Effect of Stress Ratio K due to Varying Overburden Topography on Crack Intensity of Tunnel Liner

A structural health assessment of the tunnel lining is carried out to investigate and mitigate the cause of defects in the tunnel lining to ensure user safety. Many factors affect the tunnel's integrity, causing a wide range of defects. Identifying the possible cause and its relation with the degree of associated defect is essential for tunnel stability. In conjunction with defects of tunnel failure, liner cracks were found to be most critical because they could trigger other defects to form and jeopardize tunnel stability. Thus, this research acquires visual inspection followed by comprehensive mapping and quantification of liner cracks to enhance our understanding of the effect of varying overburden on the intensity of liner cracks. The numerical analysis was further performed to analyze the influence of varying topography (overburden) on the crack intensity of the liner using the stress ratio, K as a parameter in terms of the state of stress using induced stress (IS) and stress concentration factor (SCF) as a performance evaluation criterion. The work demonstrates that the shift in magnitude and position of liner cracks on the different portions of the tunnel liner implies the effect of a regionally external factor (varying overburden depth) on tunnel degradation. For advances in tunnel assessment based on the regional diversity of cracks along the longitudinal profile of the tunnel, the tunnel should be divided into zones based on the overburden to identify the varying intensity of the liner crack. This study shows the variable crack density of 575 m to 628 m, 650 m to 700 m, and 704 m to 724 m for shallow, intermediate, and deep zone, respectively. The findings of this study can provide scientific guidance to tunnel inspectors and engineers regarding the tunnel liner health assessment and identifying the subsequent method of repair.