanics of this support and the potential range of performance need to be better understood. To contribute to this understanding, a series of 36 pull tests were performed on 10 ft long cable bolts using various combinations of hole diameters, resin formulations, anchor types, and with and without resin dams. These tests provided insight as to the influence of these four parameters on cable system performance. Performance was assessed in terms of support capacity (maximum load attained in a pull test), system stiffness (assessed from two intervals of load-deformation), and from the general load-deformation response. Three characteristic load-deformation responses were observed. An Analysis of Variance identified a number of main effects and interactions of significance to support capacity and stiffness. The factorial experiment performed in this study provides insight to the effects of several design parameters associated with resin-anchored cable bolts.

Jan 1, 1995

By Richard G. Burdick

The Bureau of Mines', Denver Research Center has been conducting research for the past few years on the use of resistivity methods to locate abandoned mine workings. As this work has progressed, it is apparent that in some cases, in addition to detecting the old workings; stoping, precursive to surface subsidence has also been detected. This paper describes the Automated Resistivity method and discusses sites in Colorado. Wyoming. and Illinois where the subsidence phenomenon has been observed.

Jan 1, 1982

By A. Grenoble

The mining of seams in close proximity can greatly accentuate interaction problems. At distances of less than 110 feet vertically interaction can occur for both over and under mining. Research into ground control problems resulting from undermining a previously mined seam has been carried out using finite element and body-loaded photoelastic modeling methods in conjunction with numerous case studies. Analysis of field data was used to validate and expand the model results. Research findings demonstrate situations under which the worst ground control conditions can be expected to occur for a specified geologic environment, depth, innerburden spacing and mining geometry. Special emphasis has been placed on the effects of pillar load transfer on the lower seam in terms of pillar and floor stability and roof control. Roof and floor condition indexes are used to summarize structural and lithologic conditions in the affected seam. The effects of joint orientation and continuity are incorporated in the analysis and the research results have been compiled into a software package for application by the field engineer.

Jan 1, 1984

By Sandin E. Phillipson

"On April 5, 2010 a massive dust-fueled explosion at a longwall mine in southern West Virginia claimed the lives of 29 miners. The mine had experienced large gas inrushes from the floor on two known previous occasions, and natural gas was found emanating from floor fractures behind the longwall shields after the explosion, indicating a likely fuel source for the initial ignition. In succeeding months, another longwall mine operating in the same seam 15 miles away encountered smaller inflows of natural gas that halted production from two different longwall faces. Production was halted at a third longwall mine, 30 miles south of the first, in May 2011, when explosive levels of methane were detected inby the longwall face on the headgate. The same mine was evacuated on March 20, 2014 when a series of floor gas feeders were encountered on the longwall face. A literature review indicated that there has been little documentation or description of these events, and that their size and frequency are unknown. The most significant floor gas inrushes in the United States are believed to have been associated with longwall mining in the Pocahontas No. 3 Seam of western Virginia, in which an estimated 5.8 x 107 ft3 of natural gas was expended from a floor feeder on the longwall face over a two-week period (Aul, pers. comm.).A variety of mechanisms and circumstances are associated with methane emanations from underground mines. Hyman (1987) defined an outburst as a violent, simultaneous release of gas and comminuted rock material into a working face or the interior of a borehole, and indicated that certain soft or fractured coals have a propensity for outburst based on gas desorption rates. In this mechanism, reservoirs of autogenic gas hosted in pockets of soft, crushed coal surrounded by harder coal are released suddenly as confining stress is removed by mining. Hyman (1987) also suggested that highly stressed, relatively gassy coal that is penetrated by mining-induced fractures could be outburst-prone. Clayton et al. (1993) and Ulery (2008) recognized the importance of faults as potential conduits for gas from adjacent strata into coal mines, and suggested that biogenic gas trapped in adjacent strata could migrate into mined coal seams due to a pressure differential. Ulery (2008) distinguished between an outburst and a blower, the latter defined as an event expending a large amount of gas over an extended time period, most often emanating from underlying strata, but without expulsion of coal or rock. Methane feeders are further defined as a subset of blowers that continually expend gas over a long period of time but at a lower rate. Many of the mechanisms discussed by Ulery (2008) relate to geologic features that can impound gas within the seam, releasing a voluminous amount when mining breaches the elastic dike, fault gouge, or other geologic structure that had restricted and compartmentalized coalbed methane migration. Thus, the events discussed in this paper can be described as blowers and feeders. However, detailed geological observations of the three longwall mines discussed in this paper appear to indicate a mechanism that is different from those described by Hyman (1987) or Ulery (2008), in that they did not involve coalbed-sourced gas, and the reservoirs were not hosted by coal seams."

Jan 1, 2016

By Daniel S. Mazzei

This paper will be a general discussion of surface flooding considerations as they affect mining facilities site selection, based primarily on experience with several such problems with which MSHA's Bruceton Technical Support staff has been involved. The detailed analytical procedures used in arriving at engineering solutions of these problems will not he presented here; the emphasis is on drawing attention to this additional aspect of mine design which hitherto has been largely overlooked due to insufficient awareness, information and criteria. The paper's purpose is to stimulate thought and offer guidance concerning the selection of sites for mining facilities in light of the potential for flooding problems caused by surface waters. Flooding by surface waters, would generally not be a serious consideration in areas of relatively low topographical relief, i.e. flat lands, although there are exceptions to this rule, for example, in Western areas where flash flooding is a major concern. Therefore, this discussion will mainly apply to areas where the severity of surface flooding would be amplified by the topography-large, well defined watersheds of considerable relief, i.e. mountainous areas. In these regions, steep valley walls cause any rainfall to flow quickly into the relatively narrow valley bottoms. These valley bottoms provide little flow area during storm conditions, so deep and rapidly flowing streams result.

Jan 1, 1982

By Katya V. Babenko, Victor V. Nazimko

We address the problem of the stochastic nature of ground pressure manifestation. Stress distribution in a rock mass and ground irreversible movement are governed with a set of random factors that affect the over-peak strength of the rocks, making them extremely sensitive to any perturbation of the external environment and to internal fluctuations of the thermodynamic state of the rock. We investigate the fluctuation evolution during a longwall face movement to find out whether the fluctuation dissipates or builds up. Five adjacent powered support failures simulate the ground pressure fluctuation. The main roof has been presented as a plate that reposed on the rigid base. The stiffness of the base depends on the thickness of the extracted coal seam and on the dilation of the caving roof. Maximum stiffness occurs in situ, and minimum stiffness is in the gob when the roof is highly flexible and subsides elastically, without caving. The more stress acts in the roof, the higher the cavity that occurs and the larger increment of the base stiffness. The wave of the fluctuation has extended both to the direction of the longwall advance and along the face from the point of the fluctuation agitation. There was an incubation period when the fluctuation was negligible, and the process of the main roof caving remained unaffected. The distance of the longwall advance during the incubation period was twice the longwall length when the fluctuation magnitude was 1% relative to the maximum possible disturbance and 0.76 of the longwall length for the magnitude of 24%. However, the pattern of the roof caving has dramatically changed during further movement of the longwall. All caving parameters have changed: step of the caving, ground pressure distribution, and the manifestation in the longwall and entries. A histogram of the fluctuation magnitude is symmetric in accordance with normal distribution. However, the distribution has abnormal excess. These findings are the first step toward answering the question whether it is possible to forecast the process of main roof caving and weighting consistently. Our preliminary conclusion is that the space and time intervals where this prediction can be made with certain reliability are limited, so further investigation is needed.

Jan 1, 2017

By Wolfgang Schott

The propagation velocity of in-seam seismic (ISS ) waves depends on frequency which is also known as dispersion. This dispersion is not only determined by the thickness of the coal seam and its dirt hand content (i.e. thickness and position), but also by the rock type and its condition (soft or compact) above and below the coal. A coal panel completely surrounded by roadways was investigated using the in-seam seismic transmission survey technique. Along the roadways the immediate roof was either sandstone and shale- The seam thickness varied between 1.20 m (sandstone in the roof) and 1.40 m (shale in the roof) and a fault system (normal faults) crossed the panel with a total throw of about the seam thickness. Below this coal seam another coal scam with a thickness of about 80 cm exists. Its interval shown by exploratory drilling changes from about 60 cm to more than 6 m (scam splitting). Tomographic inversion was applied to the dispersion of the measured ISS waves and velocity distributions were calculated at frequencies found to he most sensitive to changes in the seam thickness and the distance to the coal seam below. By correlating the velocity distributions with known values along the roadways approximate distributions of the coal seam thickness and the seam splitting within the panel were produced. The mining of the coal panel had already been finished and comparison was made between the survey results and the actual situation as far as it was documented. Prediction by the seismic survey was partly in good agreement with the actual held conditions or showed at least the same trends.

Jan 1, 2003

By D. E. Winston

Roof falls are the major cause of fatalities in the, coal mining industry and the prevention of roof failure is a major concern of mine management. Many ground failures observed underground are associated with geological discontinuities such as fractures, faults, clay veins and sandstone channels inherent in the earth's crust (Rinkenberger, 1977). To properly design a mine requires an advance knowledge of such geologic discontinuities and this is not always available from exploration boreholes. The use of remote sensing for mine planning is a relatively new development, and is at present being used primarily by the Roof Control Support Branches of the Mane Safety and Health Administration (MSHA) in Denver and Pittsburgh. However, technical advances, coupled with public access to previously unavailable photographic products, make remote sensing a useful aid in the difficult process of mine planning (Jansky and McCabe, 1979). Remote sensing techniques are being used to predict the location of geological features in advance of mining which influence roof conditions. The features appear on photographic images as linears, which are plotted on a mine map and serve as a planning tool for mine management. Also, during development of entries toward a linear, mining personnel will be on alert for signs of unstable roof conditions which might normally go undetected. Preventive action can then be taken before a fall occurs. A confusing aspect in remote sensing, analyses is terminology such as linear, lineament, fracture trace and joint. In this report the term "linear" refers to a line-like appearance on an aerial photograph or satellite imagery which signifies a naturally occurring geologic feature no the earth's surface. The objective of this paper is to describe the use of remote sensing techniques as an aid in predicting geological discontinuities which might produce hazardous roof conditions to a mine operating in the Pocahontas No. 4 Seam in southern West Virginia. Mine projections and roof control plans will he developed based on this and other available information such as data from cored drill holes.

Jan 1, 1982

By Nicholas P. Kripakov

The unpredictable massive collapse of roof in openings developed under apparently safe and stable roof conditions in coal mines of the United States has been of much concern for many years. One type of massive caving phenomenon is often attributed to cutter roof, a failure that initiates at one and/or both upper corners of an entry and propagates nearly vertically resulting in overall failure with little or no warning. This paper reviews current methods being used to control cutter roof and suggests new alternatives. The impact of basic parameters that include mine geometry, overburden geology, rock properties, and in situ stress conditions is discussed in the context of their relationship to this problem. The effects of various stress control measures are investigated with model analysis to gain insight into means of reducing the high level of stress known to exist at the entry corners of a West Virginia coal mine prone to cutter roof. The results are presented in the paper and the feasibility of their practical implementation is discussed.

Jan 1, 1982

By William J. Schloemer

INTRODUCTION The history of coal mining the Ostrava Region of the Czech Republic goes back nearly 250 years. Both coking coal for steelmaking and thermal coal for the production of energy are mined here; however, it was the coking capabilities that subsequently turned the region into a major steel-producing area in the early 1800?s, something that continues to this day. Ostrava lies in the northeast corner of the Czech Republic, near the southern border of Poland, and falls within the Upper Silesian Coal Basin. The region contains over 400 seams of coal of which about 150 have been mined over its history and continue to be mined. Eighty percent of the Upper Silesian coalfieldlies in Poland and is presently mined by about 35 coal mines; the remaining 20% falls in the Czech Republic, which presently has four mines operated by OKD, a.s., a subsidiary of Amsterdam-based New World Resources. Traditionally, all the mines in this region have employed the longwall method of mining, of which subsidence is an unavoidable consequence. In fact, due to the long history of longwall mining here, there are areas where the overall subsidence has exceeded 37 meters (121 feet). The region is fairly densely populated with residences and industry, and a considerable amount of coal lies under some of these areas where subsidence is not allowed or has to be minimized. It is this reason that has driven OKD to consider alternate methods of mining that will not create subsidence. The decision was made to consider the room and pillar method of mining in order to leave stable pillars of coal to support the surface. After considering several locations, OKD chose the shaft safety pillar at the CSM mine as a test mining location. To say the least, this is a very challenging location in which to conduct a test. As with the entire region, there are many faults from tectonic activity, the seams are pitching at 12 to 20 degrees, the area is affected by high horizontal stress, and the depth of 750 to 900 meters is perhaps the deepest room and pillar coal mining ever attempted.

Jan 1, 2014

By Herryal Z. Anwar

In recent years, many both mining and civil engineering projects are developed in the area which may be categorized unstable, such as fractured and jointed rocks or "water sensitive rocks". For example, in underground coal mining, in which the floor strata normally consist of weak shale, the problem that may arise in roadway is floor heaving. In this case cement injection in borehole appears to be an economically effective method in order to make roadway more stable. This method may be also applied in the projects in which the constructions are laid on fractured and jointed rock. Nevertheless, the successful cement injection is much dependent on the water-cement ratio and the injection technique. This paper discusses the application of cement grouting to improve the ground stability in longwall mining, the laboratory experimentation of cement grouting and the method of floor injection.

Jan 1, 2000

By Liane J. Terrill

A 9O) ft (275 meter) section of a highly fractured beam of halite was mined from the roof of a supported thirteen year old drift at the Waste Isolation Pilot Plant (WIPP). The operation was conducted with a continuous miner and allowed the unique opportunity to collect spatial information on roof beam geology and to observe ground support conditions during the mining advance. Photographs and fracture maps of the mining face document the progress of the operation and the deteriorated condition of the strata. This case study details the drift's excavation and support sequences. the geomechanical response, and the conditions found in the exposed roof beam.

Jan 1, 1997