Uniaxial compression creep and acoustic emission characteristics of sandstone under loading-unloading paths

Specimens of red sandstone are subjected to creep and acoustic emission (AE) tests under only multi-level loading and multi-level loading-unloading. Creep deformation characteristics and AE parameters of the red sandstone specimens under these two loading paths are compared and analyzed, and a creep AE damage-variable model is used for the damage evolution of the micro-cracked structures inside the rock during the creep process. The research results reveal the following: (1) During the creep process involving multi-level loading-unloading, the temporal variation of the AE amplitude is similar to that observed during the creep process involving only multi-level loading. (2) The variations of the cumulative AE event and cumulative AE ring-down count in the creep process involving multi-level loading-unloading are similar to those in the creep process involving only multi-level loading, while the actual values are higher in the former process. (3) The creep AE damage-variable model performs well on characterizing the damage evolution of the internal micro-crack structure of the rock in both creep processes.