Quantitative condition inspection and assessment of tunnel lining

To ensure the safety and the serviceability of underground structures, routine inspections and maintenance processes are essential for their optimal use. Presently, the practical inspection of tunnels depends on human-based methods, which has inherent limitations. This study proposed a quantitative system for the health inspection and assessment of the tunnel lining. The system is capable of acquiring and extracting cracks or other defects efficiently, drawing crack charts automatically and assessing the situation of tunnel lining with a much more accurate index. The consistency of the cracks automatically extracted by the proposed tunnel lining inspection system is verified with the investigation of two tunnels using different construction methods. For the health assessment of tunnel lining, a valid index is introduced to evaluate the lining status according to the fractal dimension of cracks. Results of the comparative tests and field tests indicate the validity of crack fractal dimension D. In addition, results of several real cases on field tests demonstrate its practicability. Such a system can achieve time-saving automated surveying solutions with fast data acquisition, identification and documentation of cracks as well as detection of structural changes. For an all-around assessment of the health situation for tunnel lining, the influence of strength characteristics of the tunnel lining due to its irregular shape should be taken into consideration in future research.