Study on Construction Time of Secondary Lining for Large Section Shallow Buried Tunnel in Soft Rock

摘要

The self-bearing capacity of surrounding rock gets more and more attention on design and construction of tunnel projects nowadays, especially for large section shallow buried tunnel in soft rock. In order to bring it's self-bearing capacity into full play, certain deformation of surrounding rock is allowed when the tunnel has been excavated. But in order to prevent surrounding rock get too large deformation into loose state, and ensure secondary lining play its role in a reasonable range, its construction time must be reasonable. Stable deformation rate of surrounding rock and primary lining has been taken as assessment indicator of construction time of secondary lining in paper. Theoretic solving method of stable deformation rate has been established by regression analysis and numerical analysis of displacement monitoring data, then construction time of secondary lining has been confirmed. Meanwhile we take Hejiazhuang Tunnel as project case to study construction time of secondary lining for large section shallow buried tunnel in soft rock. The research indicates that secondary lining could be constructed when the value of tunnel crown settlement rate is less than 0.49mm/d and the value of sidewall's horizontal absolute convergence rate is less than 0.15mm/d. The result has a certain guiding significance for design and construction of similar projects.