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Evaluation of a mountain tunnel stability and interaction with new adjacent tunnel construction
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Volume Title: ICASGE2023
DOI: ICASGE-GEO
Authors
Department of Civil and Environmental Engineering,
Faculty of Science and Technology,
Tokushima University,
Tokushima City,
Japan.
Abstract
The New Austrian Tunneling Method (NATM) is a modern tunnel design and construction method which uses advanced monitoring to refine tunnel elements by geological strength.
However, during or after tunnel construction, swelling or squeezing may occur which causes tunnel road surface heaving, especially in non-invert tunnels. The case of study phase 1 is a NATM mountain tunnel, locate in Japan, it was built 28 years ago, with a traffic flow of 30,000 vehicles per day. The tunnel has faced severe invert heave since 2008. To prevent phase 1 from heaving phenomena a reinforced concrete invert will be installed along the non-invert area after the construction of adjacent tunnel phase 2 to keep traffic flow.
Furthermore, excavating a new adjacent tunnel phase 2 becomes a concern since the interaction between tunnels has a significant effect on the surface settlement and current tunnel invert stability.
Therefore, a numerical simulation analysis using FLAC 2D to simulate phases 1 and 2 of the study case is used to predict the surface settlement values, stresses changed regions, and invert displacement deformations that occur during phase 2 tunnel construction.
The methodology is based on the theory of geostress releasing method. The stages of excavation are two, the upper and the lower side. Every stage has three main construction steps excavation, installation of rock bolts, installation of shotcrete lining, then install a second concrete lining. The results showed that there are influences associated with phase 2 excavation on ground surface settlement and phase 1 invert stability.
However, during or after tunnel construction, swelling or squeezing may occur which causes tunnel road surface heaving, especially in non-invert tunnels. The case of study phase 1 is a NATM mountain tunnel, locate in Japan, it was built 28 years ago, with a traffic flow of 30,000 vehicles per day. The tunnel has faced severe invert heave since 2008. To prevent phase 1 from heaving phenomena a reinforced concrete invert will be installed along the non-invert area after the construction of adjacent tunnel phase 2 to keep traffic flow.
Furthermore, excavating a new adjacent tunnel phase 2 becomes a concern since the interaction between tunnels has a significant effect on the surface settlement and current tunnel invert stability.
Therefore, a numerical simulation analysis using FLAC 2D to simulate phases 1 and 2 of the study case is used to predict the surface settlement values, stresses changed regions, and invert displacement deformations that occur during phase 2 tunnel construction.
The methodology is based on the theory of geostress releasing method. The stages of excavation are two, the upper and the lower side. Every stage has three main construction steps excavation, installation of rock bolts, installation of shotcrete lining, then install a second concrete lining. The results showed that there are influences associated with phase 2 excavation on ground surface settlement and phase 1 invert stability.
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