Abstract: The authors establish a theoretical model for the mechanical response of advance long-pipe roofs, considering the influence of pipe roof overlap and support conditions at both ends. Using the finite difference principle, a calculation method for deflection at various pipe roof positions is developed. The model examines the influence of pipe roof diameter, excavation spacing, and pipe roof overlap on deflection changes. Furthermore, a case study on the Haicang tunnel in the Xiamen Second West Passage is conducted to optimize its reasonable excavation spacing. The results indicate the following: (1) The maximum error of the proposed model is only 8.14% compared to the field test results, and pipe roof overlap eliminates the unreasonable upward arching of deflection. (2) Increasing the pipe roof diameter gradually decreases the maximum deflection, but the reduction effect weakens. (3) At an excavation spacing of 1.2 m in the Haicang tunnel, the crown deflection is reduced by 67.35% compared to that without a pipe roof, and the maximum principal stress of the primary support is adjusted to a more uniform state.

Key words: tunnel engineering, advance long-pipe roof, spatial effect of load, bearing mechanism of pipe roof, engineering application