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This paper attempts to make an accurate assessment of the safety and stability of tunnels in blasting excavation, considering the effect of rock mass intactness. For this purpose, numerical simulations and field tests of tunnel blasting excavations were carried out in rocks with different intactness indexes. For simplicity, the multi-hole blasting load was replaced with the equivalent blasting load according to the Chapman-Jouguet (C-J) detonation mechanism and the theory of stress wave propagation in elastic medium. Then, the existing blasting damage model of rock mass was improved into a continuum damage model of rock blasting considering the intactness of rock mass, and imported to FLAC3D for numerical simulations of tunnel blasting excavation. The simulation results were then verified through field tests on blasting vibration velocity and acoustic wave velocity. The attenuation law of blasting vibration was obtained from the tests on blasting vibration velocity, while the blasting-induced fracture zone was determined through the tests on acoustic wave velocity in the borehole before and after blasting. The blasting-induced fracture zone near the explosion sources and the attenuation law of blasting vibration velocity far from the sources were both identified in the numerical simulations and the field tests. After that, the results of the numerical simulations were compared with those of the field tests. The comparison shows that: after the blasting excavation of pressure diversion tunnels, the maximum and the minimum depths of blasting-induced fracture in the surrounding rock respectively appeared at the haunch and the vault of tunnels; when the drilling and blasting parameters remained constant, the maximum depth of blasting-induced fracture and several other factors decreased significantly with the growth of the intactness index; meanwhile, the vibration-influenced distance of blasting increased first and then decreased. The results of numerical simulations agree well with those of the field tests. The research findings provide valuable guidance to blasting excavation of pressure diversion tunnels
hydropower plant; pressure diversion tunnel, numerical simulation, the intactness index, blasting vibration velocity, acoustic wave velocity
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