含预制裂隙黑色页岩裂纹扩展过程及宏观破坏模式巴西劈裂试验研究

为研究在层理和预制裂隙共同作用下黑色页岩的断裂特性及破断机制,对含预制裂隙的圆盘试件进行巴西劈裂试验,并利用高速照相机和声发射监测装置对试件的破坏过程进行监测。结果表明:预制裂隙会削弱试件的强度,随层理和预制裂隙角度的变化,试件的强度会表现出显著的差异性。层理角度和预制裂隙角度会影响试件起裂点的位置和裂纹尖端起裂角的大小,当预制裂隙角度较小时,试件的起裂点会偏离预制裂隙尖端,裂纹沿试件中部或层理面扩展;随预制裂隙角度增大,试件起裂点逐渐转移至预制裂隙尖端,裂纹由预制裂隙尖端向应力加载方向扩展,且层理角度对裂纹起裂角的影响随预制裂隙角度增大而逐渐减弱。根据试件的裂纹形态和形成机制,可将含预制裂纹试件的破坏模式划分为5种类型,其声发射计数的时间分布特征可以划分为2种类型。同时,结合数值模拟和理论分析结果可以看出,黑色页岩表现出一定的横观各向同性特征,其层理效应随层理角度增大而增强,随预制裂隙角度增大而减弱;且最大切向应力准则可以作为预制裂隙起裂的判据。

Brazilian splitting test study on crack propagation process and macroscopic failure mode of pre-cracked black shale

In order to study the fracture mechanisms of black shale with bedding and prefabricated cracks,Brazilian splitting tests were carried out on pre-cracked disk specimens,and the fracture processes of specimens were monitored by using a high-speed camera and an acoustic emission monitoring system. The results show that the prefabricated cracks can weaken the strength of specimens and the strength of specimens shows significant difference with changing the inclination angles of the bedding and the prefabricated crack. The position of the crack initiation point and the crack initiation angle are also affected by the inclination angles of the bedding and the prefabricated crack. When the prefabricated crack inclination angle is small,the crack initiation point deviates from the prefabricated crack tip and the crack propagates along the middle or the bedding surface of specimens. With increasing the prefabricated crack angle,the crack initiation point gradually transfers to the prefabricated crack tip and the crack propagates from the prefabricated crack tip to the loading direction. Moreover,the effect of the bedding inclination angle on the crack initiation angle decreases gradually with increasing the prefabricated crack inclination angle. According to the morphology and generation mechanism of cracks,the failure mode can be divided into five types and temporal distribution of acoustic emission count can be divided into two types. By combining the results of numerical simulation and theoretical analysis,it can be seen that the black shale shows certain transverse isotropic characteristics,that the bedding effect increases with increasing the bedding inclination angle and decreases with rising the prefabricated crack angle,and that the maximum tangential stress criterion can be used as the criterion for the initiation of prefabricated cracks.