Independence verification of peak-strength strain energy storage index from rock specimen shape effects

The strain energy storage index ( W ET ) is a crucial index for evaluating rockburst proneness. Interestingly, when conducting tests to obtain W ET , variations exist in the shape of coal or rock specimens. However, whether shape factors affect W ET has not been theoretically and experimentally verified. In this study, to investigate the independence of W ET from specimen shape effects, its rationality was first theoretically derived based on the linear energy storage (LES) laws of rock, indicating that W ET is influenced by the energy storage coefficient (ESC) of the rock. Two typical rock materials (granite and red sandstone) with different rockburst proneness were selected to verify the migration effect of cubic and cylindrical specimens on W ET via uniaxial compression tests. The experimental results revealed that the mechanical behavior characteristics of rocks were affected by the shape of cylindrical and cubic specimens, whereas the W ET and ESC were opposite. Furthermore, the practical W ET values closely approximate the theoretical values of energy storage-dissipated ratio predicted by the LES law, converging to the peak-strength strain energy storage index ( ). Based on the LES law, the influence of specimen shape on W ET and was further discussed, concluding that W ET and are independent of specimen shape effects. Furthermore, the is more stable than W ET and reflects the relative magnitude of energy storage and dissipation during the entire pre-peak of rock. Thus, the peak-strength strain energy storage index can be used as a substitute for W ET in evaluating the rockburst proneness of rock. • The experimental migration effect of W ET in rock shapes is proved using the linear energy storage law. • W ET is unstable and theoretically converges to the peak-strength strain energy storage index ( ). • W ET and are independent of rock shape effects and only affected by the energy storage coefficient of rock. • The can be used as a substitute for W ET in evaluating the rockburst proneness.