Seminar

Study on rock fracturing characteristics is of fundamental significance in solving rock engineering problems as well as better understanding geological processes. As we know, the macroscopic fracturing characteristics of rock are largely influenced by its microstructural features. Here, we investigated the effects of microstructures on the fracture mechanical properties of granite. Mode I fracture toughness tests were performed on three types of Hong Kong granite with various grain size based on the semi-circular bending (SCB) method. The results show that grain size is the most sensitive microscopic factor controlling the fracturing characteristics for the three studied granite. The measured mode I fracture toughness values decrease with the increase of average grain size. The failure modes change from brittle to ductile as the grain size increases. Acoustic emission (AE) technique was utilized to monitor the evolution of the microcracking process. The width and length of the fully developed fracturing process zone have positive and negative relations with the grain size, respectively. In addition, the medium-grained granite has the relatively longest rapid microcrack developing period, which seems to be related to more pre-existing microcracks. Before the final failure, the AE event rate is observed to drop drastically accompanied by a rapid increase of AE energy rate for all the granite types, which is seen as an important precursor of macroscopic crack initiation under the mode I loading condition.