Creep characteristics and damage mechanisms of rock in the plateau tunnel: Insights from acoustic emission and energy evolution

Abstract

The in-situ stress in plateau tunnels is significantly high and exhibits a complex distribution. Consequently, the long-term creep behavior of deep surrounding rock poses a critical challenge to the stability and integrity of tunnel engineering in plateau mountainous areas. To address this issue, this study performs triaxial creep tests on gneissic granite samples obtained from plateau tunnels under various stress paths. Additionally, the mechanical analysis is enhanced by incorporating acoustic emission characteristics and energy evolution. Two stress paths—continuous loading and confining pressure unloading—were implemented. Key parameters, including AE count, cumulative energy, and energy competition ratio R, were analyzed. The results indicate that: (1) Under the confining pressure unloading path, the accelerated creep stage duration,which just occupied 1.33 % of total loading time, was significantly shorter than that under continuous loading, with a 12.3 % reduction in failure strength, suggesting lower confinement facilitates microcrack propagation and rapid instability; (2) AE parameters and energy release patterns effectively characterized creep stages: steady-state creep exhibited steady AE activity, while abrupt increased in N and ΣE mark accelerated creep, with shear-dominated failure of over 69.9 %; (3) The energy competition ratio R grew exponentially beyond the critical deviatoric stress, though localized energy aggregation still triggered shear failure. This study elucidates how stress paths govern energy distribution and damage evolution, providing theoretical insights for stability assessment and disaster prevention in plateau tunnel engineering.