The timing and location of microcracking events, their propagation and coalescence to form macrocracks, and their development by tension, shearing or mixed modes are little known but essential to understanding the fracture of intact rock by freezing and thawing. The aims of the present study are to investigate the mechanisms and transition of microcracking and macrocracking during repeated freeze-thaw, and to develop a statistical model of crack propagation that assesses the distance and angular relationship of neighboring cracking events arranged in their temporal order of occurrence. Eight acoustic emission (AE) sensors mounted on a 300 mm cubic block of chalk captured the three-dimensional locations of microcracking events in their temporal order of occurrence during 16 seasonal freeze-thaw cycles simulating an active layer above permafrost. AE events occurred mostly during thawing periods (45%) and freeze-to-thaw transitions (37%) rather than during freezing periods (9%) and thaw-to-freeze transitions (8%), suggesting that most AE (microcrack) events were driven by the process of ice segregation rather than volumetric expansion. The outcomes of a novel statistical model of crack propagation based on two boundary conditions—inside-out and outside-in modes of cracking—were assessed based on Bayes’ theorem by testing the hypothesis that the inside-out mode of cracking was favored by tensional activity, whereas the outside-in mode was supported by shearing events. In both situations, the hypothesis accounted for 54%–73% confidence level. The microcrack propagation model can distinguish reasonably between cracks formed by volumetric expansion and ice segregation.

中文翻译：

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通过冷冻和解冻过程中的声发射分析对石灰石中裂缝传播动力学的实验观察和统计建模

微裂纹事件的时间和位置、它们的传播和聚结形成宏观裂纹，以及它们通过张力、剪切或混合模式的发展鲜为人知，但对于理解完整岩石通过冻结和融化而破裂是必不可少的。本研究的目的是研究反复冻融过程中微裂纹和宏观裂纹的机制和转变，并开发裂纹扩展的统计模型，以评估按发生时间顺序排列的相邻裂纹事件的距离和角度关系。 . 八个声发射 (AE) 传感器安装在 300 毫米立方白垩块上，在模拟永久冻土上方的活动层的 16 个季节性冻融循环期间，按照发生时间顺序捕获微裂纹事件的三维位置。AE 事件主要发生在解冻期 (45%) 和冻融转变 (37%) 而不是冻结期 (9%) 和解冻到冻融转变 (8%)，表明大多数 AE（微裂纹）事件是由冰分离过程而不是体积膨胀驱动的。基于贝叶斯定理，通过检验由内向外开裂模式受张力偏爱的假设，评估了基于两种边界条件（内向外和外向内开裂模式）的新型裂纹扩展统计模型的结果。活动，而外向模式由剪切事件支持。在这两种情况下，假设占 54%–73% 的置信水平。微裂纹扩展模型可以合理区分体积膨胀和冰偏析形成的裂纹。