Structural safety of in-service motorway tunnel linings under defective conditions

Abstract The structural safety of in-service tunnel lining structures is assessed and calculated using a numerical simulation based on the damage statistics of a motorway tunnel to study the effects of the surrounding rock classification, defect type, defect location, and severity of defects on the lining. The main conclusions are as follows. (1) Void defects mainly exist in the shoulder section and account for 73% of the total defects, whereas insufficient thickness is primarily observed at the sidewalls, accounting for 52% of the total defects. (2) As the width clearance of the tunnel increases, the safety factor of each region on the lining structure is reduced to different extents. Voids in the crown section have the highest impact on the safety factor of the lining structure. When the maximum width exceeds 2 m, the safety factor is reduced by up to 91.92%. (3) When the tunnel lining is insufficiently thick, the influence of the defect generally does not extend beyond the defective area. The maximum reduction rates of the safety factors for the crown, shoulder, and sidewalls are 91.28%, 96.12%, and 90.48%, respectively. (4) Thickness defects are more prevalent than void defects. Compared with insufficient thickness defects, void defects more considerably affect the safety factor of the lining structure. Hence, the results of this study can provide an engineering basis for the operational status of in-service tunnels.