Analysis of the Load Bearing Mechanism and Mechanical Properties of the Advanced Pipe Roof and Discussion on Its Engineering Application

To understand the load bearing and deformation characteristics of the pipe roof and optimize the support scheme, ensuring the safe construction of tunnels in poor geological conditions, this paper discusses the role of advanced pipe roof in terms of support mechanisms, environmental influence, and spatial constraint effects. The segmented load bearing characteristics of the pipe roof are revealed. Based on the Pasternak elastic foundation beam theory, a mechanical analysis model for the entire construction process of the pipe roof is established. An analysis of the mechanical characteristics and parameter influences of the pipe roof is conducted using a large-span tunnel project in Fujian as a case study. The results show that grouting to improve the foundation reaction coefficient of rock and soil mass can reduce the deformation of the pipe roof. Increasing excavation round length will cause the pipe roof deformation to increase non-linearly. The pipe roof's diameter, wall thickness, and spacing are significant factors affecting its deformation. The influence of each parameter on pipe roof deformation, from smallest to largest,is as follows: excavation round length, foundation reaction coefficient, pipe roof diameter, spacing, and wall thickness. The optimized design of the pipe roof should consider the compatibility of different parameters, their couplling effects on deformation control, and environmental impact effects.