双轴加载下花岗岩破裂过程声发射b值特征研究

Study on the characteristics of AE b-value during granite failure process under biaxial loading

基于声发射定位技术开展了双轴加载条件下岩石破裂声发射b值变化规律试验研究。研究结果表明:声发射率峰值对应的应力与峰值应力的比值k随着侧向应力的出现呈减小的趋势,侧向压力为0时,k值约为0.87;侧向压力为5~25 MPa时,k值明显低于0.8。岩样声发射b值先随应力增大而增大,之后随应力增大而减小。随着侧向压力的增大,声发射b值峰值出现在较低应力区间,侧向压力为0时,轴向应力达到轴向峰值应力的80%,b值开始下降;侧向应力为5~25 MPa时,b值峰值对应的轴向应力明显小于轴向峰值应力的80%,这是因为侧向应力使试样更早达到声发射率峰值,更早进入裂纹不稳定扩展阶段。研究成果对于理解双轴加载条件下岩石的破坏具有重要意义。

Based on the acoustic emission(AE)locating technology,the experiment study of fracture mechanism and time and space distribution characteristics of the change of b-value for granite rock acoustic emission under biaxial compression is conducted.The results show that k value,the ratio between axial stress corresponded by peak AE rate and axial compressive strength,shows a decreasing trend with the appearance of the lateral pressure.When lateral pressure is zero,k value is about 0.87.When the lateral stress is 5~25 MPa,k value is obviously lower than 0.8.The change rule of b-value in the biaxial experiment increases firstly,then decreases with the stress increasing.With the increasing of the lateral pressure,the peak of b-value appears in lower stress range.Without the lateral stress,b-value begins to decrease when the axial stress reaches 80%of the axial peak stress.When the lateral stress ranges from 5 to 25 MPa,the axial stress corresponding to the peak of b-value is apparent less than 80%of the axial peak stress.This is because the lateral pressure makes samples reach the peak AE rate earlier and enter the unstable stage of crack propagation earlier.The research results are of great significance to understand rock failure under biaxial loading.