Study on energy concentration and dissipation of Beishan granite in Gansu during failure process

Servo test system was used to obtain stress-strain curves of Beishan granite under different confining pressure, and the loading process was jointly controlled by means of axial pressure and circumferential deformation.Variation characteristics of energy and characteristic stress of Beishan granite were researched.Characteristic stress are linear increase with confining pressure increasing, crack initiation stress, damage stress and peak strength increased 3.30 MPa, 6.74 MPa, 7.68 MPa respectively along with confining pressure increased 1 MPa.Total energy and elastic energy corresponding to characteristic stress are greatly increase with confining pressure increasing.When confining pressure increased form 2 MPa to 30 MPa, elastic energy corresponding to initiation stress, damage stress and peak stress increased 5.2 times, 5.8 times and 5.1 times respectively, corresponding total energy increased 4.9 times, 5.7 times and 4.7 times respectively.The increment of dissipation energy increase with increasing of confining pressure, and energy at the crack unstable propagation stage was significant affected by confining pressure.Energy storage coefficient was defined to estimate rock stability around the peak strength, effect of stress state coefficient on energy storage was further analyzed.