Abstract: To solve the service life reduction and operation safety risks induced by structural cracks in the composite lining of a highway tunnel, this paper presents the typical geological section of Yangling Tunnel in Yixing as a case history and evaluates the influence mechanism of the geological conditions of surrounding rock mass, construction methods and the concrete material on the structural cracks in the secondary lining. The results indicate that, (1) the premature form work removal resulted in insufficient early strength of the secondary lining of the concrete, which led to hidden cracks in its interior under the action of dead weight stress and the surrounding rock compressive stress; (2) the stress concentration at the end of the crack induced by the temperature gradient stress induced by the under-curing of concrete led to the growth and the coalescence of the hidden cracks inside. In the view of the cracks with different opening degrees, the corresponding grouting reinforcement treatment measures are proposed to improve the strength and the integrity of the lining structure and effectively ensuring the safety of the surrounding rock mass and the maintenance structure during the operation of the tunnel.

Key words: highway tunnel, structural cracks, stability analysis, mitigation measures