Deformation and Failure Characteristics of Loading and Unloading Rock Based on Volume Crack Strain

In order to study the laws of crack evolution in rock and explain its fracture instability mechanism, a series laboratory tests were carried out with Jinping Marbles. The test results show that failure degree marbles under unloading conditions is more severe than loading conditions. Based on volume strain, five progressive stages different are divided, corresponding characteristic stresses determined. pre-peak propagation strain without considering initial damage used evaluate growth rock, it found lower confining pressure, higher rate rate, less cracks generated before peak, prone brittle after peak. starting point sharp increase proposed as precursor point, stress levels 70%–100%, which decrease rise. Under conditions, points appear later close rocks sudden failure.