Influence of specimen dimensions on bursting behaviour of rocks under true triaxial loading condition

摘要

Rockburst is a sudden violent ejection of rock fragments from the free surface created during excavation of a tunnel, drifts or any underground openings. Due to deep mining and/or tunnelling activities under high pressure and temperature conditions, the occurrence of rockburst is getting more frequent and prevalent, which may result in catastrophic failures and fatalities. Therefore, understanding the mechanism of rockburst phenomenon has a paramount importance for safe underground construction. In the last decade, true triaxial testing system has been widely used to understand rockburst by replicating in situ stress states before and after the excavation in the laboratory. In these tests, rectangular prism or cubic specimens are commonly used. However, no specifications for specimen dimensions and aspect ratios are recommended by the International Society for Rock Mechanics (ISRM) or the American Society for Testing and Materials (ASTM)for a standard rockburst test. In this study, we have collected a comprehensive database from the literature to evaluate influence of specimen dimensions on results of rockburst test for a potential development of standard samples dimensions. The effects of dimensions of rectangular rock prisms with different height-to-width (H/W), height-to-thickness (H/T) and width-to-thickness (W/T) ratios on the rockburst failure were investigated and the failure modes with respect to various aspect ratios were evaluated in terms of stored strain energy in p-q space. It was found that, H/W ratio has the most significance influence on the failure mode regardless of the stress states. Dynamic failure of the specimens was transformed from spalling and splitting (local rock ejection) to slabbing and bursting (full-face bursting) when the H/W ratio increases and bursting behaviour becomes more violent.