This paper seeks to enhance the understanding that the horizontal stresses build up and release during coal pillar loading and unloading(post-failure) drawing upon three decades of observations, geomechanical monitori...This paper seeks to enhance the understanding that the horizontal stresses build up and release during coal pillar loading and unloading(post-failure) drawing upon three decades of observations, geomechanical monitoring and numerical modeling in bump-prone U.S. mines. The focus is on induced horizontal stress in mine pillars and surrounding strata as highly stressed pillars punch into the roof and floor, causing shear failure and buckling of strata; under stiff stratigraphic units of some western US mines, these events could be accompanied by violent failure of pillar cores. Pillar punching eventually results in tensile stresses at the base of the pillar, facilitating transition into the post-failure regime; this transition will be nonviolent if certain conditions are met, notably the presence of interbedded mudstones with low shear strength properties and proper mine designs for controlling seismicity and dynamic loads. The study clearly shows high confining stress build-up in coal pillars resulting in up to twice higher peak vertical stress and high strain energy accumulations in some western US mines in comparison with peak stresses predicted using common empirical pillar design methods. It is the unstable release of this strain energy that can cause significant damage resulting from pillar dilation and ground movements. These forces are much greater than the capacity of most common internal support systems, resulting in horizontal stressinduced roof falls locally, in mines under unremarkable far-field horizontal stress. Attention should be placed on pillar designs as increasing support density may prove to be ineffective. This mechanism is analyzed using field measurements and generic finite-difference stress analyses. The study confirms the higher load carrying capacity of confinement-controlled coal seams in comparison with structurally controlled coal seams. Such significant differences in confining stresses are not taken into account when estimating peak pillar strength using most common empirical techniq展开更多
以美国西部3个著名的国家公园(黄石、洛基山和大峡谷)及其缓冲区为研究对象,以空间分辨率30m的3期美国国家土地覆盖数据库(National Land Cover Databases,NLCD 1992\2001\2006)为数据源,采用森林破碎化分析模型与景观指数相结合的方法...以美国西部3个著名的国家公园(黄石、洛基山和大峡谷)及其缓冲区为研究对象,以空间分辨率30m的3期美国国家土地覆盖数据库(National Land Cover Databases,NLCD 1992\2001\2006)为数据源,采用森林破碎化分析模型与景观指数相结合的方法刻画国家公园及其缓冲区内森林破碎化及干扰模式的时空差异,并有效分离导致森林破碎化的人为干扰和自然干扰贡献份额。结果表明:美国西部国家公园内森林因严格保护而破碎化程度较低且森林状态保持稳定,主要的干扰形式是自然干扰并伴有少量的城市土地利用类型的空间交互。而在缓冲区,由于存在相对宽松的森林经营活动森林破碎化程度较高,森林受自然干扰和人为干扰共同作用,其中农业土地利用扮演主要角色。这些差异主要归因于美国西部陡峻的地形、土地所有权及民众的生活方式。为了有效改善中国森林及国家公园的管理水平,可充分借鉴美国国家公园管理过程中的先进的经营理念、法律依据、管理机制、资金机制和监督机制等,并应在森林经营实践中确保森林保护政策有效执行。展开更多
Methods of improving seismic event locations were investigated as part of a research study aimed at reducing ground control safety hazards. Seismic event waveforms collected with a 23-station three-dimensional sensor ...Methods of improving seismic event locations were investigated as part of a research study aimed at reducing ground control safety hazards. Seismic event waveforms collected with a 23-station three-dimensional sensor array during longwall coal mining provide the data set used in the analyses. A spatially variable seismic velocity model is constructed using seismic event sources in a passive tomographic method. The resulting three-dimensional velocity model is used to relocate seismic event positions. An evolutionary optimization algorithm is implemented and used in both the velocity model development and in seeking improved event location solutions. Results obtained using the different velocity models are compared. The combination of the tomographic velocity model development and evolutionary search algorithm provides improvement to the event locations.展开更多
文摘This paper seeks to enhance the understanding that the horizontal stresses build up and release during coal pillar loading and unloading(post-failure) drawing upon three decades of observations, geomechanical monitoring and numerical modeling in bump-prone U.S. mines. The focus is on induced horizontal stress in mine pillars and surrounding strata as highly stressed pillars punch into the roof and floor, causing shear failure and buckling of strata; under stiff stratigraphic units of some western US mines, these events could be accompanied by violent failure of pillar cores. Pillar punching eventually results in tensile stresses at the base of the pillar, facilitating transition into the post-failure regime; this transition will be nonviolent if certain conditions are met, notably the presence of interbedded mudstones with low shear strength properties and proper mine designs for controlling seismicity and dynamic loads. The study clearly shows high confining stress build-up in coal pillars resulting in up to twice higher peak vertical stress and high strain energy accumulations in some western US mines in comparison with peak stresses predicted using common empirical pillar design methods. It is the unstable release of this strain energy that can cause significant damage resulting from pillar dilation and ground movements. These forces are much greater than the capacity of most common internal support systems, resulting in horizontal stressinduced roof falls locally, in mines under unremarkable far-field horizontal stress. Attention should be placed on pillar designs as increasing support density may prove to be ineffective. This mechanism is analyzed using field measurements and generic finite-difference stress analyses. The study confirms the higher load carrying capacity of confinement-controlled coal seams in comparison with structurally controlled coal seams. Such significant differences in confining stresses are not taken into account when estimating peak pillar strength using most common empirical techniq
文摘以美国西部3个著名的国家公园(黄石、洛基山和大峡谷)及其缓冲区为研究对象,以空间分辨率30m的3期美国国家土地覆盖数据库(National Land Cover Databases,NLCD 1992\2001\2006)为数据源,采用森林破碎化分析模型与景观指数相结合的方法刻画国家公园及其缓冲区内森林破碎化及干扰模式的时空差异,并有效分离导致森林破碎化的人为干扰和自然干扰贡献份额。结果表明:美国西部国家公园内森林因严格保护而破碎化程度较低且森林状态保持稳定,主要的干扰形式是自然干扰并伴有少量的城市土地利用类型的空间交互。而在缓冲区,由于存在相对宽松的森林经营活动森林破碎化程度较高,森林受自然干扰和人为干扰共同作用,其中农业土地利用扮演主要角色。这些差异主要归因于美国西部陡峻的地形、土地所有权及民众的生活方式。为了有效改善中国森林及国家公园的管理水平,可充分借鉴美国国家公园管理过程中的先进的经营理念、法律依据、管理机制、资金机制和监督机制等,并应在森林经营实践中确保森林保护政策有效执行。
文摘Methods of improving seismic event locations were investigated as part of a research study aimed at reducing ground control safety hazards. Seismic event waveforms collected with a 23-station three-dimensional sensor array during longwall coal mining provide the data set used in the analyses. A spatially variable seismic velocity model is constructed using seismic event sources in a passive tomographic method. The resulting three-dimensional velocity model is used to relocate seismic event positions. An evolutionary optimization algorithm is implemented and used in both the velocity model development and in seeking improved event location solutions. Results obtained using the different velocity models are compared. The combination of the tomographic velocity model development and evolutionary search algorithm provides improvement to the event locations.
