Crystallization Clogging in Highway Tunnel Drainage Systems: Characteristics and Detection Techniques

To clarify the characteristics and disaster-causing mechanisms of crystalline diseases in tunnel drainage systems and to evaluate the adaptability of detection equipment, field investigations were conducted on crystalline diseases in 31 tunnels across nine regions of China. Groundwater and crystal samples were collected and analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Detection equipment was classified into imaging-based and spectral-based categories, and their applicability was evaluated through case studies of Guanyinshan Tunnel and Anba Tunnel.The results indicate that calcium carbonate (CaCO3) is the dominant component of the crystalline deposits, with an average content of 95.741%, and that groundwater in all investigated tunnels is alkaline with a high proportion of scale-forming ions. According to structural location, tunnel crystalline diseases can be classified into five types: wall, pavement, inspection well, drainage ditch, and drainage blind pipe crystalline diseases. Case analyses show that pipeline periscopes, CCTV inspection robot vehicle, and LiDAR are suitable for detecting crystalline diseases in drainage ditches, although further development is required to improve their adaptability to tunnel environments. Pipeline endoscopes are effective for detecting crystalline diseases in small-diameter drainage blind pipes, while ground-penetrating radar (GPR) is limited to auxiliary positioning.Furthermore, the combined use of imaging-based and spectral-based detection equipment enables a transition from full-length comprehensive inspection to point-to-area detection, significantly reducing the detection workload. This study provides technical support for the detection and identification of crystalline diseases in tunnel drainage systems and offers a reference for the selection and development of detection equipment.