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 proximi...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 5mmof 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.展开更多
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 understan...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.展开更多
One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries.These critical entries provide much-needed safe access for miners and allow for adequate venti...One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries.These critical entries provide much-needed safe access for miners and allow for adequate ventilation required for dilution of hazardous airborne contaminants and must remain open during mining of a multi-panel district.This paper is focused on the stability of the longwall entries subjected to a single abutment load such as bleeders,first tailgate,and last headgate.First tailgate and last headgate are also referred to as blind headgate and tailgate.A study of a longwall district through conditions mapping,support evaluations,and numerical modeling was conducted and evaluated by researchers from the National Institute for Occupational Safety and Health(NIOSH).The condition mapping and support evaluations were performed on entries that spanned the previous five years of mining and relied on a diverse selection of supports to maintain the functionality of the entry.Numerical modeling was also conducted to evaluate various support types with further investigation and comparison to the condition mapping.The study demonstrated the importance of the abutment load decay versus distance from the gob edge,the potential for a reduction in material handling related injuries,as well as optimal usage of secondary and standing support.展开更多
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 pilla...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.展开更多
Caving in coal mines releases significant amounts of dust and gas. This is exhausted from the mine by forcing the air to travel through the caved zones into a set of roadways known as bleeders. These bleeder entries a...Caving in coal mines releases significant amounts of dust and gas. This is exhausted from the mine by forcing the air to travel through the caved zones into a set of roadways known as bleeders. These bleeder entries are operated for the life of the mine, and therefore, they have to be kept in stable condition. Caving operations in coal mines are associated with longwall mines and complete pillar extraction. The pillars adjoining the caved zone sometimes show rib failures, posing a hazard for mine personnel travelling through the entry. In this paper, we present the results from analyses of bleeder pillars that are near the caved zones and are susceptible to damage because of the transfer of load during the caving process.In this study, bleeder pillars were simulated in a displacement discontinuity program. Results showed that the vertical stresses on bleeder pillars increased while the safety factor of bleeder pillar decreased during the caving process; however, when the caved zone completely consolidated, both the stresses and safety factor did not change for the remaining extraction. When similar extraction was performed at deeper depths, vertical stress on pillars increased significantly.展开更多
文摘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 5mmof 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.
文摘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.
文摘One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries.These critical entries provide much-needed safe access for miners and allow for adequate ventilation required for dilution of hazardous airborne contaminants and must remain open during mining of a multi-panel district.This paper is focused on the stability of the longwall entries subjected to a single abutment load such as bleeders,first tailgate,and last headgate.First tailgate and last headgate are also referred to as blind headgate and tailgate.A study of a longwall district through conditions mapping,support evaluations,and numerical modeling was conducted and evaluated by researchers from the National Institute for Occupational Safety and Health(NIOSH).The condition mapping and support evaluations were performed on entries that spanned the previous five years of mining and relied on a diverse selection of supports to maintain the functionality of the entry.Numerical modeling was also conducted to evaluate various support types with further investigation and comparison to the condition mapping.The study demonstrated the importance of the abutment load decay versus distance from the gob edge,the potential for a reduction in material handling related injuries,as well as optimal usage of secondary and standing support.
文摘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.
基金CERB (Coal and Energy Research Bureau) for supporting this research work
文摘Caving in coal mines releases significant amounts of dust and gas. This is exhausted from the mine by forcing the air to travel through the caved zones into a set of roadways known as bleeders. These bleeder entries are operated for the life of the mine, and therefore, they have to be kept in stable condition. Caving operations in coal mines are associated with longwall mines and complete pillar extraction. The pillars adjoining the caved zone sometimes show rib failures, posing a hazard for mine personnel travelling through the entry. In this paper, we present the results from analyses of bleeder pillars that are near the caved zones and are susceptible to damage because of the transfer of load during the caving process.In this study, bleeder pillars were simulated in a displacement discontinuity program. Results showed that the vertical stresses on bleeder pillars increased while the safety factor of bleeder pillar decreased during the caving process; however, when the caved zone completely consolidated, both the stresses and safety factor did not change for the remaining extraction. When similar extraction was performed at deeper depths, vertical stress on pillars increased significantly.
