Automatic inspection and assessment of a cross-passage twin tunnel using UAV

The inspection of large-scale tunnel networks is essential to identify any long-term deterioration mechanisms. Traditional manual inspection is not automatic and adaptive in geometrically complex tunnel configurations. This paper presents an automatic unmanned aerial vehicle (UAV)-based tunnel assessment application in a critical cross-passage twin tunnel section of Dublin Port Tunnel. It adopts a reactive method for UAV navigation and photogrammetry, and a point cloud for data processing. This study specifically verifies the patterns of cross-section deformation and defect distribution in twin tunnels and discovers that the deterioration pattern agrees with previous monitoring results. It shows that observed tunnel deformation could be attributed to the effect of twin tunnel interaction and vehicle cross passage, whilst the distribution of lining cracks could be associated with the differential structural stiffness and the differential longitudinal bending along the tunnel section. • Methodology PMPP-SDI in UAV control validated in a diameter-variant tunnel. • Comprehensive image processing workflow based on UAV-acquired images presented. • Deformation profiles obtained through comparing generated and as-built cross-sectional profiles. • Lining cracks and water leakage identified and quantified through orthomosaiscs. • Underlying mechanisms behind the observations in tunnel deformation and defect revealed.