Application of Displacement Direction Angle Theory on Excavation Methods Conversion Opportunity of Zi-Zhi Tunnel
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Stratum in shallow buried excavation section of Zi-Zhi Tunnel is generally upper-soft and lower-hard. To reduce the rock disturbance and ensure the construction progress, excavation method conversion from Cross Diaphragm with Step method to bench method should be conducted ahead of schedule. To determine the excavation methods conversion opportunity, considering different positions between tunnel face and the interface of stratum, based on displacement direction angle theory, the change laws for the displacement direction angle and three-dimensional deformation of surrounding rock under different conditions were analyzed by FLAC3D. Then, an excavation methods conversion opportunity is derived. Meanwhile, the rationality of the opportunity is validated by the field monitoring data. The results indicate that: when the distance of working face cutting through the interface is 1.5B (B = tunnel width), displacement direction angle of surrounding rock reaches a stable state and the longitudinal stress concentration is weakened. It is conducive to utilize the self-bearing capacity of the rock mass. Hence, it is suggested to convert the excavation methods when the distance is greater than 1.5B; the stable value and the convergence rate of vault subsidence in site were both below warning value, which can meet the safety and economic benefits of engineering.
KeywordsShallow-buried tunnel Displacement direction angle Upper-soft and lower-hard Excavation methods conversion
The authors appreciate the support of Science and Technology Plan Projects of Hunan Province, China (2010GK3173) and co-sponsored by the China Railway Tunnel Group Science and Technology Innovation Project (2013–30).
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