Effects of stress-ratio on crack intensity in tunnel lining

Abstract

Tunnels after serving period over time needs to be inspected and maintained for them to perform without any structural failure and posing no hazard to the ongoing traffic. Structural health assessment of tunnel lining is carried out to investigate and mitigate the cause of defects in tunnel lining to ensure user safety. In conjunction with other tunnel liner defects, liner cracks were found to be considered as the most critical defect because of their potential to trigger subsequent defects and cause tunnel instability. Until now, the relationship between the developing anomalies in tunnel liner and their cause is still unclear and studies have addressed the cause of liner crack due to topography (in terms of overburden) on the stability of tunnel liner, especially for the varying overburden. The research mainly aims at understanding the effect of varying overburden on liner cracks. For this purpose, visual inspection was conducted and cracks in the tunnel liner were mapped and quantified and numerical analysis was performed to see the effect of varying topography (overburden) using parameter Stress-Ratio (K) on the intensity of liner in terms of state of stress-displacement using Induced Stress (IS) and Stress Concentration Factor (SCF) as a performance evaluation criteria’s. The result from this study shows the shift in magnitude as well as position of crack density along different portions of tunnel liner with varying overburden depth. Moreover, based on the regional diversity of crack along longitudinal profile of tunnel for advances in tunnel assessment, tunnel was divided into zones based on the varying overburden with a view to identify varying intensity of crack on tunnel liner. The crack density increased with increasing overburden depth such as shallow zone is ranging from 0 to 96 m overburden depth with crack density (575 m to 628 m), while transition zone has range from 97 to 160 m having density (650 m to 700 m) whereas the overburden depth for deep zone with denser cracks at vertical wall and lower hance portion ranges from 161 to 204 m with crack density (704 m to 724 m). On the basis of results, the method applied for mapping and quantification of crack can serve inspectors and owners of tunnels for technical guidance to conduct health assessment of tunnel liner.