Abstract: The deformation and fracture of rocks are an evolution process with the exchange of energy and mass between rocks and outer exotic environment.Rock failure is a state failure phenomenon driven by energy.The axial stress increases rapidly during excavation and it tends to be stable with the increasing of time,but confining pressure is unloaded instantaneously.At present,indoor test scheme mainly adopts increasing axial pressure and reducing confining pressure at the same time or keeping axial pressure constant and reducing confining pressure.The experimental results show that:the confining pressure effect of rock failure is significant,the total strain energy,elastic strain energy and dissipation energy are positively correlated with the initial confining pressure;with the increasing of the unloading rates,the energy conversion rates is decreased continuously,and the phenomenon of transient dynamic failure can be appeared easily;the difference of energy evolution is significant under the different unloading levels;the larger the fractal dimension,the more obvious dilatancy,the more developed of transgranular and intergranular cracks and the more energy is consumed.Based on the existing study results,the development trend of testing system improvement,adopting the stress path in accordance with engineering practice,study of micro-meso crack and further study of the sensitive stage of energy conversion are proposed as the further study directions.

Key words: Rock mechanics, Unloading, Damage, Energy evolution, Failure