Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dyna...Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.展开更多
Horizontal section top-coal(HSTCC)caving offers a powerful method to efficiently excavate rude coal in steep and thick seams,and pre-blasting weakening has a profound effect on pursuing great production,high efficienc...Horizontal section top-coal(HSTCC)caving offers a powerful method to efficiently excavate rude coal in steep and thick seams,and pre-blasting weakening has a profound effect on pursuing great production,high efficiency and good benefit under particular conditions like a small-scale working face with large-scale sectional caving height.+564-level HSTCC working face in B3–6coal seams of Jiangou Colliery in Urumqi was taken as study case for in situ industrial experiment.Total thickness of seams in the study case is about 50.0 m and average angel here is over 83°.In the industrial experiments,at first we adopted continuous charge machine and emulsion matrix explosive to substitute for traditional blasting schemes for specific geological settings in the study case.Hybrid analyses and assessments with blasting crack propagation analysis,abutment pressure monitoring prediction and economical benefit assessment were attributed to be able to attest pre-blasting weakening effects practically.Meanwhile crack propagation analysis after pre-blasting weakening showed that in all triple monitoring bore holes rock masses of top-coal would be fallen into three stages from the bottom up:fracture zone,plastic zone and elastic zone generally,and fracture toughness respectively in correspondent zones was calculated by the analytical formula:0.5616–0.8806,0.6403–0.9541 and0.7535–1.1900 MPa m1/2after pre-blasting weakening.Pressure monitoring prediction and economical benefit assessment also indicated that it was necessary to introduce the pre-blasting weakening with predominant blasting scheme from both views.For excavation in extremely steep and thick coal seams,relevant results would be a useful tool to study the mechanism of pre-blasting weakening both qualitatively and quantitatively.展开更多
For mining extra-steep-thick coal seam, the sublevel top coal caving is a high efficient method in practical engineering. However, major challenges associated with mining high-section top-coal-caving （HSTCC） are rel...For mining extra-steep-thick coal seam, the sublevel top coal caving is a high efficient method in practical engineering. However, major challenges associated with mining high-section top-coal-caving （HSTCC） are related to the resulting high ground stresses. Inevitability, using the high-section sublevel top coal caving for extra-steep-thick coal seam, the large scale of mined-out area appears. If the prefracture blasting and hydraulic fracture techniques are utilized, the top coal damage and cracks will develop, and the mining complexity will increase, such as seam inclination, continuity, mechanical characteristics of roof and susceptibility of top coal, etc. First, the field conditions of B1＋2 seam were investigated at the ＋588 level of the Weihuliang Underground Mine of China. Subsequently, according to caving mechanism of strata response obtained from several special models including physical simulation tests and numerical simulation models, the prefracture process including blasting and injecting water were analyzed. Then, the prefracture blasting technique was successfully applied to the caving of 52 m-sublevel seam. Finally, the effects were verified by advanced detecting instruments, and the results show these methods and measurements are feasible and valid.展开更多
基金financially supported by the Key National Basic Research Program of China (Nos.2014CB260404 and 2015CB251602)the Key National Natural Science Foundation of China (No.U13612030)+1 种基金Shaanxi Innovation Team Program (No.2013KCT-16)the High Technology Development Program of Xin Jiang Municipality (No.201432102)
文摘Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.
基金provided by the National Natural Science Foundation of China (No.11002021)the Doctoral Subject,Foundation of the Ministry of Education of China (No.20070008012)+1 种基金the National High Technology Research and Development Program of China (No.2008AA062104)Team Program for Key Scientific and Technological innovation,Shaanxi Province of China (No.2013KCT-16)
文摘Horizontal section top-coal(HSTCC)caving offers a powerful method to efficiently excavate rude coal in steep and thick seams,and pre-blasting weakening has a profound effect on pursuing great production,high efficiency and good benefit under particular conditions like a small-scale working face with large-scale sectional caving height.+564-level HSTCC working face in B3–6coal seams of Jiangou Colliery in Urumqi was taken as study case for in situ industrial experiment.Total thickness of seams in the study case is about 50.0 m and average angel here is over 83°.In the industrial experiments,at first we adopted continuous charge machine and emulsion matrix explosive to substitute for traditional blasting schemes for specific geological settings in the study case.Hybrid analyses and assessments with blasting crack propagation analysis,abutment pressure monitoring prediction and economical benefit assessment were attributed to be able to attest pre-blasting weakening effects practically.Meanwhile crack propagation analysis after pre-blasting weakening showed that in all triple monitoring bore holes rock masses of top-coal would be fallen into three stages from the bottom up:fracture zone,plastic zone and elastic zone generally,and fracture toughness respectively in correspondent zones was calculated by the analytical formula:0.5616–0.8806,0.6403–0.9541 and0.7535–1.1900 MPa m1/2after pre-blasting weakening.Pressure monitoring prediction and economical benefit assessment also indicated that it was necessary to introduce the pre-blasting weakening with predominant blasting scheme from both views.For excavation in extremely steep and thick coal seams,relevant results would be a useful tool to study the mechanism of pre-blasting weakening both qualitatively and quantitatively.
基金Supported by the Natural Science Foundation of China （50375026, 50375028）
文摘For mining extra-steep-thick coal seam, the sublevel top coal caving is a high efficient method in practical engineering. However, major challenges associated with mining high-section top-coal-caving （HSTCC） are related to the resulting high ground stresses. Inevitability, using the high-section sublevel top coal caving for extra-steep-thick coal seam, the large scale of mined-out area appears. If the prefracture blasting and hydraulic fracture techniques are utilized, the top coal damage and cracks will develop, and the mining complexity will increase, such as seam inclination, continuity, mechanical characteristics of roof and susceptibility of top coal, etc. First, the field conditions of B1＋2 seam were investigated at the ＋588 level of the Weihuliang Underground Mine of China. Subsequently, according to caving mechanism of strata response obtained from several special models including physical simulation tests and numerical simulation models, the prefracture process including blasting and injecting water were analyzed. Then, the prefracture blasting technique was successfully applied to the caving of 52 m-sublevel seam. Finally, the effects were verified by advanced detecting instruments, and the results show these methods and measurements are feasible and valid.
