Dynamic response and failure characteristics of surrounding rock in existing tunnel under transient excavation of adjacent tunnel

In deep rock engineering, the instability of surrounding rock induced by transient excavation of adjacent tunnels significantly compromises engineering safety, with dynamic disturbances from drill-and-blast methods being particularly remarkable. Existing laboratory tests fail to accurately simulate the transient unloading process during tunnel excavation, leading to insufficient understanding of the dynamic response and failure mechanisms of existing tunnels. This study employs a novel experimental system for transient unloading during tunnel excavation, which effectively replicates the stress path and unloading rate during transient excavation. Using hard-brittle rock-like material specimens, the dynamic response characteristics of existing tunnels under adjacent tunnel excavation were investigated with varying clear distances ( D ) and lateral pressure coefficients ( k 0 ). Digital Image Correlation (DIC) technology was utilized to analyze strain evolution in thin-plate specimens under biaxial static loading, while systematically comparing the strength and failure characteristics under two loading modes: biaxial static loading and biaxial loading-unloading-overloading. Based on mesoscopic damage criteria, damage types in the surrounding rock of existing tunnels after adjacent tunnel unloading were identified. Results demonstrate that compressive-shear failure predominates at larger tunnel clear distances, while tensile and tensile-shear failures primarily occur at smaller clear distances.