Ductile–brittle quantitative evaluation of rock based on post-peak properties under true triaxial stress

Abstract To quantitatively evaluate the influence of high true three-dimensional stresses on ductile–brittle behaviours rock in deep underground engineering, a series triaxial compression tests with different stress levels were carried out marble and four kinds granite. The influences states ( σ 2 , 3 ) post-peak characteristics analysed, new normalized evaluation index was proposed based energy conversion under stresses. divided into qualitative levels, namely, ductile-brittleness, transitional, brittleness super-brittleness, investigated. research shows that as increases or decreases (that is, differential between increases), increases, its increase rate gradually tends to be stable, transforming from ductile-brittleness super-brittleness resulting being easily induced by low- high- conditions. When is small, intrinsic itself have an obvious behaviours. large, all rocks can exhibit super-brittle behaviour. change controls evolution behaviours, high-stress brittleness. significantly higher than conventional at same . induces causes decay decrease increasing upper limit for brittle failure rock. enhancement effect must considered when evaluating surrounding conditions; otherwise, risk may underestimated.