Experimental investigation of contour blasting in anisotropic rocks under different lateral stress coefficients

Abstract

This study aims to analyze the influence of lateral stress coefficient k and anisotropy on the dynamic response and failure characteristics of deep jointed rock masses under contour blasting. Using phyllite as the test material, local contour blasting-unloading experiments are conducted under biaxial conditions. The analysis focuses on the failure characteristics of the tunnel surrounding rock under different k and joint orientations. Results indicate that when k=1, blasting-induced fractures preferentially propagate along the joint direction. As k decreases, these fractures can deviate from the joint direction and extend toward zones of higher local stress. This tendency is particularly evident when the high-stress direction aligns with the tunnel contour, enabling fracture penetration through closely spaced contour blastholes. During the unloading, blasting-induced circumferential fractures undergo further shear failure, while radial fractures are compacted and closed. The failure of tunnel sidewalls is primarily controlled by circumferential stress concentration and anisotropic compressive strength, whereas failure at the tunnel crown is mainly governed by blasting stresses and the anisotropic tensile strength of the rock mass. This study proposes conditions for the initiation and coalescence of blasting-induced fractures, providing a theoretical basis for contour blasting and support design in anisotropic rock masses.

Keywords

laboratory experiment / contour blasting / excavation unloading / failure characteristics / lateral stress coefficient / anisotropic rocks

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Central South University