Abstract This work presents the impacts of freeze-thaw (F-T) fatigue damage on the crack coalescence behaviors at the rock bridge segment for granite samples containing two unparallel flaws. The pre-existing flaw geometry in the rock was a combination of a horizontal flaw and an upper inclined flaw forming a rock bridge structure. In-situ acoustic emission (AE) detection technique and post-test X-ray computed tomography (CT) scanning were used to reveal the rock bridge fracturing characteristics during the whole deformation. Results show that both the F-T cycle and flaw inclined angle influence the crack propagation path, sample strength, deformation and AE pattern and the rock bridge fracture behavior. The AE counts and energy curves present skip phenomenon and are in consistent with the stress drop points on the macroscopic stress-strain curves. The accumulative AE energy and count decrease with increasing F-T cycles. In addition, the cracks during sample failure can be classified into six types by AE spectral frequency analysis, and the high amplitude - low frequency signal was good evident to predict the brittle fracture of the rock bridge. By the post-test CT scanning visualization of the internal crack coalescence pattern at the rock bridge segment, the most striking finding is that the rock bridge structure easily deteriorates for rock subjected to high F-T damage, which suggests that repeated F-T damage drives the crack propagation at the flaw tip and can accelerate the communication of the pre-existing flaws. The testing results are expected to enhance the understanding of the F-T fatigue damage effect on the rock bridge fracturing and can be favorable for predicting the stability of rock structures and rock mass in cold regions.

中文翻译：

---

AE监测和测后CT扫描揭示花岗岩冻融和单轴变形引起的岩桥破裂特征

摘要 这项工作提出了冻融 (FT) 疲劳损伤对包含两个不平行缺陷的花岗岩样品的岩石桥段裂纹合并行为的影响。岩石中预先存在的缺陷几何形状是水平缺陷和上部倾斜缺陷的组合，形成了岩石桥结构。采用原位声发射（AE）检测技术和测试后X射线计算机断层扫描（CT）扫描揭示整个变形过程中岩桥的破裂特征。结果表明，FT 循环和缺陷倾斜角都会影响裂纹扩展路径、样品强度、变形和 AE 模式以及岩桥断裂行为。AE 计数和能量曲线呈现跳跃现象，与宏观应力应变曲线上的应力下降点一致。累积 AE 能量和计数随着 FT 循环的增加而减少。此外，通过声发射谱频率分析，样品破坏过程中的裂缝可分为六类，高幅-低频信号对岩桥脆性断裂的预测效果很好。通过对岩桥段内部裂纹合并模式的测试后 CT 扫描可视化，最显着的发现是岩石桥结构容易受到高 FT 损伤的岩石破坏，这表明重复的 FT 损伤驱动了裂纹扩展在缺陷尖端，并可以加速预先存在的缺陷的交流。