Construction Methods of Longitudinal Synchronous Grouting for Tunnel Crown Secondary Lining Voids
Conventional void prevention technologies for the crown of secondary tunnel linings struggle to signifi-cantly reduce void formation and often result in layering between cast-in-place concrete and grouts.To address these issues,a study was conducted based on the Qu'ao Tunnel on the Lanzhou-Hezuo Railway.Using numerical simulation,the impact of crown voids and asynchronous grouting on the stress behaviors of the lining structure was analyzed.A longitudinal synchronous grouting technology for the crown of secondary linings was proposed,and its effectiveness was verified through field applications and cross-detection using various specifications of ground-pene-trating radar.The findings are as follows:(1)Compared to a dense state,crown voids and asynchronous grouting in-crease the minimum principal stress of the crown by 86%and 39%,respectively.This indicates that crown voids pose the greatest safety risk to secondary linings,and layering between grouts and concrete is also a weak point in the structure.Grouting must be synchronized with concrete casting to ensure the integrity of secondary lining;(2)The proposed longitudinal synchronous grouting technology involves arranging grouting pipes with vent openings along the longitudinal direction within the inner edge of the waterproof board at the crown.Grouting is performed im-mediately after concrete placement and compaction,eliminating blind spots in radial grouting and avoiding cavities or density defects.This also eliminates the composite beam effect in the lining structure and enhances its overall load-bearing capacity;(3)The construction method for longitudinal synchronous grouting is simple to operate and significantly reduces costs compared to radial grouting with mold.
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