Abstract
Collapse of the vault and numerous other safety accidents often occur during the construction process of large-section tunnels. The utilization of a small pilot tunnel and a step reverse expansion construction methodology is proposed based on conventional construction methods to explore safe construction technology. First, a theoretical analysis combined with on-site monitoring parameters was conducted. It showed that the maximum displacement of the tunnel surrounding rock was 0.027 m during the elastic stage and increased to 0.031 m during the strength limit stage. The overall surrounding rock deformation does not have a noticeable impact on tunnel safety. A numerical simulation model of the small pilot tunnel advancement and step reverse expansion method was established. Simulation results showed that the first two excavation steps caused 89.6% of the total overlining strata subsidence, and the use of a small pilot tunnel advancement and step reverse expansion method can enhance the tunnel support. The tunnel surrounding rock was adequately stabilized after using this excavation method and provides the in-situ conditions for expanding the pilot tunnel to the large-section tunnel. The proposed method was adopted in an actual engineering project. It protected the subsequent construction of the main tunnel and decreased construction time, saving construction costs while ensuring safety, reducing construction risks, and improving production efficiency. This research can guide similar tunneling projects.
Highlights
With the rapid development of the global social economy and logistics, traditional small-section tunnels are no longer suitable for the increasing traffic
Based on summarizing traditional methods, we developed a new excavation method. e adopted excavation and supporting method have achieved excellent engineering and economic benefits. is research provides a guideline for similar tunneling engineering
When the tunnel surrounding rock is at its strength limit, the radius of the plastic zone is 2.67 m, the displacement at the outer boundary of the plastic zone is 0.031 m, the maximum displacement around the tunnel is 0.008 m, and the overall reduction of the tunnel section is about 0.5 m2, which accounts for 0.1% of the total area. e overall deformation is minimal and does not affect the normal production of tunneling
Summary
With the rapid development of the global social economy and logistics, traditional small-section tunnels are no longer suitable for the increasing traffic. Numerous studies have been conducted on the mechanical properties and excavation methods of surrounding rock. Li and Kang [25] summarized several problems in constructing large-section tunnels and compared the advantages and disadvantages of different excavation methods. E stability of tunnel surrounding rock is directly related to the physical and mechanical properties of the rock, geological environment, tunnel excavation method, construction sequence, excavation rate, amongst other parameters. Differing from the conventional tunnel support method, a small pilot tunnel and step reverse expansion provide information on the in-situ conditions for the construction of the main tunnel. Is paper took a super-large cross section tunnel as an engineering example, comprehensively analyzed the environment of the tunnel, and explored suitable methods for excavation. Based on summarizing traditional methods, we developed a new excavation method. e adopted excavation and supporting method have achieved excellent engineering and economic benefits. is research provides a guideline for similar tunneling engineering
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