Brittleness of layer sandstone under triaxial loading and unloading

Accurately quantitative characterization of brittleness of coal or rocks is important for effective estimation of excavation efficiency in deep engineering. The in-situ stress evolution characteristics of layer sandstone during the whole life-cycle process must be accompanied by the energy evolution process. Therefore, based on the above energy evolution characteristics, a stress path of three-stage triaxial loading and unloading (TLUT) is proposed. Subsequently, the damage evolution law and brittleness index, BI 16 , are obtained and defined. The results show that: 1) The confining pressure can enhance bearing capacity and plastic deformation resistance of layer sandstone. The loading way and confining pressure have significant influence on the plastic volumetric deformation resistance, but the inclination angle has little influence. 2) The pre-peak damage evolution process under conventional triaxial loading (CTLT) and TLUT can be divided into three stages and the pre-peak damage evolution process under TLUT can be divided into four stages. 3) The whole deformation process of layer sandstone can significantly affect its brittleness, which is dynamic and not constant. It can provide a certain basis for the accurate estimation of excavation efficiency in deep engineering.