A Novel Dynamic Fractional Mechanical Model for Rock Fracture Under True Triaxial Static-Dynamic Combined Loading and its Engineering Application.

The frequent far-field microdynamic disturbance caused by excavation of high-stress deep underground engineering will induce the continuous damage deterioration of surrounding rock and ultimately lead to disasters, however, the disturbance deformation and damage evolutions under true triaxial static-dynamic combined loading are unclear, and corresponding mechanical model characterizing these properties are scarce. Therefore, this study carried out a series of true triaxial static-dynamic combined loading tests to study the microdynamic disturbance characteristics of rock. The equal cyclic curve method is proposed to determine the defined disturbance critical stress of rock entering the acceleration stage. The separation methods of true triaxial static induced damage and microdynamic induced damage are proposed, and their evolution laws were investigated and the corresponding damage models were established. Further, a damage fractional mechanical model of rock was established, and the theoretical prediction curves were in reasonable agreement with the experimental results. Sensitivity analysis of static-dynamic combined stress and model parameters on disturbance deformation behaviors were further investigated, and model prediction research for the untesting conditions was also carried out to provide more understanding basis for the surrounding rock disaster mechanism and stability analysis of deep engineering under microdynamic disturbance. Numerical simulation of excavation response for typical deep buried engineering was carried out with the proposed mechanical model. Then a rock disturbance fracture degree index was proposed to realize the quantitative characterization of the location, morphology, and degree of disturbance failure in deep buried engineering surrounding rock, and found that disturbance loads promote the further expansion of the plastic zone in the surrounding rock after excavation, inducing further damage to failure. Highlights: A test method for separating true triaxial static damage and disturbance damage was proposed. The threshold of rock entering the deformation acceleration stage was defined and calculated. A novel microdynamic damage fraction mechanical model was proposed, which can well characterize the experimental results. Sensitivity analysis of static and dynamic stresses and model parameters were investigated. A rock disturbance fracture degree index was proposed to evaluate disturbance failure degree of surrounding rock after excavation. [ABSTRACT FROM AUTHOR]