Destress blasting(DB)implemented along the perimeter of safety pillars is a special application of destressing in coal longwall mining.The goal is to separate relatively more deformed mined areas from safety pillars,s...Destress blasting(DB)implemented along the perimeter of safety pillars is a special application of destressing in coal longwall mining.The goal is to separate relatively more deformed mined areas from safety pillars,such as shaft pillars or cross-cut pillars,to reduce the transfer of high stresses to the protective pillar.This case study aims to numerically simulate selected destress blasts in the Czech part of the Upper Silesian Coal Basin and examine its impact on stress transfer to the safety pillar area.To separate the area between the protective pillar and the longwall(LW),two fans of five 93-mm blast holes(length of 93e100 m)were drilled from the gate roads into the overburden strata.Each set of blast holes was fired separately in two stages without time delay.The explosive charge(gelatin-type of explosive)of each stage is 3450 kg.The two DB stages were fired when the longwall face was approximately 158 m and 152 m away from the blast.A 3D mine-wide model is built and validated with in situ stress measured with hydrofracturing.Mining and destressing in three 5-m thick coal seams are simulated in the region.Numerical modeling of DB is successfully conducted using a rock fragmentation factor a of 0.05 and a stress reduction/dissipation factor β of 0.95.Buffering of transfer of additional stress from the mining area into the safety pillar is evaluated by comparison of yielding volume before and after DB.It is shown that yielding volume drops after DB by nearly 80%in the area of the destressing panel and near the safety shaft pillar.展开更多
The changeable structure and movement law of overlying strata are the maincontributor to the change of mining stress.Starting from the relevant theory of keystratum and particularly based on the theory of mine ground ...The changeable structure and movement law of overlying strata are the maincontributor to the change of mining stress.Starting from the relevant theory of keystratum and particularly based on the theory of mine ground pressure and strata control,this research proposed a new solution to mining stress problems by establishing adual-load-zone stratum structural model.Elastic foundation beam theory was used tosolve the stress of overlying strata of the dual-load-zones with superposition method,which revised the traditional calculation method of mining stress.The abnormal increaseof lead abutment pressure in the mining area was explained effectively,through which theevolution law of mining stress in the case of hard rock was obtained.The results indicatethat mining stress experiences a drastic change within the range of 50 m ahead of the coalwall due to the collapse of main roof;under the influence of main key stratum andinferior key strata,the influence range of lead abutment pressure is extended up toapproximately 120 m in the working face;this remarkable increase can be attributed tothe excessive length of sagging zone.Results from both the dual-load-zone modelexperiment and field measurement demonstrate high consistency.The model can predictthe influence range of abutment pressure effectively and thus guide the safety productionof mining.展开更多
A test system was designed by using a set of self-made experimental devicesof coupled coal-gas in simulating mining stress effect, combining the equipment withRMT-150B rock mechanical experimental system, monitoring t...A test system was designed by using a set of self-made experimental devicesof coupled coal-gas in simulating mining stress effect, combining the equipment withRMT-150B rock mechanical experimental system, monitoring the rupture process ofcoal-rock with an acoustic emission (AE) device and collecting gas-flow rate andgas-stress data in real-time automatically with a gas flow-meter and gas pressure sensor.The fracture process and permeability properties test of the coal-rock in mining stress effect was carried out. Test results indicate that AE events and variation of stresses have thesame variance tendency and the rupture process of coal-rock can be monitored by AE.The relation curves among stresses, parameters of AE and permeability properties demonstrate that the permeability of coal-rock decreases gradually at quasi-elastic stage, increases gradually at plastic damage micro-fracture stage, rises suddenly near the peakpoint and has multi-variation at post-peak slip stage. From the results, such conclusioncan be drawn that the variation of permeability can be monitored by AE parameters orstress change.展开更多
The breaking features and stress distribution of overlying strata in a steeply dipping coal seam(SDCS)differ significantly from those in a near-horizontal one.In this study,the laws governing the evolution of vertical...The breaking features and stress distribution of overlying strata in a steeply dipping coal seam(SDCS)differ significantly from those in a near-horizontal one.In this study,the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation,rock mechanics tests,acoustic emissions,and field measurements.Thus,the stress-driven dynamic evolution of the overlying strata structure,in which a shear stress arch forms,is determined.Upon breaking the lower pari of the overlying strata,the shear stress transfers rapidly to the upper part of the working face.The damaged zone of the overlying strata migrates upward along the dip direction of the working face.The gangue in the lower part of the working face is compacted,leading to an increase in vertical stress.As the dip angle of the coal seam increases,the overlying strata fail suddenly under the action of shear stresses.Finally,the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail.The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS,which in turn can be used to establish the respective on-site guidance.展开更多
Aiming at the difficulty in stress analysis for strata under pillars with actual bearing conditions, an approach was proposed to apply multi-sectional linear approximation to the characteristic curves of pillar loads,...Aiming at the difficulty in stress analysis for strata under pillars with actual bearing conditions, an approach was proposed to apply multi-sectional linear approximation to the characteristic curves of pillar loads, and stress of strata was calculated under pillars with linear load by calculation method for uniform load. This approach leads to a rapid analyzing method for strata stress under pillars with any form of loads. Through theoretical analysis, strata stress expressions for pillars under linear bearing conditions are obtained. In addition, two concepts, stress increase factor and stress factor, are proposed for the approximate analysis of strata stress by uniform load approximation method. It is also found that the stress increase factor of strata is related to the strata stress factor and the ratio of the minimum load on the pillar' two ends to the maximum one; and the distribution features of stress factors and the sizes of their influencing areas in strata influenced by overlying pillars are obtained. Combining with the gob pillar conditions of Jurassic coal seam in Tongxin Coal Mine, it is demonstrated that the results obtained by stress distribution analysis of the strata stress in non-influencing areas of pillars with linear bearing through uniform load approximation are in basic accordance with the results obtained for pillars under linear bearing condition. Therefore, it is feasible and accurate to calculate stress in non-influencing area in strata under pillars with linear bearing condition by uniform load calculation method.展开更多
Through the analysis of the occurring and developing process of the rockburst under the high strata stress, it points out that the action of stress wave is the key factor to affect the rockburst process. The character...Through the analysis of the occurring and developing process of the rockburst under the high strata stress, it points out that the action of stress wave is the key factor to affect the rockburst process. The characteristics of stress wave as well as its relation with the strata stress and the mechanism of its causing rockburst are explained. Finally, the preventing measures of the rockburst caused by the stress wave are put forward.展开更多
文摘Destress blasting(DB)implemented along the perimeter of safety pillars is a special application of destressing in coal longwall mining.The goal is to separate relatively more deformed mined areas from safety pillars,such as shaft pillars or cross-cut pillars,to reduce the transfer of high stresses to the protective pillar.This case study aims to numerically simulate selected destress blasts in the Czech part of the Upper Silesian Coal Basin and examine its impact on stress transfer to the safety pillar area.To separate the area between the protective pillar and the longwall(LW),two fans of five 93-mm blast holes(length of 93e100 m)were drilled from the gate roads into the overburden strata.Each set of blast holes was fired separately in two stages without time delay.The explosive charge(gelatin-type of explosive)of each stage is 3450 kg.The two DB stages were fired when the longwall face was approximately 158 m and 152 m away from the blast.A 3D mine-wide model is built and validated with in situ stress measured with hydrofracturing.Mining and destressing in three 5-m thick coal seams are simulated in the region.Numerical modeling of DB is successfully conducted using a rock fragmentation factor a of 0.05 and a stress reduction/dissipation factor β of 0.95.Buffering of transfer of additional stress from the mining area into the safety pillar is evaluated by comparison of yielding volume before and after DB.It is shown that yielding volume drops after DB by nearly 80%in the area of the destressing panel and near the safety shaft pillar.
基金This research is supported by the National Natural Science Foundation of China(51874289)and the National Key Research and Development Program of China(2018YFC0604705)and the Fundamental Research Funds for the Central Universities 2018ZDPY05.There is no conflict of interest regarding the publication of this paper.
文摘The changeable structure and movement law of overlying strata are the maincontributor to the change of mining stress.Starting from the relevant theory of keystratum and particularly based on the theory of mine ground pressure and strata control,this research proposed a new solution to mining stress problems by establishing adual-load-zone stratum structural model.Elastic foundation beam theory was used tosolve the stress of overlying strata of the dual-load-zones with superposition method,which revised the traditional calculation method of mining stress.The abnormal increaseof lead abutment pressure in the mining area was explained effectively,through which theevolution law of mining stress in the case of hard rock was obtained.The results indicatethat mining stress experiences a drastic change within the range of 50 m ahead of the coalwall due to the collapse of main roof;under the influence of main key stratum andinferior key strata,the influence range of lead abutment pressure is extended up toapproximately 120 m in the working face;this remarkable increase can be attributed tothe excessive length of sagging zone.Results from both the dual-load-zone modelexperiment and field measurement demonstrate high consistency.The model can predictthe influence range of abutment pressure effectively and thus guide the safety productionof mining.
基金Supported by Significant Public Welfare Project of Henan Province (08110091500)the Research Fund for the Doctoral Program of Higher Education(20070460001 )National Nature Science Foundation of China(50478061)
文摘A test system was designed by using a set of self-made experimental devicesof coupled coal-gas in simulating mining stress effect, combining the equipment withRMT-150B rock mechanical experimental system, monitoring the rupture process ofcoal-rock with an acoustic emission (AE) device and collecting gas-flow rate andgas-stress data in real-time automatically with a gas flow-meter and gas pressure sensor.The fracture process and permeability properties test of the coal-rock in mining stress effect was carried out. Test results indicate that AE events and variation of stresses have thesame variance tendency and the rupture process of coal-rock can be monitored by AE.The relation curves among stresses, parameters of AE and permeability properties demonstrate that the permeability of coal-rock decreases gradually at quasi-elastic stage, increases gradually at plastic damage micro-fracture stage, rises suddenly near the peakpoint and has multi-variation at post-peak slip stage. From the results, such conclusioncan be drawn that the variation of permeability can be monitored by AE parameters orstress change.
基金the National Natural Science Foundation of China(Grant No.51634007)the Graduate Innovation Fund Project of Anhui University of Science and Technology of China(Grant No.2019CX1003).
文摘The breaking features and stress distribution of overlying strata in a steeply dipping coal seam(SDCS)differ significantly from those in a near-horizontal one.In this study,the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation,rock mechanics tests,acoustic emissions,and field measurements.Thus,the stress-driven dynamic evolution of the overlying strata structure,in which a shear stress arch forms,is determined.Upon breaking the lower pari of the overlying strata,the shear stress transfers rapidly to the upper part of the working face.The damaged zone of the overlying strata migrates upward along the dip direction of the working face.The gangue in the lower part of the working face is compacted,leading to an increase in vertical stress.As the dip angle of the coal seam increases,the overlying strata fail suddenly under the action of shear stresses.Finally,the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail.The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS,which in turn can be used to establish the respective on-site guidance.
基金Project(51174192) supported by the National Natural Science Foundation of ChinaProject(BRA2010024) supported by"333"Training Foundation of Jiangsu Province,ChinaProject(CXLX12_0964) supported by Innovation Project of Graduate Students Training of Jiangsu Province,China
文摘Aiming at the difficulty in stress analysis for strata under pillars with actual bearing conditions, an approach was proposed to apply multi-sectional linear approximation to the characteristic curves of pillar loads, and stress of strata was calculated under pillars with linear load by calculation method for uniform load. This approach leads to a rapid analyzing method for strata stress under pillars with any form of loads. Through theoretical analysis, strata stress expressions for pillars under linear bearing conditions are obtained. In addition, two concepts, stress increase factor and stress factor, are proposed for the approximate analysis of strata stress by uniform load approximation method. It is also found that the stress increase factor of strata is related to the strata stress factor and the ratio of the minimum load on the pillar' two ends to the maximum one; and the distribution features of stress factors and the sizes of their influencing areas in strata influenced by overlying pillars are obtained. Combining with the gob pillar conditions of Jurassic coal seam in Tongxin Coal Mine, it is demonstrated that the results obtained by stress distribution analysis of the strata stress in non-influencing areas of pillars with linear bearing through uniform load approximation are in basic accordance with the results obtained for pillars under linear bearing condition. Therefore, it is feasible and accurate to calculate stress in non-influencing area in strata under pillars with linear bearing condition by uniform load calculation method.
文摘Through the analysis of the occurring and developing process of the rockburst under the high strata stress, it points out that the action of stress wave is the key factor to affect the rockburst process. The characteristics of stress wave as well as its relation with the strata stress and the mechanism of its causing rockburst are explained. Finally, the preventing measures of the rockburst caused by the stress wave are put forward.
