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Abstract Damage and dilation characteristics of the granite from great depth at Beishan under triaxial cyclic loading-unloading conditions were investigated using the rock mechanical test machine MTS815 and the acoustic emission(AE) measurement system PCI–2. Complete stress-strain curves associated with the accumulative AE hits and the 3D distributions of AE events were analyzed. The mechanisms of fracture evolution of the rock samples during deformation were revealed. The variation of dilation angle with plastic shear strain was characterized and the confining stress dependent dilation behavior was discussed according to the established plastic strain locus. The 3D distributions of AE events in the process of loading-unloading indicated that the maximum gradient of crack growth occurred at the stage of strain softening. In this stage，the cyclic loading was the main factor triggering the drastic damage and the macro coalescence of fractures in the rock. At the stage of residual deformation，there were almost no newly generated cracks. The incremental AE events at this stage were primarily attributed to the frictional sliding of the shear plane. This explained why the volumetric strain rate approached zero near the end of loading. Compared with the loading process，the repeated unloading had smaller effects on the development of cracks. Due to the different states of crack propagation，a significant difference in AE characteristics before and after the crack damage stress( ) were observed. The calculated post-peak dilation angle deceased with the increasing of the plastic shear strain and its decaying gradient decreased with the increase of the confining stresses. A model for dilation angle was established using an exponential function to reasonably describe the dilation behaviors of Beishan granite.
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Received: 05 May 2014
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2014, Vol. 33 
