Mechanical Properties and Acoustic Emission Characteristics of Granite under Different Unloading Rates of Confining Pressures

In order to study the mechanical properties of granite under different unloading confining pressure rates, tests for the granite unloading confining pressure stress path under constant axial pressure were conducted via RMT-150B rock mechanics test system. The results show that: under the same initial confining pressure, the ductility of rock sample gets decreased with the increase of unloading confining pressure rate, which is characterized by brittle failure. The higher the unloading confining pressure rate is, the greater the strain rate is in the duration of confining pressure unloading, but the total deformation keeps small. Under the same unloading rate, the higher the initial confining pressure is, the greater the strain rate as well as the total deformation is. Then using Mogi-Coulomb intensity criterion to fit the test results, it is concluded that the unloading confining pressure rate degrades the cohesion of granite and strengthens the internal friction angle of rock; the smaller the unloading confining pressure rate is, the longer the active period of ringing count is, indicating a slow but complete development of the internal damage in granite samples under low confining pressure release rate.