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By Yongping Wu

Roadway deformation and stress migration occur with uncertainty and randomness because of geology, tunneling and mining influence. In order to study the surrounding rock deformation and failure mechanisms in three-dimensional stress state, an air return roadway of Yuanyang Lake mine of Shenhua Ningxia Coal Industry Group Co., Ltd. was chosen as a research object. The three-dimensional model was a designed and completed experiment with a dynamic-static coupling load. The model was loaded by hydraulic cylinder, simulating the in-situ rock stress field and the induced stress field of surrounding rock. The deformation monitoring system of the roadway model was constituted by optical total stations, borehole observation instruments, acoustic emission monitoring, and stress sensors. A wealth of data was obtained through an omni observation of surface displacement, characteristics of stress distribution, and deformation and failure of surrounding model material. By acoustic-optic-electric methods, a real-time testing on physical, mechanical, and damage parameters was realized through the experimental process. The results showed that the data of deformation and failure obtained from the deformation monitoring system of the roadway were authentic, which has great significance for warning and forecasting safety hazards of surrounding rock in coal mines.

Jan 1, 2013

By Jingyi Cheng

Many longwall panels in China are laid out along the dip direction such that the direction of longwall retreat mining is along the strike direction of coal seams. Downward mining longwall panels in steeply inclined seams refers to those that are laid out in a non-uniformly developed fold structure where the seam is not only steeply dipping, but also highly undulated along the strike direction, causing longwall mining extremely difficult because it has to deal with large dip angles that vary both in the mining and faceline directions. Obviously, the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply dipping seams have unique patterns that are very much different from those cases of mining the flat or gently inclined coal seams. The effects of those unique patterns presented a big challenge to production and safety. Almost all previous and current researches on ground control have been concentrated on issues related to the flat and gently inclined coal seams. Conversely, research on steeply inclined coal seams, especially those with large angle variation both along the seam dip and strike directions is almost none. Therefore, it is very important to initiate a study to better understand the characteristics of mine pressure and overburden strata movement for this special type of geological condition. The objective of this paper is to monitor and analyze the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply inclined seams, the angle of which varies greatly along both the seam dip and strike directions. The measured data has conclusively demonstrated that the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply inclined seams are different from those for the flat and gently inclined coal seams. The large downward angles of coal seam undulation along the strike (mining) direction can obviously affect the roof movement and reduce strata pressure. Study in this research showed that appropriately increasing the rate of mining (or face advance) is positive to roof control.

Jan 1, 2013

By Nathaniel Schaefer, Christopher Newman, Zach Agioutantis

"As mining reserves continue to be developed in deeper and more complex geological and geometric conditions, there has been an increased demand for underground mine designs to better reflect site-specific conditions, measurements, and observations with respect to ground control safety and stability. Current ground control design software are limited to a given device and data files generated can only contain a single design. However, with the growth of cloud computing and increases in internet access, even underground where permissible, web-based software applications allow for in-the-field calculations, as well as collaborations, from multiple users. webGroundControl (webGC) utilizes a multiple-tier architecture, building upon existing NIOSH ground control design software, more specifically ARBS, ALPS, and ARMPS. By providing operators the ability to access ground control design programs from any device, given an internet connection, webGC allows for on demand calculations to ensure underground pillar and roof stabilities with respect to current site-specific parameters, geometries, and geology. Through the development of new features, which aid in design analyses, as well as project collaborations, webGC provides the modern engineer with a more versatile ground control design tool for the improvement of underground health and safety. With the completion of the ARBS, ALPS, and ARMPS modules, this paper introduces potential users within the mining industry to the navigation and operation of the webGC application, as well as its ability to facilitate collaborations between operational personnel and planning engineers. The purpose of this paper is to raise interest in the web-based application before its official launch in Summer 2018."

Jan 1, 2017

By William R. Kohl, Craig B. Clemmens

"Since 2010, North Central Resources, Bridgeport, WV, has been using the sonic log to estimate the rockmechanics properties of the coal and adjacent strata in their exploration drilling program. In 68 out of the 85 boreholes they have drilled since 2010, they have conducted shear wave analysis on sonic logs run in these boreholes. By incorporating the rock mechanics logs into the geological model of the coal seam, the engineers can develop a better understanding of the support requirements for the mine.WellCAD Borehole processing software provides vastly improved efficiency in analyzing shear waves from borehole sonic data than previously available methods. The calculation of most rock mechanics parameters requires knowledge of the density and both the compressional wave velocity and the shear wave velocity. Density logs are well known and an industry standard. Sonic logging is equally well known, although less frequently used, as an accurate source of compressional wave velocity. Shear wave velocity is difficult to measure in a geophysical log, but can be estimated from digitally recorded wave form records. This is a time consuming manual procedure which requires the visual examination of thousands of individual wave forms.WellCAD allows the viewing all the wave forms on a VDL display. The observer can create a pair of false logs by manually tracing the interference points on the display for each receiver. He can check himself by observing wave forms in the traditional format. He can then create a shear wave transit time log or “Delta-S” log by subtracting the false log from the near receiver from that of the far receiver. This can be plugged into standard formulae to generate curves for most standard rock mechanic parameters, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio.While these parameters do not entirely substitute for destructive testing, they are extremely cost effective. An entire borehole can be analyzed for the cost of a single destructive test. This allows for a more judicious use of destructive testing while permitting the extension of test data into the rock mass with much greater confidence."

Jan 1, 2015

By Meng Xiao, Peng Huang, Lizin Lan, Feng Ju, Shuai Guo

"Through changing the axial load on backfilling material compaction test to reflect different overlying strata pressure on backfilling material, the stress-strain relations in the compaction process of backfilling material under the geological condition can be obtained. Based on the characteristic of overlying strata movement in backfill mining, a model of roof thin plate is established. By introducing the stress-strain relation in compaction process into the model and using RIZT method to analyze the bending deformation of roof, the bending deflection and stress distribution can be obtained. The results show that the maximum roof subsidence and maximum tensile stress occurring at the center are 255mm and 5 MPa, respectively. Tensile fracture of roof under the geological condition of Dongping mine did not occur. The dynamic measurement results of roof in Dongping mine verify the theoretical result from the aforementioned model, thereby suggesting the roof mechanical model is reliable. The roof thin plate model based on the compaction characteristic of backfilling material in this study is of importance to research on backfill mining theories and application of backfilling material characteristics.INTRODUCTIONSolid backfilling mining (SBM) is a green mining technology in which the solid waste materials is placed into the gob to support the overlying strata and to control roof's subsidence and movement (Miao, 2012; Miao et al., 2010, 2015). SBM has been successfully used in several mines to solve many problems, including coal extraction under buildings, water bodies and railways, surface subsidence, and environmental problems. Good results have been obtained in many mines (Zhang et al., 2009). The key in the application of SBM technology is controlling strata movement. However, the critical factor influencing the controlling effect of strata movement is compaction characteristics of backfilling materials. Thus, a roof model of SBM is built based on the filling materials' compaction characteristics. A subsidence equation and the critical failure condition of roof was given and field verification was performed at Panel 15061 of Donping Mine."

Jan 1, 2016

By Rusty Mchenry, Craig Dickerson, Robin L. Oldham

"It has been proven that longwall faces can be moved safely and efficiently. However, abutment pressures and poor ground control conditions can halt operations and be hazardous to coal miners. Recently at a mine in Southwestern Pennsylvania, roof material collapsed above shields that created two large voids and caused major challenges for shield recovery. A unique, engineering solution was developed that utilized a modified concrete material to fill the voids, creating stability in the affected area. The many phases of this project included the construction phase, void pumping, cutting out, and bolting of the concrete material. This project eliminated the hazards associated with bolting the recovery face and removing shields in adverse conditions, making it possible for the mine operator to safely complete the longwall move.INTRODUCTIONFrequently in the mining process, especially during the recovery phase, voids above the longwall supports have occurred. These voids are simply roof cavities caused by falling rock strata above the longwall face. Most often, this condition slows down or halts mining operations and creates hazardous work conditions for coal miners. Numerous methods of supporting void areas on longwall faces have been attempted and utilized throughout the mining industry since the advent of the longwall mining system. These methods have utilized many different materials and processes and have included the installation of steel or wooden beams, crib blocks, and various types of roof bolts. However, these methods can be dangerous due to exposure of personnel to the mine voids, falling roof material, and the necessity to handle large amounts of heavy support materials.This paper describes a unique case study in Southwestern Pennsylvania where longwall recovery methods, through two void fills, were successfully completed, eliminating exposure of coal miners to the rock voids above. At the start of this endeavor, normal recovery operations were halted, and hazardous conditions became a concern when the voids were encountered. However, in the interest of safety, the decision was made to try a unique method to completely fill the void from the bottom of the coal seam to the top of the void with a cementitious material and then mine through it. This is in contrast to traditional methods where beams and support materials are used to stabilize the area above and in front of the mine shields, which can expose miners to the void above."

Jan 1, 2015

By Gary Buchan

"Mine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mine operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. The acoustic emissions (AE) form of non-destructive testing has been used for decades to determine material or machine deterioration or potential failure. This paper presents the findings of research in AE with the results of laboratory bolt pull tests and comparisons to field experimentation, including AE sensors and bolt load data in an underground stone mine. The goal of the project is to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of predicting bolt failure or roof deterioration.INTRODUCTIONMine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mining operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. Typical ground control monitoring devices involve drilling into roof or rib, grouting or gluing of sensors, and dedicated cabling for data collection. One of the original goals of this research was to develop a methodology for a simple wireless device that could provide an indication or warning of potential roof bolt or roof failure. Various types of nondestructive testing (NDT) have been used for decades to determine material or machine deterioration or the potential failure of either. One type of NDT is acoustic emission (AE) monitoring, which has been studied for use in mining to predict rock bursts and mine failures since the 1940s (Obert, 1941; Obert and Duvall, 1942). The primary goal of the work was to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of evaluating bolt loading or roof deterioration in an underground stone mine. Bolt pull tests were conducted in the laboratory to establish a repeatable trend of AE activity versus bolt load. The second part of the project was to then install bolt load cells in an underground stone mine and monitor AE activity in the vicinity of mining."

Jan 1, 2018

By Filippo Vallianatos, Michael Verigakis, Vasili Saltas, Kosta Kaklis, Stelio Mavrigiannakis, Zach Agioutantis

"Development of failure in brittle materials is associated with microcracks, which release energy in the form of elastic waves called acoustic emissions. This paper presents results from acoustic emission measurements obtained during three-point bending tests on Nestos marble under laboratory conditions. Acoustic emission activity was monitored using piezoelectric acoustic emission sensors, and the potential for accurate prediction of rock damage based on acoustic emission data was investigated. Damage localization determined based on acoustic emissions evident in the critically stressed region in the form of scattered events or stresses below and close to the strength of the material.IntroductionNon-destructive testing (NDT) has gained popularity in recent years due to commonly available sensors, devices and software tools. Although the majority of such testing still occurs under laboratory conditions, the ultimate goal is a direct field application, especially in the case of underground mining. NDT, if properly applied, may be used to directly provide material property values and characteristics that can be used to determine rock mass or soil mass behavior, with a direct impact to mine design (Iannacchione et al., 2003).AE is generally defined as the high-frequency transient elastic waves originating from the sudden release of energy at localized points within a loaded material (Nomikos et al., 2010). The field of Acoustic Emissions (AE) due to compressive, tensile or other types of loads is a promising research area due to its wide application. The accurate identification of failure precursors stemming from AE is still an open research topic (Lei et al., 2004).Rock is a typically inhomogeneous and anisotropic material that contains several natural defects with various scales such as grain boundaries, microcracks, pores and joint inclusions (Jing, 2003; Read, 2004). Damage induced by microcracks is an essential mechanism in many brittle rocks subjected to stresses. An applied stress induces microcrack growth and damage is distributed uniformly throughout the sample. Finally, the microcracks coalesce and the damage is localized to a shear band, leading to strain softening and macro-scoping failure (Dragon et al, 2000)."

Jan 1, 2015

By Joe Zelanko

In order to prevent roof fall accidents and injuries, U.S. underground coal mine operators must develop and implement effective roof control strategies. Various tools are available to assist engineers in developing designs. For example, criteria to address global stability issues (e.g., pillar stability) are well established in the U.S.; effective tools (e.g., empirical and numerical) are available to diagnose potential problems and avoid catastrophic failures. However, most miner injuries occur as a result of local instability (e.g., a roof fall in a single heading or a rib roll from a pillar corner). Hazard recognition and the availability of support plans suitable to those conditions are key to maintaining stability and safety on the working section.

Jan 1, 2011

By David Miller

Longwall gateroad support can be supplied by a variety of methods. The system of support also needs to be flexible as conditions change. This is especially true in the complex geological conditions of the west Kentucky # 13 seam. Methods of gateroad support used in this seam will be presented along with the successes and failures of the systems as conditions changed Lodestar Energy's gateroad support progression through the seven longwall panels retreated to date will provide an insight into planning for future panels

Jan 1, 1998

By Andre Cezar Zingano

"The empirical approach for pillar design assumes that geological conditions should be perfect, such as horizontal seams, and that pillar strength and behavior will only depend on the coal seam strength and the vertical pressure caused by the overburden thickness on the coal seam; this vertical pressure is based on the tributary area. Empirical methods do not consider the effect of the interface between the roof and pillar or the floor and pillar.The effect of the interface shear strength on final coal pillar strength has been studied since the 1960s. However, few case studies have been generated from that, especially in shallow underground coal mining (less than 100 meters). This case study involves a mining section at the 101 coal mine in the Santa Catarina state of Brazil, which is experiencing pillar rib spalling and yielding because of a 1-to 2-cm-thick clay layer at the area of contact between the coal seam and immediate roof. The depth of the coal seam is 60 m on average and 2.3 m in height. This particular section also has 12-14% (7-8°) of seam inclination. The pillar size varies from l lxll to 13xl2m; thus, the safety factor (SF) based on the ARMPS approach is more than 1.5. The objective of this paper is to determine the cause of the pillar yielding and study the effect of the clay layer at the interface between the roof and pillar, including the inclination of the coal seam. This study conducted empirical and numerical models (2D and 3D) to understand the effect of the thin clay layer. The conclusion is that the clay layer affected the strength of the interface between roof and pillar, causing rib spalling and reducing the pillar strength.INTRODUCTIONPillar stability and deformation depends on the coal seam strength and vertical pressure caused by the overburden thickness on the coal seam, and this vertical pressure is based on the tributary area. The effect of the interface shear strength on the final coal pillar strength has been studied since the 1960s. However, few case studies have been generated from that, especially in shallow underground coal mining (less than 100 m). This interface could be represented by a thin clay layer or an abrupt contact between the coal seam and a rigid sandstone layer of the immediate roof. These two interface conditions are found in the coal mines of Brazil, and the effect of the interface shear strength could increase when the seam's inclination is higher."

Jan 1, 2016

By Kun Li, Shuaishua Yue, Huigui Li, Yuan Ruifu, Yongxiang Xu, Huamin Li

"Coal seams in Tashan Mine of Datong Coal Group in China average 49.2 ft (15m) thick and have been mined by the top coal caving longwall mining method of large mining height. Mining height was 12.5 ft (3.8m) and the top coal caving height was 36.7 ft (11.2m). The gateroad pillar between panels was 124.6 ft (38m). During retreat mining, serious bumps occurred in the gateroads on both sides of the pillar affecting safety production. Therefore, pillarless mining was experimented.Using numerical modeling and comparative study of cases of similar mining condition, it was decided to employ a 19.7 ft (6m) wide pillar, rather than the previous 124.6 ft (38m) wide pillar. Support system for the gateroads was designed and implemented. During gateroad development, pillar failure conditions and entry deformation were monitored. Hydraulic fracturing method was employed to cut off the K3 sandstone along the entry rib so as to reduce the abutment pressure induced during retreat mining. Support reinforcement method combining grouting and advanced reinforcement methods was proposed to insure stable gateroad ahead of mining. Methane drainage and nitrogen injection were implemented to eliminate hazards associated with mine fire and spontaneous combustion.Since the development of gateroad has just completed, and retreat mining has not begun, the effectiveness of the proposed methods is unknown at this point. However, monitoring will continue until after mining. The results will be published in a separate paper.INTRODUCTIONGeneral descriptionTashan mine is located about 15 Km south of the city of Datong, Shanxi province, China (aure 1). The 2014 raw coal production was 25 million mt."

Jan 1, 2015

By Zhikai Wang, Wensheng Lyu, Peng Yang

"To better understand the mechanical behavior of the compression deformation of backfill under high stresses corresponding to large depths, consolidation compression tests were performed for cemented tailings backfill with a cement-sand ration of 1:10 and 30% water under confined conditions. After applying different loading stress functions from 0.5 MPa to 32 MPa, the final axial deformation of the test specimen of backfill was obtained, and the micromorphology of backfill was studied before and after consolidation by scanning electron microscopy. Additionally, fitting analysis was performed for backfill confined compression deformation data and device model constitutive equations by the minimum square law. The constitutive model was revised according to the analysis results. The research results indicate that, as the load increases, the void ratio e obeys the functional relationship e=alnt + b (where a and b are fitting constants and t is compression time). Under the high-stress conditions of confinement, the constitutive model of backfill consolidation and creep can be used to describe the creep behavior of the backfill. Under high-stress conditions, after the consolidation of the confined backfill, the space between the tailing particles diminishes, the particles becomes more compact, and particle slippage occurs. INTRODUCTION With the depletion of shallow mineral resources, the mining industry has gradually shifted to deep mining (Zhang, Li, An, and Huang, 2010). Furthermore, with the continuous introduction of sustainable development policies regarding development and utilization of mineral resources, the mining industry must protect the limited available land and make full use of mineral resources as much as possible (Sijing, 1994; Zhihua, 2009). Backfill mining technology offers an unparalleled advantage in fully recovering mineral resources, controlling pressures, and improving environmental protection. As a result, this method has been widely used in various countries in the world (Burd, 2002; Benzaazoua, et al., 2008). Of the underground mines in the world, 45% of the large and medium-sized non-ferrous-metal mines and 37% of the gold mines use backfilling (Fuhrman, et al., 2014; Khaldoun, Ouadif, Baba, and Bahi, 2016). In addition, 45% of underground non-ferrous-metal mines and 37% of the gold mines use the filling method (Mchaina, Januszewski, and Hallam, 2001). According to incomplete statistics, more than 80 metal mines operate at a depth of more than 1 km; the depths of several typical deep mines are shown in Figure 1 (Burd, 2002; Fall, et al., 2009)."

Jan 1, 2017

By Tony Iannacchione

A close look at the Loyalhanna Limestone of southwestern Pennsylvania reveals a complex structural environment. Most exposures of the Loyalhanna occur along Chestnut Ridge and Laurel Hill within the Allegheny Mountain Section of the Appalachian Plateaus Province. Because the Loyalhanna is rated as a super pavement aggregate by the Pennsylvania Department of Transportation and because of its proximity to the population centers of southwestern Pennsylvania, the Loyalhanna has been extensively mined along these prominent anticlinal structures. Geologic and engineering analyses were performed using gas well and core logs, outcrop examinations, underground observations, and mine maps. Strata exposures from both outcrops and quarries were used to construct geologic maps, stereonet, and rose diagram projections so that the Loyalhanna's structural environment could be understood better. Many of these structural conditions cause ground control problems at local quarries. These problems ranged from small-to-moderate sized rock falls associated with roof jointing to pillar failures associated with dipping discontinuities. Stresses ranged from tensional on structural domes where weathering dominates, to high levels of compression within structural saddles. A greater understanding of these characteristics is a prerequisite to develop engineering controls, such as improved mine layouts. pillar sizes, etc., that lessen miner exposure to these hazards.

Jan 1, 2002

By Houquan Zhang, Ming Li, Guimin Zhang, Bei Zhang

"The support quality of bolts in deep roadways is one of the important factors for efficient and safe coal production. A new kind of non-destructive testing technique and equipment was used to monitor the axial bolt load in real time in deep roadways. Based on the test results, the working status of bolt support in deep roadways was evaluated. The research results show that the variation characteristics of axial bolt load is consistent with the distribution characteristics of rock pressure no matter whether it is in the initial support stage or mining disturbance stage. The axial load of bolts located 20m outby the development face has an overall rising trend within 3-5 days after installation. Within a certain distance in the front abutment pressure zone in front of the face, the axial bolt load increases with the advance of coal extraction. When coal and rock in the abutment pressure zone yield, the axial bolt load is dropped correspondingly. This kind of non-destructive testing technique provides an advanced means of detection and evaluation on bolt support quality.INTRODUCTIONMany coal seams more than 800m deep are being mined in eastern China. Roadways of large cross-section are being developed in coal seams more than 600m deep in western China (Kang et al. 2014). Moreover, these roadways are commonly supported by roof bolts and have encountered many support problems, including soft rock strata, intense mining disturbance, and abnormal tectonic stress. The stability of its surrounding rocks is difficult to maintain, the roof bolt even fails before mining (Shen 2014; Jiang et al. 2015). Therefore, it is very important to develop an effective method to detect the bolt quality in real time and evaluate the bolt's safety status.During installation of roof bolt, the installation quality is heavily affected by installation equipment and tools, field conditions, and operators' skills (Li et al. 2005; Shan 2009). The anchorage length will be shorter than the designed one if the resin cartridges are pushed to the bottom of excessively long drill hole and stay there without being shredded and mixed. The support function of the bolt would be weakened by the shorter anchorage length."

Jan 1, 2016

By Liang Dong, Jinxuan Liu, Biao Qiu, Jing Chai

"The Cenozoic unconsolidated strata in the east area of China are composed of clay, sandy clay, fine sand, hardpan, etc. Numerous shafts of the coal mines in these areas have been damaged in various degrees since 1987. The main reason for this disaster is the vertical additional stress on shaft caused by the subsidence of the thick unconsolidated strata. In order to monitor the subsidence deformation of the unconsolidated strata, a sensing network system with multiplexed Fiber Bragg Grating (FBG) for monitoring settlement deformation of the unconsolidated strata in deep borehole is proposed. The field monitoring results show that, soil layers settle or expand with decrease or increase in ground water levels. The thick hardpan generates the main compressive deformation. This FBG strain monitoring method can take place of traditional ground water measuring method. This system is stable and reliable, and the monitoring results can show the subsidence deformation of different layers, which has significance for the predictive maintenance of the shafts.INTRODUCTIONSince 1980s, a specific geologic hazard has occurred frequently on the coal mine shafts in eastern China: non-mining-induced shaft deformation, involving up to 100 shafts located in Jiangsu, Shandong, Anhui and Herran province, distributed in Xuzhou, Datun, Huainan, Huaibei, Yanzhou and Yongxia coal fields. This kind of geologic hazard can lead to shaft wall deformation, water infiltration, cage stuck, water-sand burst or shutting down of coal mines, which seriously risks the coal mines. Zhangshuanglou coal mine, Haizi coal mine and Linhuan coal mine shut down for 2-8 months due to this hazard (Chen, 1997; Cui, 1998). The main reason for this geologic hazard is the subsidence of the super thick unconsolidated strata (Liu et al., 2007; Xu et al., 2006).An innovative structure health ·monitoring and damage estimation method has been developed in recent years, i.e., optical fiber smart material and structure (Nobuo, 2002; Wang et al., 2000). A Fiber Bragg grating (FBG) sensor is a device that can transfer the change of the measured strain or temperature to the change of Bragg wavelength. One of the most important applications of FBG sensors is to monitor the internal stress and strain distribution of material and structure (Philipp et al., 2000; Ansari et al., 1998). Compared to traditional electrical sensors, FBG sensors have many advantages; they are adaptable to harsh environments, abrasion resistant, immune to electrical magnetism (EM) interference, safe and reliable. They also offer integrated sensing and transmission on a single fiber, have simple structure and are convenient to use, which satisfies the requirements of long distance, distributional and long term use in monitoring mining and geotechnical engineering structure. Due to such advantages, the FBG sensor has already been applied in petroleum engineering (Kersey, 2000), rock mechanics testing (Cornelia et al., 2003; Yang et al., 2007; Wei et al., 2008), physical simulation experiments (Chai et al., 2007; Chai et al., 2006; Zhu et al., 2008; Li et al., 2008; Chang et al., 2008), strain sensor (Li et al., 2007; Chai et al., 2008) and construction structure damage diagnosis (Dong et al., 2004; Kerrouche et al., 2008; Whitten et al., 2001)."

Jan 1, 2010

By Morgan Sears

The LaModel program (Heasley, 1998) is a displacement discontinuity, boundary element model (BEM) for analyzing stresses and displacements in single and multiple-seam coal mines. After the Crandall Canyon mine collapse, the need for better design guidelines for LaModel was observed and a new calibration method for deep cover pillar retreat was developed (Heasley et al., 2010). However, the scope of this initial calibration was limited to single-seam mines deeper than 750 ft. This limited application of the initial calibration method lead directly to the research presented in this paper, which attempts to define appropriate LaModel calibration guidelines for pillar design where shallow cover and/ or multiple-seam mining scenarios are encountered. As part of this research, a database of shallow cover case histories has been developed, and this database is used to help validate the shallow cover calibration method. By adding the shallow cover database to the previous deep cover database, the LaModel calibration method has now been extended to the complete range of mining depths, as well as to multiple-seam cases. With this shallow cover calibration, the utility of the LaModel program continues to increase.

Jan 1, 2013

By S. Paul Singh

"The long-term viability of seismically active and/or deep mining operations hinges upon the industry's ability to maintain profitability in a climate of increasingly difficult conditions, escalating operating costs and fluctuating metal prices. Within this context, it is prudent to explore mining techniques that could provide means for safer and more profitable extraction of seismically active and/or deep seated deposits that are vital to the long term survival of the industry.The first step was to examine Penetrating Cone Fracture (PCF) and other relevant concepts with the objective of semi-continuous mining in deep underground hard rock mines. This was followed by an assessment of the current conventional drilling and blasting practice. Thirteen blasts were monitored in five different seismically active workings of an operating deep mine. The main concerns during the current drill and blast practice were identified.On the basis of the literature review, three short round blasting techniques were short listed for further review. These techniques were evaluated based upon the available literature and discussions with the persons associated with their applications. Justification, requirements and major challenges for the application of short round blasting have been discussed in this paper. Suggestions for improving the current drilling and blasting practice have also been outlined.INTRODUCTIONRock fragmentation is the key to mineral excavation and production. Increasing working depths, environmental concerns and trends towards continuous mining necessitate the development of new and improved rock breakage methods.The excavation of hard rocks is still dominated by the sequential routine of face preparation, drilling, charging explosives, blasting, ventilating for fume and dust removal, mucking and roof support. Worse still, drilling and mucking require specialized equipment that fills the end of the heading so that no other operation can be performed and the equipment must be removed from the face to protect it from fly rock."

Jan 1, 2010

By Jonathan Duncan, Tim Burgess, William Kendall, Jens Lange

"Steel wire mesh is the accepted standard for roof and rib skin control at most coal mines in the United States. Wire mesh is delivered to the mine in bundles that are heavy and awkward to handle. The large size, stiffness, and weight of the wire mesh can present a safety hazard in transporting underground and storing on the roof bolter. Installing wire mesh on the roof and ribs with the roof bolter can be a challenge as well.Synthetic mesh is lighter than wire mesh and can be folded and rolled into a safe, manageable size. A single synthetic mesh roll large enough to cover the roof and ribs in a deep cut can be safely handled by two men. The roof bolter is designed to carry and dispense the roll as it advances and installs primary roof support, resulting in a single pass roof and rib ground control solution. This paper focuses on the design and implementation of the roof bolter synthetic mesh handling system developed by J. H. Fletcher & Co., Huesker, Inc., and Oxbow Mining.INTRODUCTIONRoof and rib skin control in some coal mines has been an issue since mining first began. Roof and rib skin problems vary from mine to mine. The type of roof rock material exposed after mining; the mine atmosphere; and stresses from depth of cover, over mining, and/or undermining are some of the variables that can contribute to roof skin problems from mine to mine.Potential roof and rib skin problems can be time dependent as well. Some mines have roof skin rock, sometimes called draw rock, that falls when drilling the hole for the roof bolt as the initial roof support is installed. Some roof skins are more stable but can fail over time. The failure of roof skin can even be between properly installed roof bolts with roof plates (Figure 1).Mines have most commonly used a wire mesh that comes in individual panels anywhere from 5 ft x 5 ft (1.5 m x 1.5 m) all the way up to 5 ft x 16 ft (1.5 m x 4.9 m) in size. They are typically constructed of 8- or 9-gauge wire welded on a 4 in (102 mm) square pattern. A 5 ft x 16 ft (1.5 m x 4.9 m) panel weighs approximately 35 lbs (16 kg). These steel wire mesh panels can make it a difficult and sometimes dangerous task to deliver them from the surface to the roof bolter and then store on the machine. Manipulating the mesh panels from the storage area on the machine to the final installation position on the roof or rib can also be a daunting task (Figure 2)."

Jan 1, 2010

By Anthony Iannacchionc, Jessica Benner, Harold Miller, Megan Witkowski

"Longwall bituminous coal mining has been practiced in Pennsylvania since the 1970""s. Hundreds of longwall panels have been mined during the last 40 years but only 24 have actually undermined Pennsylvania's Interstate Highway System. The impact to interstate highways are summarized in this paper and the factors that influence the magnitude of these impacts are examined.INTRODUCTIONOver the last 30 years, interstate highways in Pennsylvania have been undermined by portions of 21 bituminous coal mine longwall panels. From 2003 to 2008, three of the panel were extracted by the Emerald Mine and six by the Cumberland Mine both in Greene County and both owned by Alpha Resources. Previous assessments of longwall mining under Pennsylvania’s interstates have identified impacts to the highways but no danger to public safety. In general the magnitude and extent of impacts during the recent undermining of Interstate 79 or 179 appears to be similar as those identified in previous studies. The nine longwall panels are among some of the widest in the U.S. They are supercritical in character with overburdens ranging from greater than 152 m (500 ft) to less than 305 m (1,000 ft).The Pennsylvania Department of Environmental Protection (PA DEP) requested that the University of Pittsburgh summarize observations collected by their staff during the recent undermining of 179. Observations and photographs of impacts to the highway were made by PA DEP staff and entered into reports prepared by California District Mining Office (COMO) staff and statements written into the Bituminous Underground Mining Information System (BUMIS) database. In addition to the observations by the PA DEP, the Pennsylvania Department of Transportation (PennDOT) conducted a series of detailed land surveys along portions of the highway undermined from 2003 to 2008. To characterize the subsidence basin fanned by longwall mining. PennDOT information has been analyzed by another research group within the university (Guticrre7, et al., 20 I 0)."

Jan 1, 2010