Theoretical and numerical investigation of damage zones in deep tunnels within a layered rock mass under full-face blasting

The spatial characteristics and mechanism of formation of a blast-induced damage zone (BIDZ) in tunnels with layered rock mass are not well understood, despite being a common excavation phenomenon. Layers affect how stress waves propagate and lead to the formation of a BIDZ. Theoretical analysis and numerical simulation were conducted to investigate the propagation of blast stress waves and the spatial distribution of the BIDZ. From a theoretical perspective, the propagation process of blasting stress waves and the damage depths in the layered rock mass were calculated. Dynamic modelling results show that the proposed blasting damage model incorporating tensile and compressive-shear coupling with equivalent boundary methods, captures the three-dimensional patterns of the BIDZ. The spatial characteristics of the maximum and minimum damage depths were at the roof and foot of the tunnel, as evinced by in-situ tests. Furthermore, this study offers critical insights for predicting damage and vibration effects by comparing with four widely used models. The maximum damage depth is affected by the thickness and dip angle of the layer, as well as the in-situ stress. Both the spatial extent and radial depth of the BIDZ exhibit a positive correlation with the thickness of the layers. The dip angle of rock layer affects the location of the maximum depth of damage in the tunnel section. The findings highlight how important it is to account for the BIDZ when assessing the safety and stability of a tunnel within a layered rock mass, as well as optimizing any support design.