Microcracking behavior of granite with different textural properties under mode i loading

Abstract

Granite is a common intrusive igneous rock in the earth's upper crust. Its texture depends on its cooling history and the tectonic environmental conditions. The macroscopic mechanical properties of granites have been recognized to be strongly controlled by their textural and microstructural properties. However, little is known about the influence of these features on the microcracking behavior. To this end, we experimentally investigate the microcracking behavior of three granites (fine-, medium-, coarse-grained) with different textural properties subjected to mode I loading based on the semi-circular bending (SCB) tests. Detailed thin-section analysis is conducted to quantitatively describe the microstructural features of the granites. The evolution of microcracks is monitored by recording the acoustic emission (AE). Based on the AE signatures, four phases of the microcracking process of the SCB specimens, namely initial quiet phase, slow AE development phase, fast AE development phase, and post-failure phase are identified. The fracture process zones (FPZs) differ among three granites in terms of their development styles as well as the fully-developed FPZ characteristics. We find that the medium-grained granite, which possesses more pre-existing microcracks, has the longest rapid AE development phase and the largest maximum AE event density of the fully-developed FPZ among the three granites. The maximum width of the FPZ increases with the increase of the grain size. For all the three granites, most of the AE energy is released during the FPZ development period. As the FPZ is fully developed at the end of this period, a relatively larger amount of energy is released at a few AE event locations, which is plausibly related to the coalescence of microcracks before the development of the macroscopic fractures. Our study contributes to a better understanding of how the microstructural properties of granite influence its microcracking behavior.