国标GB/T 50266中圆柱试件高径比取值问题研究

Study on the Problem of the Ratio of Height to Diameter of Cylindrical Specimens in National Standard GB/T 50266

国标《工程岩体试验方法标准》(GB/T 50266-2013)和电力行业标准《水利水电工程岩石试验规程》(DL/T 5368-2007)中,建议对于能制成圆柱形试件的各类岩石,圆柱直径宜为48mm^54mm,高径比宜为2.0~2.5,而国际岩石力学学会(ISRM)推荐的高径比为2.5~3.0,但目前我国工程界与学术界普遍采用高径比为2的圆柱形试件,也就是高径比取了国标建议值的下限.针对这一问题,基于莫尔-库仑准则,根据常见岩石的强度参数,反算了轴向压缩时剪切破坏模式下的最危险破裂角,结果表明:对于大多数岩石,3倍高径比基本可以消除端部约束对真实强度的影响,说明ISRM的推荐值具有科学性.结合国标GB/T 50266-2013对高径比的建议值,推荐采用2.5倍高径比,既可消除端部约束对真实强度的影响,也在国标建议值范围内,同时也与ISRM推荐值接轨.

According to national standard of Standard for Test Methods of Engineering Rock Mass（GB/T 50266-2013）and power industry standard for Rock Tests of Hydro-power and Water Conservancy Engineering（DL/T 5368-2007）,it is proposed that for all kinds of rocks which can be made into cylindrical specimens,the best appropriate diameter of cylinder should be 48mm^54mm,and the ratio of height to diameter should be 2.0~2.5.Although the International Society for Rock Mechanics （ISRM） recommends a ratio of height to diameter of 2.5~3.0,the engineering and academic circles of China generally use cylindrical specimens with the diameter ratio of 2,which means the lower limit of ratio of height to diameter recommended by the national standard is adopted.Thus,based on Mohr-Coulomb criterion,according to the strength parameters of common rocks, in this study,the most dangerous rupture angle of shear failure mode under axial compression was calculated.The results indicate that for most rocks,three times on ratio of height to diameter can basically eliminate the impact of end constraint on real strength,which means that the recommended ratio of ISRM is scientific.Combined with the recommended ratio of height to diameter by national standard GB/T 50266-2013,the ratio of height to diameter 2.5 is recommended,which can eliminate the impact of end constraint on real strength,and is within the proposed scope of national standard.It is also in line with the recommended value of ISRM.