考虑层理影响页岩巴西劈裂及声发射试验研究

Effect of bedding plane direction on acoustic emission characteristics of shale in Brazilian tests

基于不同层理角度的页岩巴西劈裂试验,利用高速摄像系统和声发射系统,对页岩力学特性、裂纹扩展及声发射特征的层理效应进行了深入研究。结果表明：（1）页岩巴西劈裂破坏过程可以分为压密、弹性和破坏3个阶段;（2）页岩抗拉强度、劈裂模量和应力峰值时变形的各向异性特征明显,层理角度θ=30°时,层理效应最为明显,θ=90°时影响最小;（3）θ=0°和θ=15°时试样的裂纹破坏面基本是沿着层理面,θ=30°时裂纹面交切层理面,与加载基线面重合,θ=45°～90°的各试样的断裂面呈不同程度的偏离加载基线面,为弧面或曲面;（4）θ=30°和θ=45°为破坏机制转化角,其中θ=30°为沿着层理面压致性张拉开裂转化为交切层理面开裂的转化角,θ=45°为交切层理面开裂转化为交切层理面且沿着层理面不同程度的剪切滑移开裂的转化角;（5）声发射活动性和能量释放随层理角度的增加而加强,主要因为受层理角度的影响,其破坏机制不同,这也进一步验证了页岩随层理角度的变化,其破坏机制的各向异性。能率峰值与抗拉强度具有很好的线性关系,表明声发射能率峰值能很好地反映岩石抗拉伸破坏的程度。

Brazilian tests are conducted on shales with different bedding angles, and a high speed camera and an acoustic emission（AE） system are used to investigate the effect of stratification on shale mechanical properties, crack propagation and AE characteristics. The results indicate that：（1） Brazilian split destruction process can be divided into three stages： compaction stage, elastic stage and destruction stage.（2） The anisotropic characteristics of tensile strength, splitting modulus and deformation at the stress peak point are highly distinct. The most obvious effect of stratification is found at the angle of θ=30°, whereas the smallest effect is found at the angle of θ=90°.（3） For samples with angles of θ=0° and θ=15°, the failure surfaces are normally along the direction of bedding plane. At the angle of θ=30°, the failure surface intersects bedding planes and coincides with the loading baseline surface. In contrast, fracture surfaces deviate from the loading baseline surface with varying degrees and turn out to be curved surface for samples with angles of θ= 45°, 60°, 75° and 90°.（4） θ=30°and θ= 45° are transformation angles of failure mechanisms. At θ= 30°, tension failure occurs along bedding converts to cross-cut bedding plane failure along the loading baseline, while cross-cut bedding plane failure happens along the loading baseline converts to cross-cut bedding planes failure with varying degrees of shear slip at θ=45°.（5） AE activities and energy releases demonstrate obviously with increasing bedding angles caused by the bedding plane, which results in the anisotropy of failure mechanism. Moreover, there exists a good linear relationship between the peak value of AE energy rate and tensile strength, which indicates that the peak value of AE energy rate can reflect the variation of tensile strength well.