Last data update: May 13, 2024. (Total: 46773 publications since 2009)
Records 1-17 (of 17 Records) |
Query Trace: Tulu IB[original query] |
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Assessing Longwall Gateroad Ground Response and Support Alternatives
Esterhuizen GS , Klemetti T , Sears MM , Zhang P , van Dyke M , Dougherty H , Tulu IB . Min Metall Explor 2021 38 (4) 1739-1759 Ground falls in longwall gateroad entries remain a concern in modern longwall operations. The gateroads are subject to changing horizontal and vertical ground stress induced by longwall extraction. These stress changes can result in failure of the strata around an entry leading to large deformations of the entry roof, floor, and ribs. The gateroad support systems are required to control the failed strata while maintaining safe access to the longwall face and unimpeded ventilation. This paper presents research that was conducted to better understand the stability issues in gateroad excavations and to develop procedures for evaluating support and layout alternatives for longwall gateroads. Using the results of a field-monitoring program and numerical model analysis of case histories, a conceptual model of gateroad support needs was developed. The conceptual model formed the basis for developing a set of equations that can be used to estimate likely roof sag and support loading for given roof geology and longwall-induced loading conditions. The developed equations were used to compare predicted gateroad stability to field study results, showing satisfactory agreement. The calculation procedures are used to demonstrate their application in assessing support alternatives at a case study mine. It is concluded that the developed analysis procedures provide realistic assessments of likely ground stability and can be used to evaluate alternative gateroad support systems at operating longwall mines. © 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply. |
Re-analysis of abutment angle method for moderate and deep cover retreat room and pillar mines and investigation of loading mechanics using finite volume modeling
Tuncay D , Tulu IB , Klemetti T . Rock Mech Rock Eng 2021 54 (7) 3447-3468 Mining-induced stresses in underground coal mines play a significant role in pillar and ground support design, hence in the safety of mining operations. In the US, Analysis of Longwall Pillar Stability (ALPS) and in Australia, Analysis of Longwall Tailgate Serviceability (ALTS) software are used for designing Longwall coal mine layouts; and in the US, Analysis of Retreat Mining Pillar Stability (ARMPS) software is used to design retreat room-and-pillar mine layouts. All these software determine the adequacy of the design by comparing the estimated loads to the load-bearing capacity of the pillars and they use the “abutment angle” concept and a square decay stress distribution function to calculate the magnitude and distribution of the mining-induced loads. The abutment angle concept has been successfully applied to US longwall coal mines with the use of ALPS and ALTS in Australia. ARMPS uses the same concept for retreat room and pillar coal mine design in the US. The suggested abutment angle for coal mines in the US was derived as 21° by the back analysis of underground stress measurements from the 1990s and implemented in ALPS and ARMPS. The ALPS methodology was re-examined and calibrated for Australian conditions with additional Australian stress measurements and resulted in the original ALTS methodology which has been continually improved and expanded with additional cases. In this paper, some recent stress measurements are back-analyzed, and the abutment angles are investigated to verify the applicability of using 21° in retreat room and pillar mines with different depths and mining dimensions. For shallow mines, the derivation of the 21° abutment angle is supported by the new case histories. However, at depths greater than 200 m, the abutment angle was found to be decreasing with increasing depth. In this study, a new equation for the calculation of abutment angle for moderate and deep cover cases was constructed and tested for its applicability in retreat room and pillar mines. The differences in the mechanism of complete side abutment loads in shallow and deep cover mines are further analyzed by applying the finite volume modeling (FVM) approach to two case study mines, one shallow, and one deep cover. A 2D model of each mine is created and one-side and two-side abutment loads of consecutive panels are analyzed. Analysis of the deep cover mine indicated that the prior panel gobs provide a considerable amount of support to the overburden strata. These higher gob loads prevent a higher percentage of overburden loads from being transferred to the active panel workings, and this is in agreement with the lower abutment angles observed for deep cover mines. The findings of this study should only be used for retreat room-and-pillar mines’ production pillar loads since these are calculated geometrically using the abutment angle concept. |
Moderate cover bleeder entry and standing support performance in a longwall mine: A case study
Van Dyke MA , Klemetti TM , Tulu IB , Tuncay D . Min Metall Explor 2021 38 (2) 885-896 Bleeder entries are critically important to longwall mining for the moving of supplies, personnel, and the dilution of mine air contaminants. By design, these entries must stay open for many years for ventilation. Standing supports in moderate cover bleeder entries were observed, numerically modeled, and instrumented by researchers at the National Institute for Occupational Safety and Health (NIOSH). The measurements of the installed borehole pressure cells (BPCs), standing support load cells and convergence meters, and roof extensometers are presented in this paper in addition to the numerical modeling results and visual observations made by the NIOSH researchers in the bleeder entries. The results include the effects of multiple panels being extracted in close proximity to the instrumented site as well as over one and a half years of aging. As expected, standing supports closer to the longwall gob showed the greatest load and convergence. The roof sag appeared generally independent of the proximity to the longwall gob. The BPC readings were driven by both the proximity to the gob and the depth into the pillar. The results of this study demonstrated that the entry roof can respond independently of the pillar and standing support loading. In addition, the rear abutment stress experienced by this bleeder entry design was minimal. The closer the mine development, pillar, or supports are to the gob, the greater the applied load due to rear abutment stress. |
Application of the coal mine floor rating (CMFR) to assess the floor stability in a Central Appalachian Coal Mine
Cicek S , Tulu IB , Van Dyke M , Klemetti T , Wickline J . Int J Min Sci Technol 2020 31 (1) 83-89 Estimating the overall floor stability in a coal mine using deterministic methods which require complex engineering properties of floor strata is desirable, but generally it is impractical due to the difficulty of gathering essential input data. However, applying a quantitative methodology to describe floor quality with a single number provides a practical estimate for preliminary assessment of floor stability. The coal mine floor rating (CMFR) system, developed by the University of New South Wales (UNSW), is a rock- mass classification system that provides an indicator for the competence of floor strata. The most significant components of the CMFR are uniaxial compressive strength and discontinuity intensity of floor strata. In addition to the competence of the floor, depth of cover and stress notch angle are input parameters used to assess the preliminary floor stability. In this study, CMFR methodology was applied to a Central Appalachian Coal Mine that intermittently experienced floor heave. Exploratory drill core data, overburden maps, and mine plans were utilized for the study. Additionally, qualitative data (failure/non-failure) on floor conditions of the mine entries near the core holes was collected and analyzed so that the floor quality and its relation to entry stability could be estimated by statistical methods. It was found that the current CMFR classification system is not directly applicable in assessing the floor stability of the Central Appalachian Coal Mine. In order to extend the applicability of the CMFR classification system, the methodology was modified. A calculation procedure of one of the CMFR classification system's components, the horizontal stress rating (HSR), was changed and new parameters were added to the HSR. |
Assessing support alternatives for longwall gateroads subject to changing stress
Esterhuizen GS , Tulu IB , Gearhart DF , Dougherty H , van Dyke M . Int J Min Sci Technol 2020 31 (1) 103-110 Longwall gateroad entries are subject to changing horizontal and vertical stress induced by redistribution of loads around the extracted panel. The stress changes can result in significant deformation of the entries that may include roof sag, rib dilation, and floor heave. Mine operators install different types of supports to control the ground response and maintain safe access and ventilation of the longwall face. This paper describes recent research aimed at quantifying the effect of longwall-induced stress changes on ground stability and using the information to assess support alternatives. The research included monitoring of ground and support interaction at several operating longwall mines in the U.S., analysis and calibration of numerical models that adequately represent the bedded rock mass, and observation of the support systems and their response to changes in stress. The models were then used to investigate the impact of geology and stress conditions on ground deformation and support response for various depths of cover and geologic scenarios. The research results were summarized in two regression equations that can be used to estimate the likely roof deformation and height of roof yield due to longwall-induced stress changes. This information is then used to assess the ability of support systems to maintain the stability of the roof. The application of the method is demonstrated with a retrospective analysis of the support performance at an operating longwall mine that experienced a headgate roof fall. The method is shown to produce realistic estimates of gateroad entry stability and support performance, allowing alternative support systems to be assessed during the design and planning stage of longwall operations. |
Investigating different methods used for approximating pillar loads in longwall coal mines
Tuncay D , Tulu IB , Klemetti T . Int J Min Sci Technol 2020 31 (1) 23-32 Accurately estimating load distributions and ground responses around underground openings play a significant role in the safety of the operations in underground mines. Adequately designing pillars and other support measures relies highly on the accurate assessment of the loads that will be carried by them, as well as the load-bearing capacities of the supports. There are various methods that can be used to approximate mining-induced loads in stratified rock masses to be used in pillar design. The empirical methods are based on equations derived from large databases of various case studies. They are implemented in government approved design tools and are widely used. There are also analytical and numerical techniques used for more detailed analysis of the induced loads. In this study, two different longwall mines with different panel width-to-depth ratios are analyzed using different methods. The empirical method used in the analysis is the square-decay stress function that uses the abutment angle concept, implemented in pillar design software developed by the National Institute for Occupational Safety and Health (NIOSH). The first numerical method used in the analysis is a displacement-discontinuity (DD) variation of the boundary element method, LaModel, which utilizes the laminated overburden model. The second numerical method used in the analysis is Fast Lagrangian Analysis of Continua (FLAC) with the numerical modeling approach recently developed at West Virginia University which is based on the approach developed by NIOSH. The model includes the 2D slice of a cross-section along the width of the panel with the chain pillar system that also includes the different stratigraphic layers of the overburden. All three methods gave similar results for the shallow mine, both in terms of load percentages and distribution where the variation was more obvious for the deep cover mine. The FLAC3D model was observed to better capture the stress changes observed during the field measurements for both the shallow and deep cover cases. This study allowed us to see the shortcomings of each of these different methods. It was concluded that a numerical model which incorporates the site-specific geology would provide the most precise estimate for complex loading conditions. |
Insights into the relationships among the roof, rib, floor, and pillars of underground coal mines
Klemetti TM , Van Dyke MA , Evanek N , Compton CC , Tulu IB . Min Metall Explor 2020 38 (1) 531-538 Ground control failures continue to be one of the leading causes of injuries and fatalities in underground coal mining. The roof, rib, floor, and pillars are four areas of potential ground failures that miners, engineers, and consultants are continually evaluating. Quite often, these four underground structures are evaluated independently. A recent push to consider them as a system and in a similar manner as design engineers evaluate mechanical systems has highlighted the need to fully understand the interrelationship among the roof, rib, floor, and pillar. This relationship combines the geometry of the mine layout, geological environment, installed support, and even the timing of the coal extraction. Several studies using field observations and instrumentation show that these relationships can be independent at times, while being dependent in other scenarios. Cases with good roof conditions while the rib and floor deteriorate are contrasted with cases where the roof, rib, and floor deteriorate at the same time. The presented cases in this study demonstrate the importance of understanding the geological environment and mine design to ensure that the proper support is installed. |
Verification of 3D numerical modeling approach for longwall mines with a case study mine from the northern Appalachian coal fields
Tuncay D , Tulu IB , Klemetti T . Min Metall Explor 2020 38 (1) 447-456 Accurately estimating load distributions and ground responses around underground openings plays a significant role in the safety of the operations in underground mines. Adequately designing pillars and other support measures relies highly on the accurate assessment of the mining-induced loads, as well as the load-bearing capacities of the supports. There are various methods that can be used to approximate mining-induced loads in stratified rock masses, both empirical and numerical. In this study, the numerical modeling approach recently developed at West Virginia University, which is based on the modeling approach developed by the National Institute for Occupational Safety and Health (NIOSH), is investigated using the finite difference software FLAC3D. The model includes the longwall panels, the adjacent chain pillar systems, and the different stratigraphic layers of the overburden. Using the 3D model, changes in loading conditions and deformations on the areas of interest, induced by an approaching longwall face, can be examined. This paper details the 3D modeling of a longwall panel utilizing this approach, and the verification of the results against field observations. The studied panel was 360 m wide with a 3-entry chain pillar system and about a 160-m average overburden depth around the studied area. The overburden strata consist of alternating layers of shale, sandstone, and limestone. The FLAC3D results were compared against field measurements from the mine site. The stress change values measured in the chain pillars were comparable with the modeling results. The model also replicated the surface subsidence profile obtained from field measurements fairly well. Overall, the 3D modeling approach was found to be successful for the case study longwall panel. |
A case study of the stability of a non-typical bleeder entry system at a U.S. longwall mine
Klemetti TM , Van Dyke MA , Tulu IB , Tuncay D . Int J Min Sci Technol 2020 30 (1) 25-31 Longwall abutment loads are influenced by several factors, including depth of cover, pillar sizes, panel dimensions, geological setting, mining height, proximity to gob, intersection type, and size of the gob. How does proximity to the gob affect pillar loading and entry condition? Does the gob influence depend on whether the abutment load is a forward, side, or rear loading? Do non-typical bleeder entry systems follow the traditional front and side abutment loading and extent concepts? If not, will an improved understanding of the combined abutment extent warrant a change in pillar design or standing support in bleeder entries? This paper details observations made in the non-typical bleeder entries of a moderate depth longwall panel—specifically, data collected from borehole pressure cells and roof extensometers, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading experienced due to the extraction of the longwall panels. Due to the layout of the longwall panels and bleeder entries, the borehole pressure cells (BPCs) and roof extensometers did not show much change due to the advancing of the first longwall. However, they did show a noticeable increase due to the second longwall advancement, with a maximum of about 4 MPa of pressure increase and 5 mm of roof deformation. The observations of the conditions showed little to no change from before the first longwall panel extraction began to when the second longwall panel had been advanced more than 915 m. Localized pillar spalling was observed on the corners of the pillars closest to the longwall gob as well as an increase in water in the entries. In addition to the observations and instrumentation, numerical modeling was performed to validate modeling procedures against the monitoring results and evaluate the bleeder design. ITASCA Consulting Group's FLAC3D numerical modeling software was used to evaluate the bleeder entries. The results of the models indicated only a minor increase in load during the extraction of the longwall panels. These models showed a much greater increase in stress due to the development of the gateroad and bleeder entries–about 80% development and 20% longwall extraction. The FLAC3D model showed very good correlation between modeled and expected gateroad loading during panel extraction. The front and side abutment extent modeled was very similar to observations from this and previous panels. |
Analysis of ARMPS2010 database with LaModel and an updated abutment angle equation
Tuncay D , Tulu IB , Klemetti T . Int J Min Sci Technol 2020 30 (1) 111-118 The Analysis of Retreat Mining Pillar Stability (ARMPS) program was developed by the National Institute for Occupational Safety and Health (NIOSH) to help the United States coal mining industry to design safe retreat room-and-pillar panels. ARMPS calculates the magnitude of the in-situ and mining-induced loads by using geometrical computations and empirical rules. In particular, the program uses the “abutment angle” concept in calculating the magnitude of the abutment load on pillars adjacent to a gob. In this paper, stress measurements from United States and Australian mines with different overburden geologies with varying hard rock percentages were back analyzed. The results of the analyses indicated that for depths less than 200 m, the ARMPS empirical derivation of a 21° abutment angle was supported by the case histories; however, at depths greater than 200 m, the abutment angle was found to be significantly less than 21°. In this paper, a new equation employing the panel width to overburden depth ratio is constructed for the calculation of accurate abutment angles for deeper mining cases. The new abutment angle equation was tested using both ARMPS2010 and LaModel for the entire case history database of ARMPS2010. The new abutment angle equation to estimate the magnitude of the mining-induced loads used together with the LaModel program was found to give good classification accuracies compared to ARMPS2010 for deep cover cases. |
Overview of current US longwall gateroad support practices
Sears MM , Esterhuizen GS , Tulu IB . Min Metall Explor 2019 36 (6) 1137-1144 In 2015, 40 longwall mines provided nearly 60% of the US coal production from underground mining methods. This represents a substantial, yet gradual increase from just under 50% over the last 5 years. As a result of this increased production share, the percentage of ground fall related fatalities in longwall mines has also increased when compared to all US underground coal mines. Additionally, about 80% of ground fall related fatalities have occurred in areas where the roof was supported. In an attempt to better understand the status quo of current US longwall support practices, a sample of 21 longwall mines were visited, representing about 40% of the currently active longwall mines in 4 of the 5 major US longwall producing regions. The resulting data was obtained from a wide variety of overburden depths, geologic conditions, mining heights, ground conditions, support practices, and gateroad configurations. The data collected is reported using both qualitative and quantitative methods. The results from the research update previous efforts in classifying mining accidents and injuries as well as current support practices. This data provides a necessary background for future research aimed at further reduction of ground fall accidents and injuries. |
Analysis of monitored ground support and rock mass response in a longwall tailgate entry
Esterhuizen GS , Gearhart DF , Tulu IB . Int J Min Sci Technol 2017 28 (1) 43-51 A comprehensive monitoring program was conducted to measure the rock mass displacements, support response, and stress changes at a longwall tailgate entry in West Virginia. Monitoring was initiated a few days after development of the gateroad entries and continued during passage of the longwall panels on both sides of the entry. Monitoring included overcore stress measurements of the initial stress within the rock mass, changes in cable bolt loading, standing support pressure, roof deformation, rib deformation, stress changes in the coal pillar, and changes in the full three-dimensional stress tensor within the rock mass at six locations around the monitoring site. During the passage of the first longwall, stress measurements in the rock and coal detected minor changes in loading while minor changes were detected in roof deformation. As a result of the relatively favorable stress and geological conditions, the support systems did not experience severe loading or rock deformation until the second panel approached within 10-15 m of the instrumented locations. After reaching the peak loading at about 50-75 mm of roof sag, the cable bolts started to unload, and load was transferred to the standing supports. The standing support system was able to maintain an adequate opening inby the shields to provide ventilation to the first crosscut inby the face, as designed. The results were used to calibrate modeled cable bolt response to field data, and to validate numerical modeling procedures that have been developed to evaluate entry support systems. It is concluded that the support system was more than adequate to control the roof of the tailgate up to the longwall face location. The monitoring results have provided valuable data for the development and validation of support design strategies for longwall tailgate entries. |
Deep cover bleeder entry performance and support loading: A case study
Klemetti TM , Van Dyke MA , Tulu IB . Int J Min Sci Technol 2018 28 (1) 85-93 Several questions have emerged in relation to deep cover bleeder entry performance and support loading: how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented, observed, and numerically modeled. This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel-specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading experienced by the standing support. As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports-less than 23 Mg load and 2.54 cm convergence. The Flac3D program was used to evaluate these four bleeder entries using previously defined modeling and input parameter estimation procedures. The results indicated only a minor increase in load during the extraction of the longwall panel. The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction. The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies. The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal. The farther away from the startup room, the lower the applied load and smaller the convergence in the entry if all else is held constant. Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam. |
Analysis of global and local stress changes in a longwall gateroad
Tulu IB , Esterhuizen GS , Gearhart D , Klemetti TM , Mohamed KM , Su DWH . Int J Min Sci Technol 2017 28 (1) 127-135 A numerical-model-based approach was recently developed for estimating the changes in both the horizontal and vertical loading conditions induced by an approaching longwall face. In this approach, a systematic procedure is used to estimate the model's inputs. Shearing along the bedding planes is modeled with ubiquitous joint elements and interface elements. Coal is modeled with a newly developed coal mass model. The response of the gob is calibrated with back analysis of subsidence data and the results of previously published laboratory tests on rock fragments. The model results were verified with the subsidence and stress data recently collected from a longwall mine in the eastern United States. |
Design concerns of room and pillar retreat panels
Klemetti TM , Sears MM , Tulu IB . Int J Min Sci Technol 2016 27 (1) 29-35 Why do some room and pillar retreat panels encounter abnormal conditions? What factors deserve the most consideration during the planning and execution phases of mining and what can be done to mitigate those abnormal conditions when they are encountered? To help answer these questions, and to determine some of the relevant factors influencing the conditions of room and pillar (R & P) retreat mining entries, four consecutive R & P retreat panels were evaluated. This evaluation was intended to reinforce the influence of topographic changes, depth of cover, multiple-seam interactions, geological conditions, and mining geometry. This paper details observations were made in four consecutive R & P retreat panels and the data were collected from an instrumentation site during retreat mining. The primary focus was on the differences observed among the four panels and within the panels themselves. The instrumentation study was initially planned to evaluate the interactions between primary and secondary support, but produced rather interesting results relating to the loading encountered under the current mining conditions. In addition to the observation and instrumentation, numerical modeling was performed to evaluate the stress conditions. Both the LaModel 3.0 and Rocscience Phase 2 programs were used to evaluate these four panels. The results of both models indicated a drastic reduction in the vertical stresses experienced in these panels due to the full extraction mining in overlying seams when compared to the full overburden load. Both models showed a higher level of stress associated with the outside entries of the panels. These results agree quite well with the observations and instrumentation studies performed at the mine. These efforts provided two overarching conclusions concerning R & P retreat mine planning and execution. The first was that there are four areas that should not be overlooked during R & P retreat mining: topographic relief, multiple-seam stress relief, stress concentrations near the gob edge, and geologic changes in the immediate roof. The second is that in order to successfully retreat an R & P panel, a three-phased approach to the design and analysis of the panel should be conducted: the planning phase, evaluation phase, and monitoring phase. |
A case study of multi-seam coal mine entry stability analysis with strength reduction method
Tulu IB , Esterhuizen GS , Klemetti T , Murphy MM , Sumner J , Sloan M . Int J Min Sci Technol 2016 26 (2) 193-196 In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the Central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines. |
Analysis of alternatives for using cable bolts as primary support at two low-seam coal mines
Esterhuizen GS , Tulu IB . Int J Min Sci Technol 2015 26 (1) 23-30 Cable bolts are sometimes used in low-seam coal mines to provide support in difficult ground conditions. This paper describes cable bolting solutions at two low-seam coal mines in similar ground conditions. Both mines used support systems incorporating cable bolts as part of the primary support system. Two original cable bolt based support systems as well as two modified systems are evaluated to estimate their ability to prevent large roof falls. One of the support systems incorporated passive cable bolts, while the other used pre-tensioned cable bolts. The results and experience at the mines showed that the modified systems provided improved stability over the original support systems. The presence of the cable bolts is the most important contribution to stability against large roof falls, rather than the details of the support pattern. It was also found that a heavy steel channel can improve the safety of the system because of the 'sling' action it provides. Additionally, the analysis showed that fully-grouted rebar bolts load much earlier than the cable bolts, and pre-tensioning of the cable bolts can result in a more uniform distribution of loading in the roof. |
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