Abstract: Rock residual strength is a critical parameter for engineering projects such as tunnel excavation, mining operations, and slope stabilization. The calculation of residual strength using strength criteria often yields inaccurate results, and the required parameters are difficult to obtain. In this study, we introduce the energy reduction ratio parameter to quantify the strength reduction and propose a novel method for determining residual strength. To validate the method, triaxial compression tests were conducted on sandstone samples in a region. The results indicate a significant negative correlation (0.943) between the energy reduction ratio and confining pressure. Subsequently, experimental data from 20 different rock types were collected and analyzed. Compared with two existing methods, the proposed method provides more accurate calculations of rock residual strength. Based on the slope characteristics of the energy reduction ratio fitting curve, two distinct types of curves can be identified: concave downward and convex upward curves. Finally, the correlation between these curve types and rock brittleness-ductility transitions, as well as their relationship with rock failure modes, is established. These findings offer valuable references for evaluating the stability of rock mass engineering.

Key words: residual strength, energy parameter, energy reduction ratio, triaxial test, rock failure