2003 Volume 14 Issue 3 Pages 241-247
In underground construction projects such as radio activate waste disposal facilities, clarification of the rock failure mechanism is an important, though difficult task. Although many informative studies have been published on this topic, additional research is needed to help keep these structures stable for many years. In this study, microcracks were firstly identified by the fluorescent method and next classified in detail in order to analyze the relationships and processes in crack growth and junction. That is, microcracks are classified into three kinds of cracks: intracrystalline cracks, intercrystalline cracks and grain boundary cracks. In spite of the complicated features of cracks, these detailed classifications became possible by image processing.
Observed crack directions and length (total length / mm2) became more characteristic as lateral strain increased especially in post-failure specimens. At first, the number of intracrystalline cracks and grain boundary cracks increased slowly, and intercrystalline cracks did not increase much. Intercrystalline cracks, however, increased in number around junctions and rapidly increased after junction in the typical three directions and in total length. On the other hand, intracrystalline cracks and grain boundary cracks almost stopped growing after junction. Thus, we found that intercrystalline cracks have a quite important role in the sharing process, although they are less numerous than other crack types.
Because of the complicated images, fractal dimensions were also measured by box counting method in these stages. Though intracrystalline cracks and grain boundary cracks showed almost the same fractal dimensions throughout the failure process, intercrystalline cracks increased in number especially in post-failure specimens, suggesting intercrystalline cracks have an important role in the failure process. In fractal dimensions, the same trends were seen.
