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Under the combined impacts of the operation time, design concept, and construction technology, extensive damage has occurred in tunnels built in China during the early stages of rapid development. Therefore, relevant research on tunnel damage is of urgent importance. This study takes the Liupanshan Highway Tunnel on G312 in Guyuan City as a case study, and uses field investigations, radar scans, and other methods to investigate the occurrence of a series of defects in the tunnel, including lining splitting, water leakage, and tunnel bottom damage, to analyze the damage characteristics and occurrence mechanism in detail based on both external causes and internal causes. From the results, by combing relevant materials both in China and abroad with the engineering characteristics, a comprehensive management method for reinforcing and strengthening damaged tunnels with a reinforced concrete umbrella arch is proposed. At the same time, considering the degradation in the bearing capacity of the existing lining structure and utilization degree of the bearing capacity of newly increased reinforced concrete umbrella arch, this study performs a theoretical analysis of the calculation for the safety factor of the reinforced damaged tunnel. The calculation results show that the reinforced Liupanshan Tunnel is in a secure state, which can provide references for similar projects in the future. [ABSTRACT FROM AUTHOR]

• 90 operating highway tunnels with defects are analyzed. • Five characteristics of tunnel defects are studied. • A set of defect prevention and treatment process is proposed. • The preventive measures and treatment measures are listed and analyzed. The number and length of highways in China far exceed those in other countries. Therefore, to better understand the defects that have occurred in Chinese highways that are currently in service, we collected data on the defects in 90 such tunnels. Using these data, we conducted a systematic study on the causes of such defects. Based on the characteristics thus obtained, the defects could be divided into seven categories: structural deformation, structural damage, material deterioration, water leakage, frost damage, construction defects, and others (accessory facility defects). The results reveal that lining cracks and water leakage are the most common defects in the highway tunnels of China. These tunnel defects can be categorized based on their risk, correlations, visibility, regional characteristics, and progressive nature. Human activities are the primary cause of highway tunnel defects. The treatment measures for such tunnel defects in China can be categorized as additional, repair, and replacement measures; these measures are selected based on actual requirements of addressing the defects. Lastly, corresponding preventive measures and disposal procedures are established based on the abovementioned analyses. The results of this study are expected to serve as a reference and provide significant guidance for the prevention and treatment of road tunnel defects. [ABSTRACT FROM AUTHOR]