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| Failure characteristics of surrounding rock and parameter optimization for tunnel arch foot blasting using arch cover method |
| WANG Haoyun，ZHANG Wanzhi，ZHANG Heng，SUN Yanfeng，YUAN Mingzhan
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(1. School of Architecture and Civil Engineering, Xihua University, Chengdu 610039, Sichuan, China；
2. School of Qilu Transportation, Shandong University, Jinan 250002, Shandong, China；
3. Jinan Mingen Intelligent Technology Co., Ltd., Jinan 250023, Shandong, China)
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Abstract To address severe overbreak and excessive rock mass damage induced by blasting excavation at tunnel arch foot regions, a comprehensive investigation was conducted using the arch-cover method employed in Qingdao Metro Line 6 station as the engineering case study. Numerical simulations were integrated with field experiments to optimize blast hole layout and charging parameters for arch foot excavation. The propagation and coalescence mechanisms of blast-induced fractures in the arch foot rock mass were systematically examined, along with detailed characterization of damage characteristics. A novel nested long-short hole arrangement technique was subsequently developed. The results indicated that the implementation of long-short hole blasting generated dense, interconnected fracture networks around the blast holes, which effectively facilitated the formation of the excavation contour. Compared to conventional perimeter hole arrangements, a significant reduction in damage zones was observed on both the free surface side and the deep surrounding rock side, with maximum decreases of 19.4% and 29.2%, respectively. Upon application of the optimized arch foot blasting parameters, a smooth excavation profile was achieved, characterized by minimized overbreak and eliminated underbreak. Furthermore, the maximum overbreak value was reduced by 59.4% compared to pre-optimized blasting, leading to substantial improvements in both blasting efficiency and excavation quality.
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Received: 16 April 2025
Published: 17 August 2025
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