Influence of loading rate on strainburst: an experimental study

Rockburst is a geological disaster in highly stressed ground. As a typical rockburst, strainburst is an ejection failure phenomenon caused by tangential stress concentration, which is frequently encountered in hard-brittle intact rocks in deep tunnel excavation. To explore the strainburst characteristics, a set of tests on rectangular prismatic granite specimens with different loading rates were conducted using an improved true-triaxial testing machine. During the testing process, a special loading path, namely, keeping one free face and loading on other faces, was adopted to simulate the stress concentration of surrounding rock masses near the opening. High-speed cameras were used to record the failure process on the free face of tested specimens. The speed and the kinetic energy of ejected fragments during strainburst were obtained by analyzing videos recorded using high-speed cameras. The experimental results reveal that the loading rate (simulating the rate of tangential stress concentration) plays an important role with respect to the strainburst characteristics. As the loading rate increases from 0.05 to 5.0 MPa/s, the failure mode of tested specimens transfers from static failure (spalling) to dynamic failure (strainburst), and the kinetic energy of ejected fragments during strainburst, as well as the rock strength, increases.