Amidst the rapid expansion of China's railway network,the construction of new shallow tunnels that cross beneath existing operational railway lines is increasingly common,posing significant threats to the safety of both tunnel construction and railway operations.Based on the construction of a railway tunnel,this study introduced a novel"short cycle,three-stage lining with pile cutting"approach.Through the examination of lining structure calculations,three-dimensional numerical simulations,and practical applications,the following conclusions are drawn:(1)In ultra-shallow tunneling projects involving small-angle crossings beneath operational railways,this methodology enables flexible assembly of D-type temporary supports,overcoming limitations imposed by fixed D-type beam lengths.(2)The three-stage lining not only enhances the safety factor of the permanent support structure but also addresses waterproofing concerns.The minimum safety factors for the secondary and tertiary linings,respectively located in the arch crown,are found to be 5.8 and 14.9,both meeting regulatory requirements.(3)Excavation progresses from both ends towards the middle,resulting in a"Λ"shaped profile of initial lining vault settlement,with the smallest settlements occurring in the final 8 m stretch before breakthrough.(4)Undertaking pile cutting after the secondary lining reaches 100%design strength mitigates tunnel vault settlement caused by changes in pile support points.(5)The method effectively manages stress release through short excavation cycles and prompt support installation,thereby minimizing ground settlement-induced railway track deformation due to ground loss.A five-year follow-up investigation reveals no instances of lining cracks or water ingress,substantiating the safety and feasibility of the proposed methodology.
shallow tunnelcrossing beneath railwaysnovel construction methodnumerical analysispractical application
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