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By integrating an established rock damage model into the LS-DYNA computer code and using a widely used method for equivalently simulating multiple blastholes detonation, the damage processes of surrounding rock with different properties under the bench blasting of a large cross-section tunnel are comparatively studied. The damage distribution across the excavation cross-section is characterized by greater damage at the upper and lower ends, with lesser damage in the middle (junction between adjacent benches). For grade III surrounding rock excavated with two-bench blasting, the maximum damage depth of 3.6 m occurs in the middle floor. For grades IV and V surrounding rock excavated with three-bench blasting, the maximum damage depths both occur at the vault, with 3.6 m and 2.5 m, respectively. In bench blasting, the blasting of breaking holes closest to the excavation boundary significantly impacts surrounding rock, whereas the damage caused by smooth holes blasting is minor. The surrounding rock with poorer mechanical properties tends to exhibit greater damage under the same blasting operations. According to the proposed method, the critical Peak Particle Velocity (PPV) for cumulative damage in grades III, IV, and V surrounding rock of the Longnan tunnel is 16.8 cm/s, 13.7 cm/s, and 11.5 cm/s, respectively. [ABSTRACT FROM AUTHOR]

Drilling and blasting method used for excavation causes damage to surrounding rock mass, and frequent blasting often leads to cumulative damage effects. Thus, understanding the distribution of Blast-Induced Damage (BID) zone is critical to assess the slope stability of open-pit mines. Herein, this study aims to investigate the cumulative damage effects and safety control criteria on the final wall of the open-pit slope under blasting. The cumulative damage zone was defined using a continuous damage model coupled with tensile damage and Drucker–Prager yield criteria embedded in the finite difference method. The simulation results were validated against field data collected from the Wushan open-pit mine in Inner Mongolia, China. The results demonstrate that the cumulative damage of the final wall exhibited a non-linear decreasing trend from the bench face to the interior of the slope, successfully reproducing the spatial distribution of the BID obtained from the in situ test, and revealing that the maximum cumulative damage depth occurred at the slope crest. Additionally, a safety control criterion for the critical damage zone of open-pit final slope was proposed based on the investigation of the effects of dynamic loading rate and stemming length on excessive overbreak. The results highlight how important it is to account for cumulative damage effects when assessing the final slope stability of an open pit and optimizing the mining design. Highlights: The cumulative damage effects on the final wall of the open-pit under blasting are investigated. A model coupled with tensile damage and Drucker-Prager yield criteria is established and incorporated into finite difference method to simulate the blast-induced damage zone. The subsurface damage depth is obtained using the digital drilling images technology. The dynamic loading rate and stemming length could significantly affect the excessive overbreak along the crest. [ABSTRACT FROM AUTHOR]

The cumulative damage effects of surrounding rock under single full-face blasting and multiple full-face blasting of a large cross-section tunnel are comparatively studied in this paper. The damage processes of the single and multiple full-face blasting of the tunnel are simulated by the established rock damage model embedded into the LS-DYNA computer code through its user subroutines and a cumulative damage simulation technology in the LS-DYNA. The simulation results are verified against field test data. The results demonstrate that the numerically predicted peak particle velocity (PPV) of the surrounding rock under multiple full-face blasting is more consistent with field test data than that under single full-face blasting, which indicates the advantages of multiple full-face blasting in comparison to single full-face blasting in simulating the blasting process of a tunnel. The maximum damage depth in the middle of the tunnel invert is mostly affected by multiple full-face blasting. Both the maximum damage depth and the maximum PPV occur in the middle of the tunnel invert under single and multiple full-face blasting. Based on the defined damage threshold Dcr and the modeled maximum damage depth of the surrounding rock, the influence of initiation sequence on the critical PPV for rock damage is analyzed, and a critical PPV of rock damage is proposed to provide a safety criterion for tunnel blasting excavation. [ABSTRACT FROM AUTHOR]

A blast-induced damage model integrating the tensile damage model with the Drucker-Prager yield condition is established. Based on the excavation of a large cross-section tunnel in China, the damage process of surrounding rock under multiple full-face blasting is simulated by the established rock damage model embedded into the LS-DYNA computer code through its user subroutines and a cumulative damage formulation in the LS-DYNA. The simulation results are well verified against field test data. The results show that the maximum damage depth of surrounding rock is determined by the blasting of the excavated cross-sections closest to the surrounding rock. Both the maximum damage depth and the maximum peak particle velocity (PPV) occur in the middle of the tunnel invert. Based on the defined damage threshold D cr and the modeled maximum damage depth of surrounding rock, the influence of initiation sequence on the critical PPV for rock damage is studied, and a critical PPV associated with rock damage is proposed for tunnel blasting excavation. [ABSTRACT FROM AUTHOR]