Tunnel liner cracks significantly threaten structural stability and public safety, necessitating robust inspection and maintenance strategies. A structural health assessment based on tunnel inspection is performed to detect, identify, measure, and assess the severity of such a defect. For this reason, twin highway tunnels were considered, and liner cracks stretching over the vertical wall and roof arch were identified and measured by visual inspection. Then, NDT methods were employed on sound and cracked (cracks greater than 3 mm in width) parts of concrete. Moreover, a significant comparison was made to discern the quality of concrete between cracked and uncracked portions of the tunnel liner. Our findings indicate that cracked areas exhibit significantly lower compressive strength, as the UCS of the cracked liner was measured to be less than 69 N/mm2 and altered ultrasonic properties, suggesting deteriorating structural health. These discrepancies highlight the importance of targeted maintenance strategies to prevent deterioration and potential failure. Furthermore, statistical analysis was performed b/w sound and cracked concrete liner. Finally, specific and targeted repair measures such as surface sealing, epoxy injection, and grouting were recommended based on the severity and characteristics of the observed cracks. These measures could be implemented depending on the need and nature of the cracks. Overall, this research contributes to the field of civil engineering by providing a detailed assessment of tunnel liner defects and reinforcing the role of NDT in effectively managing tunnel infrastructure. The results serve as a valuable reference for enhancing tunnel operation safety protocols and maintenance practices.