Nonlinear energy storage and dissipation of rocks are common in earthquake, tunnel, and mining engineering. To investigate the nonlinear energy characteristics of rocks, multi-level cyclic loading–unloading triaxial compression (CLTC) tests were performed on early Cretaceous granite and Permian red sandstone. The failure modes of the granite and sandstone specimens under CLTC tests were studied. The energy parameters, such as the input, elastic, and dissipated energy densities (IE, EE, and DE, respectively), of the two types of rocks under different confining pressures were calculated, and the nonlinear interrelations among the three energy parameters were investigated. The results indicated that in the CLTC tests, the failure modes of sandstone were all shear failure. The granite specimens in the CLTC tests failed via splitting. The confining pressure had no effect on the peak strength strain energy storage index at the failure of the rock specimens, which tended to be constant. The nonlinear evolution of the DE of the granite and sandstone with respect to the EE and IE in the CLTC process was divided into three stages: an initial stage, a linear stage, and an accelerated stage. Furthermore, according to the nonlinear energy-conversion mechanism, a self-inhibition energy-conversion model was established in consideration of the confining-pressure effects. Using this nonlinear energy-conversion model, the EE and DE at any strain level can be determined. The peak strength strain energy storage index was calculated to evaluate the rockburst proneness of granite and sandstone. The results agreed well with those of the uniaxial compression test.

This paper on a criterion for rockbursts is focused mainly on the stress concentration and gradient change of the tangential stress of the surrounding rock. Two parameters are introduced into tunnelling strain rockburst prediction: the radius of the plastic zone and the radial stress at the elastoplastic junction after excavating the surrounding rock. A new rockburst criterion is proposed based on the mechanism for throwing-type rockbursts and catastrophe theory. Meanwhile, a new multi-factor index for identifying rockburst classification is given based on rockbursts in actual engineering. The results show that there is a certain correlation between strain rockbursts and the plastic-zone radius and radial stress of the surrounding rock, which can be estimated using the mechanical parameters and stress distribution before excavation, whereupon strain rockbursts can be predicted. By dividing the rockburst interval through a large number of rockburst examples, the accuracy of the criterion reaches 80.36%, and the accuracy for moderate-to-strong rockbursts reaches 83.33%.