Evaluation of rock brittleness based on the ratio of stress drop rate to strain drop rate and peak strength.

This paper aims to overcome the imitations of the existing indices in the evaluation of rock brittleness. Considering the importance of brittleness evaluation in rock engineering, this paper analyses the existing brittleness indices against brittleness features like strength, stress-strain curve, hardness, mineral composition, internal friction angle, elastic modulus, Poisson's ratio, etc., revealing that each approach has its strengths and weaknesses. For instance, the index of rupture angle is too difficult to identify accurately, while the indices based on stress-strain curve are easy to obtain and quantify. On this basis, a new brittleness index (BL) was proposed based on the ratio of stress drop rate to strain drop rate (drop rate ratio0 and the peak strength. Then, the proposed index was validated through uniaxial and triaxial compression tests, and compared with B8, B11 and B12. It is concluded that the proposed index could accurately identify rock brittleness under different confining pressures, and outperform other indices in revealing the variation of rock brittleness; the index could also accurately reflect the brittle anomalies of the rock specimen at the confining pressure of 15MPa, making it a desirable tool to evaluate rock brittleness under uniaxial compression. [ABSTRACT FROM AUTHOR]