天然岩体中常出现相交节理裂隙I/II/III混合模式裂缝。在深部地下工程中,节理岩体在长期承受地应力时容易发生岩爆。然而,这些相交接头的力学机制的大多数研究都是通过简化二维接头模型试验进行的。此外,二维交叉关节在拉伸和压缩作用下的断裂机制与三维关节完全不同。本文介绍了一种新型的预制试样,该试样具有相交接头的组合,能够检测蠕变载荷下岩石I/II/III混合模式裂缝的破坏行为。对相交节理为0°/0°的预制砂岩试件进行了单轴压缩和多级蠕变试验,0°/30°,0°/60°,0°/90°。实验结果表明,随着预制交叉节点数量的增加,砂岩试件的单轴抗压强度和弹性模量值逐渐降低。此外,砂岩试样在多级蠕变试验的第一蠕变阶段和第二蠕变阶段经历相对较少的AE事件和较小的轴向应变变化。由于第三蠕变阶段中AE事件的数量急剧增加,轴向应变急剧增加。0°/60°砂岩试件加速蠕变破坏,导致混合X形拉伸剪切断裂。基于使用上升角(RA)和平均频率(AF)的声发射参数对蠕变裂纹的量化,RA值很高。0°/0°的AF值,0°/30°,0°/90°砂岩标本较高。实验结果表明,较大的节理相交角会导致较大的相互约束,对岩石试样中预制裂纹扩展的影响更大。从而增加最终的破坏强度。最后,根据声发射计数,建立了适合于表征节理岩体蠕变损伤演化的特征变量D。本文的研究结果有助于有效理解I/II/III混合模式断裂的蠕变效应及其微观机理。研究成果对瞬时和时滞岩爆的探测和风险缓解具有一定的参考价值。
I/II/III mixed mode fractures of intersecting joint fissures often occur in natural rock masses, and jointed rock masses are prone to rockbursts in deep underground engineering when subjected to long-term crustal stresses. However, most studies of the mechanical mechanisms of these intersected joints have been conducted by simplifying two-dimensional joint model tests. Furthermore, the fracture mechanisms of two-dimensional intersected joints under tension and compression are completely different from those of three-dimensional joints. This paper presents a novel prefabricated specimen with combinations of intersecting joints capable of detecting the failure behaviours of rock I/II/III mixed mode fractures under creep loading. Uniaxial compression and multistage creep tests are performed on prefabricated
sandstone specimens with intersecting joints of 0°/0°, 0°/30°, 0°/60°, and 0°/90°. The experimental results show that with the increase in the number of prefabricated intersecting joints, the uniaxial compressive strength and elastic modulus values of the
sandstone specimens gradually decrease. In addition, the
sandstone specimens experience relatively few AE events and minor axial strain variations in the first creep stage and the second creep stage of the multistage creep test. The axial strain increases sharply due to the sharp increase in the number of AE events in the third creep stage. The 0°/60°
sandstone specimen undergoes accelerated creep failure, resulting in mixed X-shaped tensile‒shear rupture. The RA value is high based on the quantification of the creeping cracks using the acoustic emission parameters of the rise angle (RA) and average frequency (AF). The AF values of the 0°/0°, 0°/30°, and 0°/90°
sandstone specimens are high. The experimental results show that a larger joint intersection angle leads to greater mutual restraints and greater effects of prefabricated crack propagation in the rock specimens, thus increasing the final failure strength. Finally, based on the acoustic emission count, a characteristic variable D suitable for characterizing the creep damage evolution of a joint rock mass is established. The findings of this paper can facilitate an effective understanding of the creep effect of I/II/III mixed mode fracture and its micromechanism. The research results will have a certain reference value for the detection and risk mitigation of instantaneous and time-delayed rockbursts.