Study on damage characteristics and mechanical properties of limestone under multiple impact loads

In order to study the safety of limestone under multiple impact loads.The split Hopkinson compression bar device with a diameter of 50 mm was used to carry out impact compression tests on the specimens under different strain rates and different impact times.Combined with ultrasonic testing device, the longitudinal wave velocity of rock mass under load was measured.The variation laws of longitudinal wave velocity, damage factor, peak stress and energy dissipation of rock mass were analyzed.The results show that the longitudinal wave velocity of limestone specimen decreases with the increase of impact times, and the decrease of wave velocity is increasing with the increase of damage factors.It takes 6 times to break the specimen under the action of 0.25 MPa impact pressure, and 4 times to break the specimen under the action of 0.35 MPa and 0.40 MPa impact pressure.The increase of impact pressure reduces the impact times used to damage the rock mass.Under the impact pressure of 0.40 MPa, the peak stress of the specimen under the second, third and fourth impact decreases by 6.23%, 14.00% and 25.92% respectively.The impact reduces the peak stress of specimen, and the stress of the specimen decreases greatly under the later impact.The energy time history of rock mass under impact load is divided into three stages.There is a quadratic linear positive correlation between the energy consumption density of rock mass crushing and the impact times.When the impact pressure is 0.40 MPa, the energy consumption density of rock mass under the second, third and fourth impact is 1.06, 1.38 and 1.78 times that of the first impact.The damage effect of impact on rock mass in the later stage is more significant.