岩石材料尺寸效应的试验和理论研究

EXPERIMENTAL AND THEORETICAL STUDY OF SIZE EFFECT OF ROCK MATERIAL

通过在伺服试验机上对同直径不同长度大理岩样进行单轴压缩试验,研究了尺寸对岩石强度和变形特性以及破裂形式的影响规律,结果表明,岩石长度对峰值应力前的变形特性没有显著影响,但明显改变峰后的变形特性,长度越大的岩样,岩石峰后越脆;且直径一定时随着长度的增大,岩样破裂形式由竖向劈裂变为剪切破坏。岩石材料强度长度效应是由于岩样端部摩擦效应所致,而并非根源于材料的非均质性。提出了大理岩石材料尺寸效应的理论模型F0=F2exp[a+b(D/L)],所得理论曲线与试验值吻合得很好,其中物理参数a反应了岩石材料力学参数对尺寸的敏感程度,而物理参数b反应了岩石材料力学参数与尺寸的相关性,b>0呈负相关,b<0呈正相关,而b=0无相关性。

Uniaxial compression tests with marble specimens of different length-to-diameter ratios were carried out on a servo-controlled testing machine. The effect of the specimen length on the unconfined strength and the failure pattern was investigated. There is no clear effect of the specimen length on the deformation before stress peal whereas there is significant effect aider stress peak. The longer the specimen length is, the more brittle the material becomes aider the stress peak. Failure of rock specimens changes from splitting pattern into shear pattern with the increase of length. The length effect results from the friction between the end faces of rock specimens and the loading platens, not the heterogeneity of rock material. A theoretical model of size effect of marble material, F0=F2exp[a＋b（D/L）], is brought forward, which is verified by experimental data. Physical parameter a reflects the sensitivity of mechanical parameters on the size; b reflects the relation between mechanical parameters and sizes, which shows negative pertinence if b〉0, positive pertinence if b〈0, and no pertinence if b=0.