边切斜裂缝岩石单轴压缩缝尖起裂机理试验研究

Experimental study on crack tip fracture initiation mechanism of straightly edge-cracked rock under uniaxial compression

为研究岩石在压剪荷载作用下的断裂特性,在岩石试样侧边切斜裂缝,预制角度分别为30°、45°、60°的初始裂纹,利用TAW-2000微机控制电液伺服岩石三轴试验机进行单轴压缩断裂试验。试验结果表明:边切斜裂缝岩石单轴压缩试样表现为明显脆性,其峰值荷载随初始裂纹角度的增大而增大,大角度初始裂纹具有更高的安全性;试样从预制裂纹尖端开始起裂,并产生向荷载作用方向扩展的翼型裂纹或反翼裂纹,缝尖裂纹扩展初期先受到压剪应力作用,随着裂纹逐渐扩展过程转变为拉应力作用,试样的最终破坏由张拉裂纹主导破坏,初始裂纹角度为45°、60°时伴随部分剪切破坏;裂纹起裂角度随初始裂纹角度的增大而呈现增大趋势,且在初始裂纹角度为60°时,同时出现了反翼裂纹与翼裂纹,起裂模式及角度的控制因素为沿扩展路径方向上法向应力值的相对大小。

In order to study the fracture characteristics of rocks under compression-shear loading, oblique cracks were cut on the side of the rock specimens with prefabricated crack angles of 30°, 45°, and 60°, and uniaxial compression fracture tests were carried out using the TAW-2000 microcomputer-controlled electro-hydraulic servo rock triaxial testing machine. The test results show that: Uniaxially compressed specimens of edge-cut diagonally cracked rock exhibit significant brittleness, with peak loads increasing with the angle of the initial crack, with large-angle initial cracks offering greater safety;the specimen starts cracking from the tip of the prefabricated crack and produces a wing-shaped crack or anti-wing crack that expands in the direction of the load action, the crack at the tip of the seam is first subjected to compressive shear stress at the beginning of the crack expansion, and then changes to tensile stress as the crack gradually expands, the final damage of the specimen is dominated by the tensile cracks, with partial shear damage accompanying the initial crack angles of 45° and 60°;the crack initiation angle tends to increase with the initial crack angle, and at the initial crack angle of 60°, anti-wing cracks and wing cracks appear at the same time. The control factor of the cracking mode and angle is the relative size of the normal stress value along the crack expansion path.