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By Mikko Ahola

This paper describes recent innovative analyses conducted by the Bureau of Mines to demonstrate the application of the boundary-element method in evaluating the effectiveness of caving chambers or sacrificial entries to relieve the stress conditions initiating cutter roof failure in underground coal mines. The analysis assumes that cutter roof failure results when the shear strength of the roof rock at an entry corner is exceeded by the applied shear stress. The applied shear stress is due to large differences between the horizontal and vertical in situ stresses known to exist in many coal mining districts experiencing cutter roof failure. The results of boundary-element analysis suggest that driving an arched lead entry in advance of adjacent rectangular entries and allowing it to cave significantly reduces the difference between the principal stresses at the corner of the rectangular entry, thereby lowering the maximum shear stress. Slippage of the immediate roof along horizontal bedding planes into the caved entry is shown to further reduce the stress conditions in adjacent entries. Practical applications of this stress control technique to longwall and room-and-pillar mining are discussed.

Jan 1, 1987

By Chris T. Franke

The Waste Isolation Pilot Plant is a deep underground facility mined in bedded salt interspersed with persistent clay inter- beds. The clay seams delineate beams of salt above and below the excavations which strongly influence excavation performance. This paper reviews available rock mechanics information relevant to improving drift stability by removing the roof beam. Conceptual deformation mechanisms, relevant field data, and numerical analyses were used to investigate the effects of mining the roof of the excavations along a clay seam. Finally, a case study that applies the results of this investigation is presented.

Jan 1, 1997

By Frederick Carr

1. The application of retreat longwall mining to the North American coal mining conditions is be¬coming more advantageous as more experience is gained. The productivity results being achieved and potential possible illustrates that this system can be the keystone of future underground coal production. 2. In the American coal fields multi-entry is normally practiced as this allows profitable longwall development with existing equipment and systems. Difficulties are being experienced however in the longwall retreat phase by the col¬lapse of multi-entry roadways and excessive use of supplemental support in the following panel tailgates. In some instances the headgate of an operating face can also be in difficulty. 3. Jim Walter Resources Mining Division is developed on a mining plan that calls for three retreat longwalls at each of its four deep mines which have varying depths of cover and immediate roof and floor conditions. The #3 Mine has experienced longwall entry difficulty and there were differing viewpoints with respect to the best development systems to adopt particularly regarding the number of entries and pillar sizes. In an attempt to reconcile these different points of view J.W.R. asked Dr. Wilson to examine the problem and this paper outlines the new approach developed.

Jan 1, 1982

By Peng-Fei He

CT scanning tests were used to detect the pre-existing fracture systems of 36 cubical coal blocks. Systematic procedures were developed to construct the pre-existing fracture geometry of the cubical coal blocks from the CT images. Based on the constructed fracture systems, the fracture tensor components were calculated to capture the directional effects of the fracture system of the cubical coal blocks. The effect of the pre-existing fracture system and different combinations of confining stresses on the strength and deformability of coal masses was investigated at a preliminary level using some true triaxial test results and the computed fracture tensor components. The strength of the cubical coal blocks in the loading direction was found to be closely related to the summation of the fracture tensor components in the two perpendicular directions to the loading direction and the level of the confining stress system. The deformability of cubic coal blocks in the loading direction was found to be correlated to the fracture tensor component in the same direction.

Jan 1, 2014

By Andrew Lewis, Amarit Nitaramorn, Alexander Garcia, Peter Altounyan

"Indonesia is a major coal producer, the vast majority being sourced from opencast operations. Underground production to date has been constrained by unfavorable ground conditions and limited local experience. However, an underground trial in East Kalimantan has now shown that it is possible to successfully extract coal and mine safely, despite the technical challenges.A trial drift mine has been worked to a current maximum depth of 160 m (525 ft) in a dipping coal seam. The 3 m (10 ft) thick coal seam is overlain by very weak mudstone and sandstones. The mudstone forming the immediate seam roof strata proved a particular challenge given its adverse reaction to water and overall friability.Rock bolts were used as roadway support, the system being carefully selected to optimize effectiveness. An innovative method of partial extraction was trialed, which demonstrated the potential for productive mining despite the ground conditions. Roof falls have occurred within the working area, and roadways demonstrate reasonable stability over time.Throughout the course of the trial, strata behavior monitoring has been an important aspect, and a comprehensive ground control monitoring system is in place. This has enhanced the ability to increase the level of support where required and to react to deteriorating conditions. In addition, monitoring information has allowed a quantitative assessment to be made of the technical feasibility of future full-scale mining.INTRODUCTIONWith current production at over 200 million tons, much of this destined for overseas markets, Indonesia is the second largest exporter of coal (Ritschel and Schiffer, 2007). The majority of the coal is sourced from the Kalimantan coalfields. Mining is predominately opencast, yet in recent years there have been attempts made to introduce underground operations. This move would permit continued access to good quality seams that are beyond the reach of viable opencast mining."

Jan 1, 2010

By Kazem Orace, Navid Hosseini, Mehran Gholinejad

"Selection of the optimum support system for underground openings such as tunnels is a complex process. In this paper a new approach, based on a combination of the Analytical Hierarchy Process (AHP) the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and the Preference Ranking Organization METHod for Enrichment Evaluations (PROMETHEE), is introduced. For this purpose, the selection process is assumed to be a multi criteria decision-making problem. First different support systems using FLAC3D numerical code, based on technical safety and stability parameters of the tunnel are specified. Then taking economic and performance parameters as the decision criteria by using the combination of Al-IP, TOPSIS, and PROMETHEE the optimum support system is selected. As a real mine case study this approach is used in the main access entry to the C, coal scam of Tabas collieries. Results clearly demonstrate that the proposed support system selection method is more advantageous than other alternatives.INTROD CTIONGenerally, the support system for a tunnel is selected primarily with the aid of design engineers experience. In other words personal judgment instead of intellectual and scientific criteria is mostly the main basis (Oracc. 2005). However since various support systems can be applied in any particular situation, accurate selection of the optimum support method depends on the integration of many technical, economical and performance parameters, and also on the analysis of the intensity of influence by each of the criteria.In this paper an applicable approach for se lection of tunnel support systems based on Multi Attribute Decision Making (MADM) techniques including: Al IP (Orace et al.. 2009a; Saaty, 1980), TOPSIS (Hwang and Yoon, 1981: Yoon and Hwang, 1995), and PROMETHEE (Brans and Vincke. 1985; Brans and Mareschal. 1992) is introduced. As a field study, this approach was applied to tunnel C1 as one of the main entries in the Tabas coal mine which is the major collieries in the central pan of Iran (Hosseini, 2008).Due to the coal seam conditions coal is mined by mechanized longwall mining (Hosseini 2008). This method requires the 58 excavation of several entries some of which will be used for many years and even for the entire life of the mine (Peng, 2006). Therefore the selection of the support system in these entries is·very important in mining design."

Jan 1, 2010

By Dennis R. Dolinar

Roof falls, even of supported roof, still constitute a major hazard in underground mines. However, associated with any fall or instability is a pattern of roof movement. Therefore, the National Institute for Occupational Safety and Health, Pittsburgh Research Center, has been conducting research into the development of practical extensometer systems that can be used to measure this displacement and to determine if a roof fall may occur, thus increasing miner safety. For extensometers to be used in the detection of potential roof falls in coal mines, an understanding of the movement and displacement rates that will lead to roof failure is required. Because roof falls are unpredictable, it is often very difficult to obtain this information. Therefore, in a coal mine in the lower Kittanning seam in Pennsylvania, a room widening experiment was conducted to intentionally cause a roof fall while roof movement data was collected. In this experiment, two adjacent rooms 5.5 m (18 ft) wide supported with 1.5 m (5 ft) resin-grouted bolts and instrumented with extensometers were widened to 9 m (30 ft). In one of the rooms, 3.6 m (12 ft) cable bolts were installed as supplemental support. In the room with no additional support, a roof fall occurred 72 h after the room was widened. Much of the 3 cm (1.2 in) of movement in this room resulted from the instantaneous and transient response to mining with displacement rates up to 7.6 cm/d (3 in/d) being measured. This was followed by a steady state displacement phase with a rate of 0.43 cm/d (0.17 in/d). Just 12 h before the fall, movement deeper in the roof caused the rate to accelerate to 1.1 cm/d (0.44 in/d). The roof in the room with the supplemental cable support did not fall even though the total roof deformation was over 7.6 cm (3 in). Significant roof movements and strains in the cabled room were detected to a depth of 3 m (10 ft) while maximum cable loads were over 180 kN (40,000 lbf). Essentially, the roof was in postfailure with the cables maintaining the material, while roof stability was indicated by a steady state displacement rate of only 0.025 cm/d (0.01 in/d) at the end of the test.

Jan 1, 1997

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

By Chris Kelly

The Monroe County Quarry is an open pit granite quarry located near the town of Bolingbroke. Monroe County. Georgia. The quarry has been in continuous operation for approximately 10 years. The quarry covers approximately 27 acres and has an annual production rate of 1.0 million tons. On the morning of April 26. 2000 a sudden rapid highwall failure occurred at the west end of the north wall of the quarry pit. The failure occurred approximately one hour after a three inch-wide crack was observed in an access road located at the crest of the highwall. No indications of failure had been observed prior to the development of the crack. The active mining area had been at the base of the failed area. The pit was successfully evacuated prior to the failure and there were no losses of either personnel or equipment. The amount of failed material was estimated to be in excess of two million tons. In order to ensure a safe working environment at the quarry a slope monitoring program was established in the area of the failure. The program consisted of using an EDM survey instrument to periodically measure the location of survey prisms installed at carious points on the north wall. The locations of the prisms were recorded over several months and changes in location were analyzed in order to identify and characterize the movement of the failed mass. The results of the analysis provided a basis for recommendations regarding access to various areas of the quarry. This paper discusses the factors contributing to the failure, the method of post-failure slope monitoring, anti the interpretation of the monitoring data.

Jan 1, 2002

By John R. Poland, Benjamin Mirabile

"There are significant ground support hazards to both personnel and equipment when longwall equipment must mine through cross-panel entries. Backfilling support strategies are often cost prohibitive. Additionally, it is often very difficult to install backfill material in full contact with the mine roof in backfilled entries. This paper will demonstrate the use of fiber-reinforced concrete crib material as a method for standing support in longwall cut-through entries. Despite conceptions of poor performance in potentially high convergence environments, fiber-reinforced concrete crib material can be used in longwall support environments subject to high abutment loads and convergence. Central to the proper design of these supports is the use of yield material between crib layers and at the mine roof/crib interface. The placement location of cribs within the cut-through entry has a significant effect on the main roof behavior and associated ground conditions in the longwall abutment zones. It is particularly important to engineer the proper load displacement characteristics of the installed crib to support expected ground conditions. The cost of fiber-reinforced crib supports is less than 50% of backfilling methods.INTRODUCTIONThe design and execution of a longwall cut-through is perhaps one of the most difficult and risky endeavors in the field of ground control. The magnitude of abutment loads and potential for ground failure present a significant safety hazard to underground personnel. In addition, there is significant financial risk, with replacement costs of face equipment exceeding $200 million. Faced with these consequences, it is both advisable and common for an engineer to design ground support with a significant margin of safety. This paper outlines a robust support system that possesses a significant margin of safety along with significantly lower costs than most other support systems employed in similar conditions.SITE PARAMETERSThe mine site described in this study operates in the Herrin No. 6 seam in southern Illinois. The seam height is typically 76- 84 inches. Mining height in gateroads and mains is typically over 96 in, and typical mining height on the longwall face is 82 in. The overburden depth is 950-970 feet in the area of the longwall cutthrough."

Jan 1, 2016

By Ed Van Eeckhout

As part of a U.S. Bureau of Mines-sponsored project on the utilization of "stiff' backflll to minimize potential rock burst hazards, a finite element study was undertaken to predict stresses and displacements around a stope mined up from the 5400 level of the Sunshine mine, Kellogg, Idaho. This stope was to be backfilled using a high-modulus fill. In preparation for that configuration, certain instrumentation was installed near the 5400 level to monitor stress changes. Due to untenable economics, only 2 cuts of the stope were ever made. This paper presents the results of the instrument readings taken during the first cut and compares them with the numerical predictions, as well as presents the modeling results of closure and fill stresses in the stope if it had been mined.

Jan 1, 1984

By Wojciech Masny, Andrzej Walentek

"The most common extraction method in Polish coal mines utilize pillars between adjacent longwall panels. This is mainly due to the significant depth and difficulties in maintaining stability of the gateroads. This paper presents measurements of entry convergence and range of the fracture zone around a gateroad measured with a borehole camera. The entry where the measurements were taken was located in a parallel entry separated from the gateroad by a 5-m- (16-ft-) wide pillar. The gateroad was located in a hard coal seam 900 m (2,952 ft) deep with a dip of 5°. The extraction method was longwall mining with caving and the mining height was about 3 m (10 ft).Furthermore, the ""in situ"" measurements were compared to the convergence forecast for the gateroad and fracture zone by means of numerical modeling conducted using the Phase2 Version X.X finite element program from Rocscience. The determination of the fractured zone around the openings is of great importance to successful mining practice, especially in support planning and design for longwall gateroads. Moreover, proper determination of the fractured rock zone is one of the basic elements in the process of planning the roof bolting for mine workings.INTRODUCTIONIn the Polish. hard coal mining sector, retreat longwall extraction is most commonly used (Prusek and Masny, 2007). This method is connected with the necessity to carry out a number of development operations during the first stage, including among others, driving of gateroads and a setup room.Currently, most Polish mines eliminate gateroads behind the extraction front, using the ""U"" ventilation system (Szlitzak et al., 2008). In such cases, one of the roads for the next longwall panel is driven along the caving goafs, leaving a protective pillar of some chosen width (Figure 1). The question regarding the width of the coal pillar is especially important to the stability of the gateroads that define the panel for the subsequent longwall. When analyzing the previous experience relating to this type of pillar (Junker, 2006; Rajwa, 2008; Stranzet et al., 1973; Betriebsempfehlung, 1982), one can state that there exist two solutions for the determination of its width."

Jan 1, 2010

By Essie Esterhuizen, Michael M. Murphy, Chris Mark

"The design of underground coal mines requires a clear understanding of the overburden response, the loading of pillars, the loading of the gob, the pillar failure process, and the ultimate load carried by partly or fully yielding pillars. Very few highquality stress measurements of yielding pillars and gob loading have been made in full extraction mining. Well-calibrated numerical models can assist in providing a better understanding of the load and failure processes, provided the coal, the overburden, and the gob are all modeled with sufficient realism. A program of numerical model calibration and validation was carried out using FLAC3D.1 The models were calibrated against observed and measured performance of coal pillars and the overburden in operating mines to provide a basic set of input parameters that can be used to provide a realistic first estimate of expected ground response and pillar loading. Input parameters for modeling coal pillar response were based on data from triaxial testing on coal samples, combined with both matching the depth of failure in the coal ribs to observations as well as matching the peak pillar resistance to an empirical equation. The models were calibrated against strong roof and floor case histories in which the pillar strength is governed by failure and yielding of the coal within the pillar and the surrounding strata only had a limited impact on pillar strength. Input parameters for the overburden were determined from a large database of laboratory tests and model calibration against maximum subsidence and subsidence curvature. Further overburden calibration was carried out by matching stresses in the mining horizon to field measurements. Three examples of the application of the calibrated dataset and modeling methodology to field measurements are presented. The results show that a reasopable estimate of the in-seam stress distribution and overburden response can be obtained for both strong and weak overburden scenarios at various depths of cover.INTRODUCTIONThe planning and design of coal mine excavations requires reliable estimates of the expected strength and loading of the mine structures to achieve global stability. Empirical methods are widely used to estimate the strength and loading of coal pillars and have been incorporated into pillar design procedures, such as Analysis of Longwall Pillar Stability (ALPS) (Mark, 1987) and Analysis of Retreat Mining Pillar Stability (ARMPS) (Mark and Chase, 1997), that are widely used in the United States. ~umerical models are finding increasing application as a tool for underground mine design because of their. versatility and the ever increasing computational power available to mine designers. A prerequisite for the application of numerical models is the calibration of the models against observed rock mass response (Hoek et al., 1990; Skiles and Stricklin, 2009). The calibration process may include comparison of model results to measured stress and deformation and modifying the input parameters in a systematic manner to achieve a satisfactory agreement between the model results and measurements. Once models have been calibrated, they can be applied to evaluating similar mining layouts in similar geological conditions."

Jan 1, 2010

By Dakota D. Faulkner

Cable bolts anchored with traditional two component polyester resin cartridges have successfully supported difficult roof conditions in underground mines. Resin cartridges provide a costeffective cable bolt anchoring system with consistent anchorage performance characteristics when properly installed. The most commonly used cable bolts in the U.S. mining industry are 270 ksi (1,862 MPa), 0.7 and 0.6 inch (18 and 15 mm), seven-strand smooth cable with resin mixing bulbs (also known as bird cages), and 40- and 30-ton nominal capacity, respectively. However, there are other types of cable bolt anchoring systems aside from bird cages. Recently, many questions have been raised regarding the anchorage characteristics of various types of cable bolts. Keystone Mining Services, LLC (KMS), the affiliated engineering company of Jennmar Corporation, conducted a variety of controlled tests developed to closely model actual underground installations. These tests compared the performance of three commonly used cable bolt varieties, including plain, bird caged and indented seven-strand cable. Details of the laboratory testing and comparative analysis of the results are provided.

Jan 1, 2013

By Takashi Sasaoka, Hiroshi Takamoto, Akihiro Hamanaka, Pongpanya Phnthoudeth, Hideki Shimada, Jiro Oya

"Indonesia is the second largest coal exporter to Japan, accounting for about 30 Mt annually. They produced over 400 Mt in 2015, over 99% of which is from open-cut mines. However, the conditions of surface mining are becoming worse year by year: the stripping ratio is increasing, the economy is worsening, and the infrastructure for coal transportation from inland mining areas is not being maintained. To meet the demand for coal in Indonesia and the rest of the world, underground mines have to be developed. In consideration of growing need, our research program is conducting a study on the potential for an underground coal mine in Indonesia. This research is being done through the roadway heading research program, which is looking into developing an underground coal mine from an open pit highwall. The greatest challenge for underground coal mine development in Indonesia is the maintaining the safety of the mine roadway during heading because the roof rock is exceptionally weaker. There is a potential for heading below mobile, unconsolidated soft sediment, and instead mining a deep area. This increases the likelihood for problems in the stability of the support system due to increasing ground pressure. The ground behavior around the roadway was measured using telltales, extensometers, and convergence measurements. Moreover, rock property tests were also conducted on exploration drilling cores. Based on the geological dates and monitoring data, a series of numerical analyses were conducted in order to assess support needs in the main roadway under different depths. Results of numerical analyses indicate that the current arch support design is effective when the mining depth is lower than 100m. However, if the mining depth is larger than 100m, the current arch support design should be changed to include the application of higher yield strength material, shorter spacing, etc. Moreover, bolting may also be useful if ground pressure is high locally. Based on a series of measurement data of ground and support behavior, a control criterion for main roadways under weak geological conditions is proposed in this paper."

Jan 1, 2017

By Mark F. Sindelar, Yi Luo, Hua Jiang, Michael T. Shook

"Convergence of roof and floor in underground mine openings is a common occurrence. This convergence not only adversely affects the ability of workers, equipment and supplies to travel through the mine, it also reduces the effectiveness of the mine ventilation system, which is essential for the dilution of methane gas and airborne respirable dust. While installing secondary standing supports to control floor and roof convergence, such supports, by nature, partially obstruct a portion of the airway. These added obstructions inhibit the ability of the ventilation system to operate as efficiently as it could by increasing the resistance in and reducing the cross-sectional area of the airway.This study introduces and demonstrates the benefits of The Eye CAN™ standing roof support, which controls floor and roof convergence and is less obstructive to air flow than conventional wooden cribs. Laboratory findings show that the normal resistance of a supported lined airway is reduced by using this new product from Burrell Mining Products, Inc., while providing the same roof support characteristics of an established product-The CAN®. Load vs. displacement curves generated from laboratory tests demonstrated that this new product behaves with the same roof support characteristics as others in The CAN product family. Ventilation data gathered from a simulated mine entry was then used for computational fluid dynamics (CFD) modeling. The CFD analysis showed an improvement with The Eye CAN versus other accepted forms of standing roof support.This proof-of-concept study suggests that, when using this new product made by Burrell Mining Products, Inc., not only will the convergence from the roof and floor be controlled, but airway resistance will also be reduced.INTRODUCTIONOne of the basic elements of underground mining is the necessity to support the mine roof. It is well-known that easier reserves have been mined so that today's underground mines present challenging conditions. Factors influencing roof support decisions include mine depth, mining method, overburden composition, and agency regulations. Mining engineers, therefore, have to balance three objectives: safety, engineering, and cost. While safety is obviously paramount, and engineering often complements safety, the cost effectiveness of any product, method, or device warrants additional consideration in today's harsh business climate. Avenues for adaptation and improvement are found at the intersection of the three objectives."

Jan 1, 2016

By Frank Schmidt

Due to changing geology, rib bolting is an ever-changing problem in ground control. With the economic status of the coal market, the need for safely increasing productivity in rib bolting is at an all-time high. The current solutions used in the market often require a long installation time (e.g. if collapsed holes have to be redrilled) or result in poor quality installations that can lead to insufficient ground control. A new bolting product based on the simple screw principle has been developed to bolt ribs faster and with a more repeatable, higher level of installation quality. The paper covers the product invention and development, the fastening principle and its advantages over current systems and first experiences in the market. The first underground trials have shown that the screw anchors can be installed safely and efficiently, often faster than traditional methods. The screw anchor does not suffer from conventional bolting issues such as collapsed holes due to bad ribs. The screw anchors are designed to obtain steel failure and load testing underground shows consistent fastening in all types of conditions.

Jan 1, 2013

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 Lightfoot. Nicholas, Na Liu

"Mining in multi-seam workings has been undertaken for many years in the VK Remnant pillars above and/or below current working areas have an important influence on retreat gateroad conditions at five of the remaining six deep coal mines. These interaction effects need lo be predicted ahead of mining so that longwall panels can be positioned to minimize roadway damage and to identify areas where additional support should be installed early into competent strata when and where it is most effective.Currently, three-dimensional elastic stress analysis using MAP3D is undertaken to predict local vertical and horizontal stress magnitudes during gateroad development and in front of the face on retreat. The predicted stress fields are often used as input to FLAC for roadway modelling.Using Maltby Colliery in South Yorkshire as a case study, this paper illustrates the MAP3D approach, together with its current limitations and uncertainties. Possible future improvements in the analysis method are proposed and the authors would welcome comments on these, or suggestions for alternative approaches.MODELLING OF MULTl-SEAM LAYOUT & MULTI-SEAM INTERACTIONThe remaining large coal mines in the UK arc operating at depths of 800-1, 150 m (2,625-3,773 ft). Production panels are now mined on retreat after the accompanying single entry access roadways have been completed. These gateroads are typically supported with a system of steel rock bolts and cable in the roof and steel bolts and glass re in forced polymer (G RP) dowels in the sidewalls.In addition to new panels being mined in the vicinity of old goafed districts, a significant amount of extraction has usually already taken place in coal seams above and/or below the current working areas. This means that there is also interaction between the current workings and the remnants of the old workings in other seams. As a consequence of the mining methods employed, old workings can have a complex geometry compri ing collapsed and partially collapsed excavations intersper ed with small and large pillars of unmined coal. The unmined coal pillar act as stress concentrators that carry the overburden load while the mined out excavations create stress shadows of varying degrees depending on how much collap e and reconsolidat ion has occurred. This is illustrated by a simple elastic model as shown in Figure I."

Jan 1, 2010

By David R. Hanson

Seismic tomographic imaging, based on the same principles as a medical CAT Scan (Computer-Aided-Tomography). has been used for many years in the oil industry for large-scale subsurface stratigraphic characterization. and has most recently been applied to various structure- and stress-related problems in the coal industry. New developments in signal processing have greatly enhanced the speed, resolution, and range of applications of topographic imaging in underground settings, and recent innovations in data acquisition hardware have further increased data reliability and repeatability. Whereas past structure mapping applications relied on Seismic velocity and/or attenuation tomopraphy within an enclosed seismic source gram receiver array, recent developments in "True Reflective Tomography- (TRT TM) have expanded the application of this technology considerably. For example, in-seam TRT TM seismic reflection tray now he used to image structure, and/or old workings from one general location in the mine face areas of mains and panel developments) well ahead of planned developments largely eliminating the need to probe-hole drill on regular intervals. This new reflective technology bas also been combined with traditional cross-hole seismic tomography-providing a comprehensive, powerful tool for velocity attenuation. and reflective imagine utilizing the same source/receiver array data sets (borehole-to-borehole. borehole-to-entry and entry-to-entry). These new developments in data acquisition and image processing have greatly expanded the variety of applications for tomographic site characterization allowing the mine operator considerable flexibility to cost-effectively characterize previously inaccessible areas of the property. This paper presents examples of 2-D and 3-D .seismic topographic imaging applied to (1) the location of old works in Appalachian room-and-pillar operations and (2) the identification of anomalous zones ahead of mining/tunneling developments these applications demonstrate the state-of-the-art in seismic ground imaging using velocity, attenuation. aril reflection techniques land combinations thereon, and further illustrate the flexibility of data acquisition from a variety of tinning arid tunneling settings. Recent examples are presented from projects in the United States and Europe.

Jan 1, 2000