Blasting crack propagation patterns and parameters optimization in tunnel with layered jointed rock mass

During tunnel construction using the drilling and blasting method, layered jointed rock masses often pose engineering challenges such as over- and under-excavation of the crown and working face. The authors addressed these challenges via theoretical analysis, numerical simulation and field testing. Theoretical analysis revealed that blasting energy utilization is maximized when the jointed structural plane is perpendicular to the fracture control plane. The numerical simulation results shown that that layered joints significantly block and interfere with the propagation of explosive stress waves, reducing the transmission of explosive energy within the rock mass. They govern and direct the expansion of blast-induced cracks, inducing deviation and bifurcation. On site blasting tests have shown that setting empty holes between blast holes could govern and direct the expansion direction of cracks between blast holes, thereby suppressing large-scale collapse of the rock mass at the crown and spandrel, and avoiding over- and under-excavation at the working face. On this basis this study optimized tunnel blasting parameters and the layout scheme of surrounding holes, and provided robust technical support for the precise control of tunnel excavation in layered jointed rock masses.