Abstract: In order to study energy release and ejection velocities of rock fragments induced by pillar rockburst in rock mass engineering, pillar model specimens are designed and prepared with three different types of rock materials. The ejection processes of rock fragments in failure are recorded by the high-speed camera in uniaxial compression tests; and the ejection velocities of rock fragments are calculated with experimental data. Based on Griffith' energy release theory, the released energy in failure of test models are calculated by ANSYS finite element software under both plane stress and plane strain; and the theoretical ejection velocities of fragments are calculated by the principle of conservation of energy after removing a certain percentage of energy dissipation. The results show that the compressive strength, elastic modulus, and rockburst proneness, as well as the released energy and ejection velocity of fragments increase sequentially (following the sequence of red sandstone, shidao red granite and camellia white granite). The failure degree is severer for the pillars with the larger width. The energy release under the plane strain condition (which is closer to the pillars in the field engineering) is greater than that under the plane stress condition(which is closer to the tests in this study). Therefore, the compressive strength, elastic modulus of rock materials and the shape and size of rock structure determine the disaster degree of pillar rockburst. The theoretical ejection velocities of fragments are basically close to the measured velocities in model tests on pillar rockburst. Without considering the size effect, it is proved that the ejection velocity occurred in the large-scale model (engineering scale) is basically equal to that in the small-scale model(test scale) under the same stress condition.

Key words: pillar rockburst, model test, finite element calculation, energy release, ejection velocity