Blasting excavation method and parametric tests for tunnel arch crossing shale

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Journal of Vibration and Shock ›› 2022, Vol. 41 ›› Issue (15) : 90-98.

ZHANG Wanzhi1, 2, XU Bangshu2, GE Yanhui1, MEI Jie2, ZHU Yongxue3, WANG Bingkun3

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Abstract

When the arch of tunnel passes through shale, the characteristic of surrounding rocks are upper soft and lower hard. In this case, the blasting excavation leads to problems of the arch rock falling and collapse. Based on the Hailuoyu tunnel project, the blasting excavation test and numerical simulation method were applied to analyze the damage characteristics of arch shale, and the upper bench CD method of tunnel in upper soft and lower hard rock mass was proposed. Then, some optimization measures were put forward, such as blasthole pattern and charge parameters of smooth blasting rock layer, cutting hole layout and its maximum single hole charge. By comparing and analyzing the danage characteristics, overbreak and deformations of surrounding rock during tunnel excavation, it was found that the optimized blasting excavation method has better quality of surrounding rock contour formation. The results show that when the tunnel arch passes through shale, the roof shale is easy to be broken layer by layer from bottom to top along the structural surfaces, and the shale from spandrel to haunch tends to open and fracture along the structural surfaces. The upper bench CD method is beneficial to reduce the one-off excavation area and restrain the separation of shale. Simultaneously, the damage of surrounding rock can be reduced by using optimized blasting parameters, and the side length of irregular broken profile is reduced from 0.9 m to 0.4 m. The maximum linear overbreak and average overbreak area of tunnel after optimization is greatly reduced, which is shown as: the maximum linear overbreak at vault is decreased from 100.2 cm to 28.6 cm, at spandrel is reduced from 50.1 cm to 20.1 cm, and the average overbreak area is reduced by 48.2%. Simultaneously, the cumulative deformation of surrounding rock is reduced, the maximum settlements of left and right pilot heading are decreased by 47.8% and 34.9% respectively, and the horizontal convergence of arch waist is reduced by 33.3%. The vault settlement increases of left and right pilot heading of the upper face arch are decreased by 7.6% and 6.2% respectively, while the arch waist horizontal convergence is decreased by 3.1% after the excavation of the lower face.
Key words：large cross-section tunnel; shale; blasting excavation; overbreak; optimization of blasting parameters

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large cross-section tunnel / shale / blasting excavation / overbreak / optimization of blasting parameters

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ZHANG Wanzhi1, 2, XU Bangshu2, GE Yanhui1, MEI Jie2, ZHU Yongxue3, WANG Bingkun3. Blasting excavation method and parametric tests for tunnel arch crossing shale[J]. Journal of Vibration and Shock, 2022, 41(15): 90-98

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