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Abstract Based on the research on unloading rates，the triaxial unloading confining pressure tests of deep marble under different initial damage levels and unloading paths are carried out systematically. Novel unloading mechanical parameters are proposed：increment ratio of strain increment to confining pressure increment，and uniform decreasing increment of confining pressure. Combining with the dilatational parameter and plastic internal variables，the control effect of initial damage level and unloading path on failure principle of unloading deformation of deep marble is analyzed. The origin and mechanisms of the principles obtained by the unloading and failure tests are explained through an intuitive conceptual model of unloading failure. Combining with deep tunnel projects，the major guiding significance of the initial damage level principles is discussed. The research results above can provide a theoretical basis for preventing the brittle failure of hard rock under high stress conditions，e.g. rockbursts.
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Received: 15 March 2012
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2012, Vol. 31 
