Coupling Effect of In Situ Stress and Blasting Load on the Influence Range of Grouted Rock

Strong blasting disturbance caused by blasting load and high in situ stress is a key problem for weak and broken rock excavation in underground tunnels. Advanced grouting can help control rock blasting damage. However, the effect of in situ stress on grouted rock damage is unclear, which may increase the difficulty of subsequent blasting design and support. This study investigates the influence range of grouted rock under the coupled effect of blasting load and in situ stress using both theoretical and numerical methods. The propagation characteristics of blasting stress waves in the near field of the blasting source and the redistribution law of in situ stress are first presented to investigate stress changes during blasting excavation of grouted rock. A model to calculate the safety velocity (SV) is then proposed to study the effects of the lateral pressure coefficient and magnitude of in situ stress on grouted rock. The blasting influence range can be inferred from SV and peak particle velocity. Finally, a numerical model of an underground tunnel was built to analyze the blasting influence range of grouted rock under different in situ stress conditions. The results indicate that in situ stress redistribution causes initial shear damage and that the range increases with increasing in situ stress magnitude. The distribution characteristics of in situ stress have a guiding effect on the blasting influence range, which is larger in the direction perpendicular to the maximum in situ stress. SV is the smallest when the lateral pressure coefficient is 2 and the polar angle is 55°. Thus, both the magnitude and the lateral pressure coefficient should be considered in blasting design for advanced consolidation grouting of rock.