基于应力–应变曲线的岩石脆性特征定量评价方法

QUANTITATIVE EVALUATION OF ROCK BRITTLENESS BASED ON STRESS-STRAIN CURVE

脆性是岩石的一种重要性质,岩石的许多力学行为都与其脆性有关。总结现有的基于强度、应力–应变曲线、加卸载试验、硬度、矿物成分等脆性指标,并详细分析这些指标在评价岩石脆性时的局限性。为合理、准确评价岩石的脆性程度,提出一种建立在应力–应变曲线峰后应力降的相对大小和绝对速率基础上、能够考虑岩石塑性屈服特性和应力状态影响的新的脆性指标,并开展单轴和三轴压缩实验对新指标进行检验。试验结果表明:水泥砂浆和大理岩脆性程度均随围压增大而减小,相同应力状态下大理岩脆性程度均大于水泥砂浆,这与二者实际脆性程度相符;单轴试验条件下灰岩、大理岩、花岗岩和红砂岩的脆性程度依次减小,破坏时的轴向应变逐渐增大,这与"应变越低脆性程度越大"吻合。试验结果可很好地验证该脆性指标的可靠性,研究成果对丰富和改进现有的岩石脆性特征评价方法具有重要意义。

Brittleness is one of the most important properties for rock materials, to which many mechanical behaviors of rock are related. Existing indices of brittleness based on strength, stress-strain curve, loading and unloading tests, hardness and mineral composition were summarized, and merits and weakness of the indices were analyzed in detail. In order to evaluate the brittleness of rocks reasonably and accurately, a new index of brittleness reflecting the characteristic of plastic yielding and the effect of stress state was introduced on basis of the relative magnitude and the absolute velocity of post peak stress dropping. Axial and triaxial compression tests were conducted to examine the new index. The results of tests show that brittleness of cement mortar and marble both decrease with the increasing of confining pressure and the brittleness of marble is greater than the one of cement mortar under the same stress state, which agree with the actual brittleness of the two rock materials. Brittleness of limestone, marble, granite and red sandstone decrease in order and their axial strain at failure increase in order gradually, which conforms to that the low values of elongation means more brittle. The test results verified the reliability of the new index of brittleness nicely which may enrich and improve the existing evaluation methods of rock brittleness.