Experimental study on macro-micro mechanism of the marble during unloading damage process

With aim to explore unloading failure mechanism, the unloading confining pressure of marble specimens are carried out. The unloading damage process has been discussed by combining with a variety of analysis methods. The present results show: (1) During the process of unloading confining pressure, the increasing rate of strain energy is gradually increasing until specimens damage; there are inflexion point both axial strain energy curve and total strain energy curve. (2) Acoustic emission events are related to fractures variation of rock sample, the maximum value of ring-down count rate appears at the failure of rock samples, accumulated acoustic emission events appear an inflection point obviously. (3) The failure zones caused by compression have a gradually connecting trend during process of unloading tests, cracks caused by compression are in the majority of cracks. (4) The trend of concentration of shear failure is the direction that failure surfaces develop in.