基于全应力–应变曲线及起裂应力的岩石脆性特征评价方法

脆性作为岩石重要的力学指标,准确评价岩石脆性特征对岩体工程稳定性具有重要意义。目前,常用的岩石脆性指数评价方法主要基于岩石压缩过程中峰后应力–应变曲线变化规律,而对岩石峰前应力状态关注较少。综合考量峰后应力跌落速率及起裂应力值至峰值应力值之间的应力增长速率,建立一种基于岩体应力–应变全过程的脆性指数计算方法,更加准确、合理地描述岩体脆性特征。试验结果表明:单轴条件下当全程采用轴向位移控制时,脆性较强的岩石难以准确获得其峰后曲线,容易降低基于峰后应力曲的常规脆性评价方法的准确性,而所建立的脆性指标可根据峰前曲线进行判断,能够准确评价岩石脆性程度。在三轴条件下,该脆性指标更为全面地反映了围压对大理岩脆性的抑制作用。建立的脆性指标基于岩石整个压缩过程的应力状态,能够更加显著地体现不同因素对岩石脆性特征的影响。试验结果很好地验证了该指标的准确性与优越性,研究结果对丰富与完善岩体脆性评价体系具有重要的作用。

Evaluation method of brittle characteristics of rock based on full stress-strain curve and crack initiation stress

Brittleness is an important index of rock and evaluating the brittleness accurately is of great significance in rock engineering. At present，the commonly used method to evaluate the brittleness index of rock is based on the variation of the stress strain curve in compression process，and less attention is paid to the pre-stress state. In this paper，the rate of stress drop in the post-peak state and the rate of stress increase from crack initiation to stress peak are comprehensively considered. A new method for calculating the brittleness index more accurately and reasonably based on the whole process of stress and strain of rock mass is established. It is difficult to obtain the post peak curve accurately for strong brittle rock in displacement controlled uniaxial loading tests，which affects the accuracy of the conventional method based on the post peak stress curve. The brittleness index established in this paper is according to the stress-strain curve before stress peak. Under the condition of triaxial compression，the brittle index proposed reflects the inhibitory effect of confining pressure on the brittleness of marble more comprehensively. The brittleness index established in this paper is based on the stress state of the whole compression process and reflects the effect of different factors on rock brittleness. The accuracy and superiority of this index are verified with the experimental results.