Research on Inadequate Lining Thickness and Dehollowing Hazards and Remediation in the Vault Area of Operational Tunnels

Inadequate lining thickness and debonding are very common in operating tunnel vaults, which may cause local cracking and falling blocks in the lining and threaten tunnel operation safety if not rectified in time. By means of data research, numerical calculation and field application, the hazards of such defects and their remediation measures were studied. The study shows that: the severity of insufficient lining thickness and debonding is graded by 2.0 m and 6.0 m in longitudinal and circular directions; When the lining defect range is small, the lining thickness change has less effect on the lining stress. When the lining defect range is larger than 4 m² and the lining thickness is less than 40% of the design thickness, it will cause sudden change of lining stress; When the single size of defects in longitudinal and circular directions is larger than 2 m, the circular dimension is more likely than the longitudinal. When the longitudinal and circumferential single size of defects is larger than 2 m, the circumferential size is more likely to cause the change of lining stress than the longitudinal size; Combined with the grading of lining defects and lining thickness, three remediation schemes of filling and grouting, window repair and lining set are proposed; Based on the actual application of the project, the correctness of the grading of defects and the feasibility and effectiveness of the remediation scheme are verified, which can provide some guidance and reference for the remediation of insufficient tunnel lining thickness and dehollowing.