Laboratory investigation of the anisotropic confinement-dependent brittle-ductile transition of a Utah coal  

作　　者：Bo-Hyun Kim Mark K.Larson 

机构地区：[1]Mine Safety Branch,CDC/NIOSH/SMRD,Spokane,WA 99207,USA

出　　处：《International Journal of Mining Science and Technology》2021年第1期51-57,共7页矿业科学技术学报（英文版）

基　　金：The authors would like to thanks to Steve Berry at Montana Tech for his working on the lab testing.

摘　　要：This paper was developed as part of an effort by the National Institute for Occupational Safety and Health(NIOSH)to identify risk factors associated with bumps in the prevention of fatalities and accidents in highly stressed,bump-prone ground conditions.Changes of failure mechanism with increasing confinement,from extensional-to shear-dominated failure,are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses.In the previous analysis conducted in 2018,both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of some specimens of a Utah coal,including the spalling limits,the ratio of apparent unconfined compressive strength(AUCS)to unconfined compressive strength(UCS),the damage characteristics,and the postyield dilatancy.These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction.However,the transition from extensional to shear failure at the given confinements was not clearly identified.In this study,a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive conditions.The different confining stresses are used as analogs for different width-to-height(W/H)ratios of pillar strength.Although the W/H ratios of the specimens were not directly considered during testing,the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an existing empirical solution.According to this relationship,theW/H atwhich in-situ pillar behavior would be expected to transition from brittle to ductile is identified.

关 键 词：Bump-prone ground conditions A Utah coal ANISOTROPIC Equivalent W/H ratios of a pillar 

分 类 号：TD79[矿业工程—矿井通风与安全] TD311