Aiming at brittle failure of hard rock(taking limestone for example)

true triaxial and acoustic emission experiments are adopted to study the mechanical characteristics

deformation and failure mechanisms

characteristics of acoustic emission(AE) activities and law of energy release. The experimental results indicate: (1)Under the unloading stress path

strength of specimens is apparently effected by unloading

and varies in intervals along with the intermediate principal stress. Failure modes of most specimens are splitting. (2)Under the unloading-supporting stress path

the mechanical properties of rock are significantly improved by supporting force. The main failure mode is tensile shear failure. (3) The whole process of AE activity can be divided into 3 active stages (crevasse crack closing stage

unloading damage stage and destruction stage) and 2 relatively quiescence stages (elastic stage and fracture stable development stage). The characterization parameter “absolute energy” of AE can quantitatively describe the brittle failure of hard rock. The results of experiments are similar with rock mass behaviors and support effect in project field so as to provide test basis and guide instruction for engineering practice.