Field and laboratory study of cracking and safety of secondary lining for an existing highway tunnel in loess ground

Abstract

Lining cracking is a common distress for most existing highway tunnels in loess ground, and the development of such distress will directly affect the operation and service life of the tunnel. This paper studied the deformation evolution laws, cracking mechanism and failure process of the secondary lining for an existing highway tunnel in loess ground by carrying out field investigations and laboratory model tests. To simulate the field loading conditions more realistically, a 1: 10 large-scale test platform was developed and the loads acting on the lining model were determined according to the field measured pressure data. The statistical analysis of field tunnel distress indicates that the vault cracks more seriously than the sidewalls. The model test results show that the deformation and failure process of lining structure can be divided into three stages with two dividing points of vault cracking and inverted arch cracking. The intrados of vault and extrados of arch foot crack by tension, whereas the intrados of sidewall cracks owing to the high localized compression. The vault cracks first and exhibits the most serious cracking. Moreover, critical cracking zone is formed in vault, which finally makes the entire structure lose its load carrying capacity. Test results were compared with the characterization of field tunnel distress to validate their reliability, and conclusions regarding the safety assessment of studied tunnel sections were developed based on the comparison. The methods and findings of this study can serve as useful references for optimal design and long-term safety of tunnel structures.