Abstract
The bench method exhibits significant advantages in saving construction time and improving mechanized operation levels, but has certain limitations in controlling surrounding rock stability and preventing deformation. To reduce the deformation impact of bench excavation on tunnel surrounding rock, the rapid excavation technology of the micro-bench method for cold-region tunnels is elaborated based on the Chongli Tunnel project; and through finite element simulation, the bench length and height during bench method construction are optimized to determine the bench parameters for single-track railway tunnel surrounding rock. The results show that during micro-bench method construction, the working procedures of each working area at the tunnel face are carried out simultaneously and independently without mutual interference, effectively improving construction speed; for Grade IV surrounding rock, an upper bench height of 4m is more appropriate, resulting in relatively small crown settlement and peripheral convergence while tunnel face extrusion deformation remains within the control range; increasing bench length can maintain tunnel face stability but will increase crown settlement and peripheral convergence, therefore longer is not necessarily better for the upper bench length, and the length of the upper bench for Grade IV surrounding rock should be controlled at 3m.
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Preamble
Study on Rapid Excavation by Micro-Step Method and Step Parameters Optimization in Cold-Region Tunnels
ZHANG Shengli
China Railway 16th Bureau Group Fourth Engineering CO., Ltd., Beijing 101400, China
Abstract
The step method demonstrates significant advantages in reducing construction time and enhancing mechanized operation levels, yet exhibits certain limitations in controlling surrounding rock stability and preventing deformation. To minimize the deformation impact of step-method excavation on tunnel surrounding rock, this study employs the Chongli Tunnel project as a case study to elaborate on rapid excavation techniques using the micro-step method in cold-region tunnels. Through finite element simulation, the step length and height during construction are optimized to determine appropriate step parameters for single-track railway tunnel surrounding rock.
The results indicate that during micro-step method construction, various working zones at the tunnel face operate simultaneously and independently without mutual interference, effectively improving construction speed. For Grade IV surrounding rock, an upper step height of 4 m is most suitable, yielding relatively small crown settlement and peripheral convergence while keeping face extrusion deformation within controllable limits. While increasing step length helps maintain tunnel face stability, it also increases crown settlement and peripheral convergence, indicating that longer upper steps are not necessarily better. Therefore, the upper step length for Grade IV surrounding rock should be controlled at approximately 3 m.
Keywords: cold-region tunnels; micro-step method; surrounding rock deformation; parameter optimization