Stress interaction and crack penetration mechanism between smooth blasting holes for tunnel excavation under high in-situ stress
FAN Yong1，2，SUN Jinshan1，3，JIA Yongsheng1，3，YAO Yingkang1，3，ZHANG Zhen1，3，DU Yuxiang1，3
(1. Hubei Key Laboratory of Blasting Engineering，Jianghan University，Wuhan，Hubei 430056，China；2. Hubei Key Laboratory of Construction and Management in Hydropower Engineering，China Three Gorges University，Yichang，Hubei 443002，China；3. State Key Laboratory of Precision Blasting Engineering，Jianghan University，Wuhan，Hubei 430056，China)
Abstract：At first，for the smooth blasting of tunnel under high in-situ stress，the stress field between smooth holes induced by blasting was calculated by using the cylindrical cavity excitation model，and the influence of in-situ stress on the superposition of blasting stress between holes was analyzed. Then，the verified RHT numerical model was employed to simulate the circumferential tensile stress field induced by blasting under the conditions of single hole，double holes，three holes and in-situ stress，and the effect of radial uncoupling coefficient，hole spacing and in-situ stress on the cracking characteristic between smooth blasting holes was studied. Finally，some suggestions on the selection of smooth blasting parameters considering the influence of in-situ stress were given，and an application in blasting excavation of diversion tunnel at Jinping II hydropower station was presented. The results indicate that the superposition of blasting stress waves leads to the increase of the circumferential tensile stress near the midpoint of the line between smooth blasting holes，showing the characteristic of peak shaped bulge，while the radial compressive stress produced by the redistribution of in-situ stress is opposite to the action direction of the circumferential tensile stress induced by blasting between smooth holes，which will inhibit the crack formation and penetration between smooth holes；Influenced by in-situ stress，the propagation of blasting cracks shows obvious directionality and tends to expand along the direction of the maximum principal stress. Therefore，for the general smooth blasting design with the hole diameter of 42 mm，the charge diameter of 32 mm，the smooth blasting layer thickness of 0.6 m，when the in-situ stress increases from 20 MPa to 40 MPa，the hole spacing should be reduced from 0.75 m to 0.60 m，and the holes should be arranged along the direction of the maximum principal stress to ensure the formation of cracks between holes and shaping of excavation wall.
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2023, Vol. 42 
