The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research o...The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research on the dynamic response of rock beams under sudden unloading remains limited.This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams.Bottom unloading experiments were performed on rock beams with varying thicknesses and spans.The experiments recorded surface crack development and internal damage evolution using high speed photography and acoustic emission monitoring.The results show that rock beams experience multiple stress reductions after unloading,with the largest reduction occurring in the first stage.Flexural deformation was observed,becoming more pronounced as the thickness-span ratio decreased.Greater thickness increased shear cracks and crack expansion angles,while larger spans promoted tensile cracks,arched crack formation,and notable rock spalling.Acoustic emission analysis showed that signal count and energy increased with thickness and span.Finally,discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure:when the harder strata are at the top,cracks are sharp,and shear failure is more likely;when they are at the bottom,the overall failure range expands,and cracks tend to form arches.These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining.展开更多
Longhole caving method was used to mine gently inclined thick orebody step by step in a test stope of tin mine under complex filling body. The problem that the complex filling body around the stope affects the stabili...Longhole caving method was used to mine gently inclined thick orebody step by step in a test stope of tin mine under complex filling body. The problem that the complex filling body around the stope affects the stability of roof thickness, chamber and spacer pillar in actual mining was investigated; meanwhile, the formed goaf during mining is so vulnerable that surrounding rock collapses early. Based on this point, elasticity mechanics and limit span theory were used to study separately the roof thickness and the span limit of goaf formed in mining, and then a reasonable roof thickness of 8 m and goaf span of 14 m are proposed. In addition, the stability of roof thickness, chamber and spacer pillar were investigated and analyzed by using numerical analysis method; meanwhile, the field monitoring on the displacement of caving chamber was conducted. The results show that the maximum compressive stress of surrounding rock is 20 MPa, and the maximum tensile stress is 1.2 MPa, which is less than the ultimate tensile strength of 2.4 MPa. Moreover, plastic zone has little influence on stope stability. In addition, the displacement of 11 mm is also smaller. The displacement monitoring results are consistent with the numerical results. Thus, the roof thickness and span of goaf proposed are safe.展开更多
Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the tra...Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.展开更多
Some ablation experiments of Ethylene-Propylene-Diene Monomer(EPDM)insulator were carried out in quasi-static low temperature gas environment,gas-phase environment,two-phase environment with Al2O3 grain and high conce...Some ablation experiments of Ethylene-Propylene-Diene Monomer(EPDM)insulator were carried out in quasi-static low temperature gas environment,gas-phase environment,two-phase environment with Al2O3 grain and high concentration Al2O3 grain gas environments.Their charring ablation rate,thickness,surface morphology and main ingredient of the charring layer were analyzed.The experiment results show that the main influent factors for the charring ablation rate are the gas temperature,grain concentration and state of grain impact;the main influent factors for the charring layer thickness are the gas velocity and environment pressure;and the process of SiO2 migrating in the charring layer occur commonly in different gas environments.They provide a foundation for the ablation mechanism research and modeling of EPDM insulator.展开更多
基金Project(TD20240003)supported by the Ordos Science&Technology Plan,ChinaProjects(52174096,52304110)supported by the National Natural Science Foundation of China。
文摘The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research on the dynamic response of rock beams under sudden unloading remains limited.This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams.Bottom unloading experiments were performed on rock beams with varying thicknesses and spans.The experiments recorded surface crack development and internal damage evolution using high speed photography and acoustic emission monitoring.The results show that rock beams experience multiple stress reductions after unloading,with the largest reduction occurring in the first stage.Flexural deformation was observed,becoming more pronounced as the thickness-span ratio decreased.Greater thickness increased shear cracks and crack expansion angles,while larger spans promoted tensile cracks,arched crack formation,and notable rock spalling.Acoustic emission analysis showed that signal count and energy increased with thickness and span.Finally,discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure:when the harder strata are at the top,cracks are sharp,and shear failure is more likely;when they are at the bottom,the overall failure range expands,and cracks tend to form arches.These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining.
基金Project(2012BAK09B02-05)supported by the National Science and Technology Pillar Program during the 12th Five-Year Plan PeriodProject(11KF02)supported by the Research Fund of the State Key Laboratory of Coal Resources and Mine Safety
文摘Longhole caving method was used to mine gently inclined thick orebody step by step in a test stope of tin mine under complex filling body. The problem that the complex filling body around the stope affects the stability of roof thickness, chamber and spacer pillar in actual mining was investigated; meanwhile, the formed goaf during mining is so vulnerable that surrounding rock collapses early. Based on this point, elasticity mechanics and limit span theory were used to study separately the roof thickness and the span limit of goaf formed in mining, and then a reasonable roof thickness of 8 m and goaf span of 14 m are proposed. In addition, the stability of roof thickness, chamber and spacer pillar were investigated and analyzed by using numerical analysis method; meanwhile, the field monitoring on the displacement of caving chamber was conducted. The results show that the maximum compressive stress of surrounding rock is 20 MPa, and the maximum tensile stress is 1.2 MPa, which is less than the ultimate tensile strength of 2.4 MPa. Moreover, plastic zone has little influence on stope stability. In addition, the displacement of 11 mm is also smaller. The displacement monitoring results are consistent with the numerical results. Thus, the roof thickness and span of goaf proposed are safe.
基金Project (51775479) supported by the National Natural Science Foundation of ChinaProject (E2017203046) supported by the Natural Science Foundation of Hebei Province,China
文摘Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.
基金Sponsored by the National Nature Science Foundation of China(50876091)
文摘Some ablation experiments of Ethylene-Propylene-Diene Monomer(EPDM)insulator were carried out in quasi-static low temperature gas environment,gas-phase environment,two-phase environment with Al2O3 grain and high concentration Al2O3 grain gas environments.Their charring ablation rate,thickness,surface morphology and main ingredient of the charring layer were analyzed.The experiment results show that the main influent factors for the charring ablation rate are the gas temperature,grain concentration and state of grain impact;the main influent factors for the charring layer thickness are the gas velocity and environment pressure;and the process of SiO2 migrating in the charring layer occur commonly in different gas environments.They provide a foundation for the ablation mechanism research and modeling of EPDM insulator.
