A computational method for tunnel energy evolution in strain-softening rock mass during excavation unloading based on triaxial stress paths

The squeezing deformation of deep soft rock tunnels is driven by energy. Few scholars have carried out theoretical research on energy evolution for deep soft rock tunnels. This study proposes a computational method for tunnel energy evolution in strain-softening rock mass during excavation unloading based on triaxial stress paths. The characteristics of energy distribution and energy evolution are further investigated. Results show that energy is input from the distant surrounding rock after tunnel excavation and converted into elastic strain energy in the elastic stage. In the plastic stage, the elastic strain energy density in the plastic zone reaches the storage limit, which is reduced due to the strain-softening behaviour. Thus the dissipated and released energy of the surrounding rock increases exponentially. For deep rocks with high peak strength, the energy evolution in the plastic stage is dominated by energy release, which indicates that rockburst mainly results from the energy release mechanism. In contrast, for the surrounding rock with low strength, the energy evolution during excavation unloading is dominated by energy dissipation due to the significant strain softening behaviour. Large squeezing deformation mainly stems from the energy dissipation mechanism.