Abstract: With the expressway construction going into the mountain areas, the number of tunnels as structures are increasing due to the restriction of the highway alignments, the landform, the environmental protection requirements, the water sources and other factors. From many years of tunnel construction and operation practice experience, lining cracks are one of the most common major hazards. Effectively prevent and mitigate the lining cracking are the key technical problem related to the safety of the tunnel construction and operation. Based on a case history of the secondary lining cracking at the top of an expressway tunnel, this paper evaluates the distribution characteristics of cracks in the lining system, the patterns of these cracks and the deformation in the secondary lining of the tunnel by means of tunnel monitoring and measurement. On this basis, factors that inducing cracks are analyzed, and mitigation measures such as reinforcing the bottom, adding drainage pipe, and installing steel plate in the secondary lining reinforcement are proposed, which have achieved satisfactory results and also provide a reference for the mitigations of similar projects.

Key words: Tunnel Engineering, Secondary Lining Cracking, Monitoring and Measurement, Hazard Evaluation, Cracking Mitigation