深部岩体力学与开采理论研究进展

为研究石灰岩在多次冲击荷载作用下的安全性，采用直径为50 mm的分离式霍普金森压杆装置对石灰岩试件开展不同应变率及不同冲击次数下的单轴冲击压缩试验，并结合超声波检测装置测量多次冲击荷载作用下岩体纵波波速，分析岩体纵波波速、损伤因子、峰值应力及能量耗散变化规律。结果表明：石灰岩试件纵波波速随冲击次数的增加而降低，波速降幅不断增大，损伤因子随之增大；0.25 MPa冲击气压作用下试件破碎需要6次，0.35、0.40 MPa冲击气压作用下试件破碎需要4次，冲击气压的增大使岩体产生破坏所用冲击次数减少；0.40 MPa冲击气压第2、3、4次冲击作用下试件峰值应力降幅分别为6.23%、14.00%、25.92%，冲击作用使试件峰值应力降低，且后期冲击作用下试件应力降幅增大；冲击荷载作用下岩体能量时程曲线分为3个阶段，岩体破碎耗能密度与冲击次数之间呈现良好的二次线性正相关关系，0.40 MPa冲击气压第2、3、4次冲击作用下岩体耗能密度是第1次的1.06、1.38、1.78倍，后期冲击作用对岩体的破坏作用更加显著。

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.