Examining Distribution Characteristics and Causes of Cracks on Tunnel Lining Structure in Mudstone Stratum

Cracking is a common problem in tunnel linings, and mudstone is widely distributed in southwest China. Hence, it is necessary to explore distribution characteristics and causes of cracks on tunnel lining in a mudstone stratum. This paper presents a case study of the Xishanping Tunnel in China, aiming to investigate distribution characteristics and causes of lining cracks within the mudstone stratum. A quantitative analysis was conducted after collecting crack data to investigate the distribution characteristics. Factors influencing lining cracks were examined based on experimental tests, nondestructive detection, and numerical simulation. Sixteen crack data points were collected through field investigation. The quantitative analysis revealed that cracks at the vault, with lengths between 0 and 5 m and widths between 0 and 3 mm, occupied the most significant proportion. Furthermore, the most significant proportion of cracks was found in the vault at different width intervals. The experimental test revealed that the mass percent of montmorillonite in mudstone is 33%, and the surrounding rock is classified as an enormously expansive rock. The expansion of surrounding rocks squeezed the lining structure, which may lead to lining cracking. The analysis of nondestructive detection data showed that there were either cavities or inadequate thickness at the location of most cracks. Numerical simulation results indicated that when there are cavities and inadequate thickness underneath the lining, the principal tensile stress of the lining exceeds the acceptable limit (0.55 MPa), causing the lining to crack. Therefore, lining cracks are caused by two factors: (1) expansion of surrounding rocks, and (2) inadequate lining thickness and cavities beneath the lining. The findings reported in this work can provide the design basis for appropriate maintenance of the damaged lining structure in tunnels excavated within the mudstone stratum.