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The self-stability of fly ash accumulation body is poor, and it is broken into scattered particles after stress. When the tunnel passes through the fly ash field, the unstable surrounding rock poses a great threat to the construction safety. Based on the double- arch tunnel of Yanpingba, the plastic-hardening constitutive model was selected according to the comparison of mechanical properties of fly ash. The finite difference software FLAC3D was used to simulate the construction of different excavation offsets. The influence of different excavation stagger distances of 5, 10, 15 m on the surrounding rock and structure of double-arch tunnel in fly ash accumulation stratum was studied. The results show that the step excavation offset of the pilot tunnel should not exceed 10 m, and the maximum stress of the 15 m offset condition increases by 36. 82% compared with that of the 10 m offset condition. The small excavation offset of the left and right tunnels can effectively reduce the displacement of the arch top of the pilot tunnel. After the completion of the excavation of the middle pilot tunnel, the vertical displacement of the left and right vaults has reached about 50% of the total settlement. The settlement displacement of the left tunnel vault increases approximately linearly with the excavation offset, and the excavation of the subsequent tunnel has a greater impact on the first tunnel. The stress concentration area was distributed in different positions when the main tunnels was excavated with different offsets. The stress increment of the structure increased rapidly after 10 m offset, and the maximum stress of 15 m offset increased by 17. 28% compared with 10 m offset. The excavation distance of the main tunnel should not exceed 10 m. [ABSTRACT FROM AUTHOR]

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Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)