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By William G. Pariseau, Mark K. Larson, Douglas R. Tesarik, Heather E. Lawson

"This contribution describes development and application of a user-friendly finite element program, UT3PC, to address three important problems in underground coal mine design: (1) safety of main entries, (2) barrier pillar size needed for entry protection, and (3) safety of bleeder entries during the advance of an adjacent longwall panel. While the finite element method is by far the most popular engineering design tool of the digital age, widespread use by the mining community has been impeded by the relatively high cost of and the need for lengthy specialized training in numerical methods. Implementation of UT3PC overcomes these impediments in three easy steps: First, a material properties file is prepared for the considered site. Next, mesh generation is automatic through an interactive process. A third and last step is simply execution of the program. Examples using data from several western coal mines illustrate the ease of using the application for analysis of main entries, barrier pillars, and bleeder entry safety.INTRODUCTIONRational design of safe underground entries and crosscuts, barrier pillars, and bleeder entries begins with a site-specific analysis of stress. An analysis of stress identifies the critical regions of high-stress concentration where yielding is likely and additional or more focused ground control measures are needed. This analysis also identifies regions where stress concentration is low, and risk mitigation is less urgent. Displacements induced by mining, including roof sag, floor heave, and pillar squeeze, are also of importance to stability. The popular finite element method is well-suited for such analysis and has been in use for studying coal mine engineering problems since the late 1960s (Dahl, 1969). The method has been taught in undergraduate engineering curricula for many years and offers an alternative to existing design procedures based mostly on rules of thumb, empirical methods based on mine data, and predigital-age concepts of strata mechanics. However, despite the versatility of the finite element method, usage has been limited, mainly because of the cost of the software and the required training in numerical methods.The program UT3PC (Pariseau, 2017) has evolved from early two-dimensional versions in the era of mainframe computers. These early versions were still quite limited using only a few hundred elements that required overnight turnaround times. Recent versions of UT3PC are convenient and efficient desktop programs that use several million elements. With the advent of personal computers in the mid-1980s and subsequent increase in computer speed, expanded memory, and lower costs, applications for mining increased in three-way cooperative projects among industry, the former U.S. Bureau of Mines, and academia. The Spokane Research Center of the U.S. Bureau of Mines, in cooperation with the University of Utah, developed a two-dimensional desktop finite element program, UT2PC, available to the mining community in 1991. This was a short course offered at the 1991 SME Annual Meeting in Denver, CO."

Jan 1, 2017

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 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 Eric C. Poeck, Ryan Garvey, Ugur Ozbay, Kun Zhang

"A coal bump is characterized by the sudden failure of one or more pillars and an associated release of kinetic energy. Although the geologic conditions surrounding coal bumps are often similar, their occurrence and magnitude are difficult to predict. This paper presents the development of an approach to assess the potential for coal bumps in room and pillar mines through the use of energy concepts and special consideration of the interface properties between the coal and overlying rock. Back analyses were performed on the widespread collapse of a room and pillar mine with an associated 3.9 local magnitude seismic event. Pillar and mine-scale models were constructed using the distinct element method to simulate the mining stages leading up to the collapse. A variety of loading conditions, material properties, and interface properties were evaluated for their effect on unstable failure of single pillars, and the mine-scale model was used to study the evolution of failure during progressive mining. The extent of unstable failure was quantified in these models by calculating the total kinetic energy released during each mining stage. Through the parametric analysis of single pillar models, it was found that softening parameters in either the coal or the coal/ rock interface can individually facilitate unstable failure of pillars, but the combination of the two in a single model produced a much higher release of energy during failure. The results of the minescale model further illustrated the trend as the combination of softening parameters in the coal and coal/rock interface produced a series of failures that most accurately reflected the collapse event at the mine. The method of room and pillar stability analysis demonstrated in this study effectively explores the potential for large coal bumps.IntroductionThe analysis of coal pillar behavior is challenging because natural variability in geologic conditions requires estimation of material strengths and predicted loads for a given mining situation. Large width-to-height (w/h) ratio pillars and deep overburden present an additional challenge, as the failure behavior of such pillars is more complex and may involve unstable, sudden collapse. Empirical methods have improved the success of coal pillar design for a wide range of conditions, but, for deep cover and squat pillar (w/h > 10) geometries, pillar performance predictions are not as accurate (Mark, 2000). As with any empirical approach, more back analysis and the consideration of new variables may help improve understanding and accuracy of future designs."

Jan 1, 2015

By John G. Oldsen

Passive cable bolting and active cable trusses have been used in roof support for more than two years Excellent roof control has been experienced by many coal operations. This paper covers the new and innovative developments in cable support systems and their application in mines. Multiple cable bolts, tensioned cable bolts, coal rib wrapping, and other cable applications will be covered.

Jan 1, 1997

By Frank E. Chase

Sacrificial entries, roof slotting, and other tactics have been used to combat high horizontal stresses during roadway development in U.S. coal mines. In Australia, the "pillar extraction on the advance" mining method has been successfully employed as a horizontal stress control technique. The concept of advancing and relieving mine workings through pillar extraction developed from observations that some mines experience difficult ground conditions when advancing and retreating the first panel in a new reserve. However, conditions dramatically improve in subsequent panels. Apparently, the creation of a gob area stress relieves the adjacent panel workings. After much debate and close scrutiny, the first U.S. roof control plan to advance and relieve was approved in 1998, for the Sargent Hollow Mine in Wise County, VA. The major concern was that this mining practice places section personnel inby of the gob. The tentative approval permitted barrier pillar slabbing and removal of the adjacent development pillar during panel development. The intent of the plan was to provide a "stress shadow" for the advancing faces and outby workings to reduce the excessive number of roof falls. Sargent Hollow successfully extracted their first panel by pillaring on advance and retreat mining using posts. Mobile roof supports were employed to extract pillars while advancing the second panel. This paper summarizes Sargent Hollow Mine's experiences with the advance and relieve mining method.

Jan 1, 1999

By William J. Conrad, Ryan J. Molka, Erik C. Westman

"In order to study pillar and overburden response to retreat mining, a ground control program was conducted at a Central Appalachian mine. The program consisted of several monitoring methods including a seismic monitoring system, borehole pressure cells in the pillars, and time-lapse photogrammetry of the pillar ribs. Two parallel geophone arrays were installed, one on each side of the panel with the sensors mounted 3m (IO ft) into the roof. A total of fourteen geophones recorded more than 5,000 events during the panel retreat. A MIDAS datalogger was used to record pressure from borehole pressure cells (BPCs) located in two adjacent pillars that were not mined during retreat. A series of photographs were taken of the pillars that had the BPCs as the face approached so that deformation of the entire rib could be monitored using photogrammetry.Results showed that pillar stability and cave development were as expected. The BPCs showed an increase in loading when the face was 115 m (380 ft) inby and a clear onset of the forward abutment at 30 m (100 ft). The photogrammetry results displayed pillar deformation corresponding to the increased loading. The microseismic monitoring results showed the overburden caving inby the face, again as expected. The significance of these results lies in two points, I) we can quantify the safe manner in which this mine is conducting retreating operations, and 2) we can use volumetric technologies (photogrammetry and microseismic) to monitor entire volumes of the mine in addition to the traditional point-location geotechnical measurements (BPCs).INTRODUCTION AND BACKGROUNDExcavation of underground openings is a difficult job in a challenging environment. The rigor of the process is compounded by the lack of a method that allows quantification of changes within the rock mass as excavation progresses. Statistics kept by the Department of Labor, Mine Safety and Health Administration show that 16% of fatalities and lost time incidents in the underground mining industry are due to unexpected rock mass failure (MSHA, 2015). A recent example is the Crandall Canyon, Utah, coal mine accident caused by the vertical collapse of a longwall coal mine on August 6, 2007 (Dreger, Ford, Walter, 2008)."

Jan 1, 2016

By X. L. Yao

This paper analyses the effects of mining extraction geometry (width/depth ratio) and dip of seam on subsidence parameters based on a large Database, containing 120 longwall mining cases all within the UK coalfields. The subsidence parameters evaluated in this paper include the following: the maximum subsidence value with different goaf-treatments, the position of maximum subsidence, the position of half-subsidence, subsidence value over the rib-side, positions of maximum tensile strains, positions of inflection points and the magnitude of maximum tensile strains on both rise and dip sides. Additionally, the maximum compressive strain and two limit angles are also studied in this paper. Based on a comprehensive Database analysis, several equations are derived relating these parameters to the width/depth ratio and the dip of seam. The results should assist engineers to design new structures, or take measures to protect existing structures from strain effects. The findings of the research assist in extension of the SEH to inclined seams with greater certainty.

Jan 1, 1990

By S. MacGregor

The role of horizontal stress, its orientation and magnitude, in defining the behaviour of strata in underground coal mines has been well established. Poor panel layouts have led to gate end stress concentrations, roof falls and lost production. The ability to define the horizontal stress regime over a mine site has historically been limited to point measurements, in part due to technology and cost. Recent advances in the application of geophysical tools, notably the acoustic scanner (borehole televiewer) have resulted in a new technique to conduct stress measurements. By quantifying the nature of borehole breakout and the mechanical properties of rocks in which they occur, this technique provides the ability to: obtain a vastly greater number of measurements, both at different depths and spatial distribution, than other techniques such as overcoring or hydraulic fracturing readily obtain depth versus stress relationships define geotechnical domains on the basis of stress direction and in-situ stress magnitude for mine planning purposes This paper presents an overview of the technique and presents case histories in its application at a mine site in the Sydney Basin, Australia.

Jan 1, 2002

By Russell C. Frith

This paper examines the design of longwall shields, focusing on those aspects that are critical to either their successful application or contribution to failure during longwall extraction. In many instances, longwall shields are assessed and designed along lines similar to that of roadway ground support systems, namely according to typical or normal geotechnical conditions. However it will be contended that for longwall shields, this is inappropriate because unlike roadway ground support systems, longwall shields cannot be supplemented with additional or secondary support in localised areas of adverse geotechnical conditions. In other words, the longwall shield needs to be designed according to what are judged to be worst case or adverse geotechnical conditions?the outcome being that a well-designed shield will be significantly over-rated for the majority of its working life. Therefore, it will be argued that the additional capital cost of such shield design can be readily justified as a prudent riskbased outcome that is essential to minimising future business risks due to strata instability on the longwall face. Shield geometry will be discussed, including such relevant factors as leg angle, inclination of the top caving shield, canopy ratio, operating height range, and tip to face distance. These are all well-established longwall shield design considerations and, most importantly, areas whereby inadequate design can render a longwall shield as highly ineffective. The issue of tip to face distance will be considered in detail, in particular, the extent by which it is an important geotechnical design consideration, the conclusion being reached that, in fact, it is not. The critical importance of maximising set to yield ratio within practical operating limits will be justified, the wisdom of this having been subject to questioning in more recent technical literature. Overall, the aim is to provide the industry with a set of suggested guidelines for future use when designing longwall shields and, hopefully, to initiate discussion on a subject that, unlike roadway ground support design, is not well covered in its entirety in the published technical literature.

Jan 1, 2013

By Pierre-Yves Declercq, Andre Vervoort

"After the mass closures of entire coal mine districts in Europe at the end of the last century, a new phenomenon of surface movement was observed—an upward movement. Although most surface movement (i.e., subsidence) occurs in the months and years after mining by the longwall method, surface movement still occurs many decades after mining is terminated. After the closure and flooding of underground excavations and surrounding rock, this movement is reversed. This paper focuses on quantifying the upward movement in two neighboring coal mines (Winterslag and Zwartberg, Belgium). The study is based on data from a remote sensing technique: interferometry with synthetic aperture radar (INSAR). The results of the study show that the rate of upward movement in the decade after closure is about 10 mm/year on average. The upward movements are not linked directly to the past exploitation directly underneath a location. The amounts of subsidence at specific locations are linked mainly to their positions relative to an inverse trough shape situated over the entire mined-out areas and their immediate surroundings. Local features, such as geological faults, can have a secondary effect on the local variation of the uplift. The processes of subsidence and uplift are based on completely different mechanisms. Subsidence is initiated by a caving process, while the process of uplift is clearly linked to flooding. INTRODUCTION After the mass closures of entire coal mine districts in Europe at the end of the last century, a new phenomenon of surface movement was observed—upward movement in the area above the past exploitation and in the immediate surroundings. Of course, most surface movement (i.e., subsidence) occurs in the months and years after mining by the longwall method (Peng, 1986). This downward movement continues to occur at a smaller rate many decades after mining has been terminated when the water in the underground excavations is pumped to the surface. This is the case as long as a mine is in operation. However, after the closure and flooding of the underground excavations and the surrounding rock, this movement is reversed, and the surface is uplifted. A total uplift of about half a meter has been recorded to date. This phenomenon has been described in several different coal basins in Europe, for example, in Belgium (Devleeschouwer et al., 2008), France (Samsonov, d’Oreye, and Smets, 2013), Germany (Baglikow, 2011), the Netherlands (Caro Cuenca, Hooper, and Hanssen, 2013), and Poland (Preusse, Kateloe, and Sroka, 2013). To date, research has focused mainly on understanding the phenomenon (e.g., Herrero et al., 2012) and identifying general trends, whereby the link with the rise in water levels is an important issue (Caro Cuenca, Hooper, and Hanssen, 2013). The most accepted explanation is linked to the swelling of clay minerals in the argillaceous rocks in the coal strata (Herrero et al., 2012). Without doubt, the full explanation is complex, and swelling is probably not the only cause of the residual movement. Most coal strata rock is weakened upon contact with water. The increase in water pressure also results in a decrease in the effective stress. Both aspects facilitate the fracturing of rock, which normally would result in further subsidence. However, decreases in the effective stresses also result in the relaxation or expansion of the rock, which induces an upward movement (Fjar et al., 2008). All of these aspects, including the long-term residual subsidence due to compaction under dry conditions, result in a net upward movement. The phenomenon discussed here is clearly different from the upsidence, sometimes observed on other continents (e.g., in Australia, Galvin, 2016). When upsidence occurs, the rock near the surface bends and buckles upwards due to the overstressing of the floors of the valleys."

Jan 1, 2017

By Ihsan Berk Tulu

The complex interaction between multiple seam pillar extraction panels and variable topography can generate unexpected ground control problems. This case study describes stress-related damage in multiple seam workings that resulted in difficult operating conditions and compromised the safety of the support crews. The damage appeared to be caused by horizontal stress but the unexpected location of the damage baffled the authors. A 2D Finite element analysis was conducted of the mine layout and surface topography in an attempt to explain the observed failure. It was discovered that the topography resulted in the rotation of the major stress at the location of the current workings. The stress rotation caused asymmetrical interactions between the workings on the different coal beds, which can explain the unexpected response observed in the mine. Consequently the layout of the next panel was changed by locating the vulnerable entry 30 ft away from its originally planned position. The new location was selected to locate the entry in favorable stress conditions. The change in layout resulted in a significant improvement in conditions when the next panel was mined. At the time of writing this paper, a full panel has been developed using the modified layout without undue ground control problems. The case study demonstrates that numerical models can help engineers to interpret and solve complex multi-seam interaction problems.

Jan 1, 2014

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 Mark K. Larson, Douglas R. Tesarik, Heather E. Lawson

"Load transfer distance (LTD) is simple in concept and usually evident in underground coal mines. Many people in the mining industry recognize LTD as the distance from the panel to where the mine ribs and pillars show evidence of renewed spalling, floor heave, or other effects of increased weight due to longwall mining or pillaring. Barrier pillars, in particular, are designed to shield mains and other relatively permanent facilities from this loading. LTD is also important in determining the extent and degree to which mining increases the load on pillars and ribs in the gate roads. Generally, a long LTD reduces loads in gate roads, but may require larger barrier pillar widths to protect mains or adjacent panels from excessive loads. Therefore, a long LTD may make it easy or difficult to meet various objectives of mine layout design . LTD reflects overburden geology in two ways: First, overburden that is weak and readily caves will limit both the amount and distance of load transfer. Second, stronger, stiffer, sandier, and more massive overburden increases both the amount and distance of load transfer. As such, LTD is central to coal mine layout design and calibration of numerical models that seek to anticipate these transfers of load during mining. However, the term does not have a consistent definition in the literature, and various instruments and observational techniques with varying sensitivities and thresholds have been used to indicate the onset of mining-induced stress increase and, subsequently, to determine an LTD. Consistency is important for meaningful comparison of ground response between mining sites and for accurate calibration of models.This paper adds to the body of observed and reported LTDs by presenting cases with relatively sandy and massive overburden at two western coal mines. These two cases include observation and measurement of LTD with multiple methods and provide insight into how distances reported relative to different criteria and instrumentation could be adjusted for comparison against a common base. This base is the criteria used by Peng and Chiang (1984) to determine their empirical equation. In one of these two cases, LTD was recently measured at a western U.S. coal mine (Mine A) to be approximately four times that calculated using the Peng and Chiang empirical equation. LTD measurements were examined using various instruments at Mine A and at adjacent Mine B. The measurements at Mine B showed that LTD was significantly greater than that calculated by the Peng and Chiang equation. Difficulties with BPC installation and fittings at Mine B permitted only ranges of LTD to be determined from some BPCs. Even so, the LTDs and ranges of LTDs determined were consistent with the LTDs determined at Mine A."

Jan 1, 2015

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 Zach G. Agioutantis

The Illinois Basin has an extensive history with the use of mechanized longwall mining dating back to the early 1970?s. In recent times, technological advances have resulted in increased panel widths from 800 feet to over 1400 feet and daily panel advance rates have also increased significant l. The prediction and control of subsidence and surface deformation due to underground mining are important considerations in the permitting, planning, and monitoring of these coal mining operations. The prediction of mining-induced ground movements using the influence function method is a mature technology, well utilized in the Illinois basin, and widely used by researchers and planning engineers around the world. This paper utilizes subsidence data, recently measured in longwall operations in Illinois, to develop an updated ground movement prediction capability implemented by the Surface Deformation Prediction System (SDPS) software package.

Jan 1, 2014

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 William G. Pariseau, Michael K. McCarter

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

Jan 1, 2016

By Zbigniew Lubosik, Stanislaw Prusek

"The main elements of hard coal extraction systems in the Polish mining industry, including the characteristics of gateroads, are described, followed by several dozen underground measurements of gateroad roof sag performed in different geological and mining conditions in Upper Silesia Coal Basin.Based on the analysis of the roof sag measurements, an attempt to describe the gateroad roof sag process using a geometrical model was made. To build the model, it was assumed that the roof sag curve could be described by three straight lines. The first line describes the roof sag ahead of the longwall face; the second line, the sag at the longwall-gateroad junction zone; and the last line describes the zone behind the longwall face. Determining the intersection points and inclination angles is essential for the model. These model parameters depend on the geological and mining conditions in the gateroad.Using the statistical computations and analysis, the dependencies between the characteristic points of the gateroad roof sag model and the selected geological and mining parameters were defined. The STATISTICA computer program by StatSoft was used for computation.This paper presents a simple form of the geometrical description of roadway roof sag progression that is very useful during the gateroad support design process.INTRODUCTIONThe longwall system with caving is the dominant method in European mining in cases of hard coal seam extraction. For instance, in Poland, in 2009, 117 longwalls were driven, with total production of 77.5 million tonnes. In roughly 95% of the longwalls, mining operations were conducted using longwalls with roof caving; the remaining 5% used the hydraulic stowing system. The average mining depth was about 700 m (2,297 ft), and average daily output per face was approximately 2,600 tonnes per day. When using the longwall mining system, gateroads play an important role. These principal roadways transport materials, mine crews, and output. In addition, they impact ventilation of the extraction area, affecting, among other things, the climatic conditions or methane hazard. Unfortunately, difficulties often appear in maintaining an adequate size for the gateroads, due to the face line, which causes origination zones with stress concentration around the gateroad, resulting in rock mass movements in the form ofroofsag, floor heave, or horizontal convergence (Figure 1)."

Jan 1, 2010

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