Abstract: In an attempt to investigate the energy variation properties of gneiss under different initial fracture states, uniaxial and triaxial tests were designed and conducted on rock specimens from a tunnel project. By analyzing the stress-strain curves of test specimens, the evolution of energy with strain was obtained. Results show that in-situ stress environment has great influence on the properties of rock specimens. The energy evolution rule of gneiss can be divided into three stages in triaxial test: secondary steady growth stage, stable fracture stage, and accelerated fracture stage. Gneiss of high damage degree is of weak ability to restore elastic energy.The expansion of gneiss is more obvious and fracture occurs at more positions. Fractured compacted rock stores higher proportion of elastic energy, with more apparent brittle failure. If the practical energy release rate is higher than theoretical elastic energy release rate under confining pressure unloading, damage will be produced to weaken the strength of rock.This study enriches the cognition of energy evolution of damaged rock mass and provides a new idea for the construction in gneiss engineering.

Key words: gneiss, elastic energy, energy dissipation, uniaxial test, triaxial test, damage degree