砂岩巴西劈裂抗拉强度的尺寸效应研究

尺寸效应是岩石力学试验研究中不可回避的问题,直接关系到岩石力学参数取值是否合理。在以往岩石劈裂抗拉强度的尺寸效应研究中,主要考虑了岩样厚径比的影响,较少考虑岩样直径的影响。基于此,在前期研究的基础上,设计进行了25,30,50,100,150 mm 5种直径岩样的巴西劈裂试验。研究结果表明:①在厚径比一定的情况下,岩样直径从25 mm增大到150 mm,对应抗拉强度呈现先陡后缓的降低趋势,在岩样直径>50 mm后,抗拉强度趋于稳定,变化趋势总体可以用指数函数较好地表达;②岩石的劈裂抗拉强度尺寸效应,不仅与岩样的厚径比有关,而且与岩样的直径有关,综合以往研究经验,建议控制岩样的厚径比为0.3左右、直径在50 mm以上,这样可以较好地消除尺寸效应对劈裂抗拉强度的影响。相关研究结果可为岩石劈裂抗拉强度的尺寸效应分析提供较好的依据。

Size Effect on Brazilian Splitting Tensile Strength of Sandstone

Size effect is an unavoidable problem in rock mechanics experiment, and is directly related to the rationality of rock mechanics parameters. In previous studies on the size effect of rock splitting tensile strength, the influence of thickness-to-diameter ratio of rock specimen was mostly considered rather than the influence of rock sample diameter. In view of this, we performed Brazilian splitting tensile strength tests on specimens of five different diameters (25, 30, 50, 100, 150 mm). Results unveiled that: 1) at given thickness-to-diameter ratio, the tensile strength of rock sample declined from being sharply towards gently as the diameter augmented from 25 mm to 150 mm. When the diameter exceeded 50 mm, tensile strength tended to be stable. Such variation trend can be well fitted by exponential function. 2) The size effect of splitting tensile strength of rock is not only related to the thickness-to-diameter ratio, but also related to the diameter of rock specimen. According to previous research experience, we suggest that the thickness-to-diameter ratio around 0.3, and diameter more than 50 mm, in which case the size effect on splitting tensile strength can be well eliminated.