The Evolutionary Distribution Law of Rock Energy and the Study of Energy Balance Mechanism in Tunnel-Surrounding Rock

In this study, triaxial cyclic loading–unloading tests are conducted on sandstone samples under four different confining pressures to examine the energy evolution and distribution characteristics of brittle rocks subjected to cyclic loading. Two methods for energy calculation, namely the integration of single loading–unloading curves and the consideration of cyclic fatigue damage, are employed to elucidate the energy evolution patterns and the effects of confining pressure on loaded rock samples. A criterion for predicting rock instability is developed based on the cumulative impact of dissipated energy. An analysis of energy storage characteristics indicates that the internal energy storage of rocks follows a power function relationship with stress levels and a linear function relationship with confining pressure. By integrating energy conservation principles with elastoplastic analysis, the energy balance mechanism and the transfer-transformation law of tunnel surrounding rock under elastic–brittle–plastic constitutive conditions are derived and examined, facilitating the application of rock energy theory to practical engineering scenarios. Engineering analysis demonstrates that external energy is transmitted from the deeper sections of the surrounding rock to the excavation area of the tunnel through radial stress work. At the elastic–brittle interface, both elastic and dissipated energy experience abrupt changes while strictly conforming to the law of energy conservation. The findings of this research offer a theoretical basis for the support design of rockburst tunnels and impulsive ground pressure tunnels.