不同试验条件和含水状态下花岗岩的声发射与破裂演化特征

Acoustic Emission and Fracture Evolution Characteristics of Granite under Different Testing and Moisture Conditions

为进一步揭示含水岩石破裂演化机制和裂纹扩展规律,开展了不同含水状态花岗岩的单轴压缩试验、巴西劈裂试验和直剪试验,得到了岩石在变形破坏过程中的力学、声学信息,结合声发射振铃计数和特征参数(RA)与平均频率(AF)的相对关系,厘清了含水花岗岩在不同试验条件下的微观破裂特征。结果表明:水对岩石的抗压、抗拉、抗剪强度以及弹性模量均有明显的弱化作用;不同试验条件下花岗岩的声发射信号存在明显差异,单轴压缩条件下声发射振铃计数在峰值应力点附近激增且信号活动主要出现在峰值应力点后,巴西劈裂条件下声发射振铃计数的整体波动相对较小,直剪试验条件下振铃计数激增现象比单轴压缩明显提前,呈阶梯式增长;单轴压缩条件下张拉裂纹数量呈现先减少再增加的趋势,而剪切裂纹始终在减少,直剪试验条件下剪切裂纹占主导作用,巴西劈裂条件下张拉裂纹占主导作用;不同试验条件下水对花岗岩剪切裂纹和张拉裂纹的影响机制类似,水会促进岩石内部张拉裂纹的发育而抑制剪切裂纹的发育。研究结果可为进一步探究工程围岩在不同应力场下的破裂特征提供一定的参考依据。

To reveal the fracture evolution mechanism and crack propagation law of water-bearing granite,uniaxial compression,Brazilian splitting and direct shear tests of granite with different water-bearing states were carried out.The mechanical and acoustic information of rock during deformation and failure were obtained.Combined with acoustic emission ringing count and the relationship between RA(ratio of rise time to amplitude)and AF(average frequency),the microscopic fracture characteristics of water-bearing granite under different test conditions were clarified.The results show that water has obvious weakening effect on the compressive strength,tensile strength,shear strength and elastic modulus of rock.There are significant differences in acoustic emission activities of granite under different test conditions.Under uniaxial compression,the ringing count of acoustic emission surges near the peak stress point and the signal activity mainly occurs after the peak stress point.Under Brazilian splitting condition,the overall fluctuation of the ringing count of acoustic emission is relatively small.Under direct shear test,the ringing count surges significantly earlier than that of uniaxial compression and increases in a stepwise manner.The influence mechanism of water on shear cracks and tensile cracks of granite under different test conditions is similar,that is,the presence of water increases the number of tensile cracks in the rock and reduces the number of shear cracks.In uniaxial compression,tensile cracks show a trend of decreasing first and then increasing,while shear cracks are always decreasing.Shear cracks play a leading role in the direct shear test,and tensile cracks play a leading role in the Brazilian splitting.The research results provide some reference for further study on the fracture characteristics of engineering surrounding rock under different stress conditions.