Effects of In-situ Stress on Blasting Damage during Deep Tunnel Excavation

The in-situ stress has great influence on blasting damage during deep tunnel excavation. However, the effects of in-situ stress on the blasting damage during tunnel excavation are deficient, and its mechanism is not clear. Therefore, theoretical analyses and numerical simulations are adopted to study the rock excavation damage under the coupling effect of in-situ stress and blasting load. The results indicate that the damage extent has obvious correlation with in-situ stress level. The damage extent decreases first and then increases as the stress level rises. In the decreasing part, blasting load is the dominant factor and mainly causes tensile-shear damage. The rising of in-situ stress here raises the tensile-shear yield limit of surrounding rock, which leads to the reduction of damage extent. When it comes to increasing part, the secondary stress field induced by excavation takes place of blasting load while mainly causing compress-shear damage. The damage extent rises up with the in-situ stress level increasing continuously. For the circular tunnel in this paper, the turning point where the trend of damage extent turns to increasing from decreasing is in-situ stress of 12.5 MPa.