Degradation of engineering structures is an inevitable process. Maintenance provides ways to fulfill the requirements on safety and functionality under financial constraints. A large proportion of tunnels in Taiwan deteriorate within 20–30 years after construction because of active plate movement and increasing extreme climate events. In some special cases, tunnel degradation persist for a long time until adequate rehabilitation were held according to the deteriorating mechanism. Thus, accurate structural health monitoring, proper interpretation on monitoring data, accurate performance prediction and timely rehabilitation are the fundamentals to tunnel maintenance. Focusing on a methodology to clarify the interaction between degradation features of tunnels, this research monitored a tunnel for over four years. In successive processing and comparison on monitored tunnel displacements and lining cracks, the turning point of tunnel degradation can be identified.
Although some underground structures survived over 12,000 years (Kusch & Kusch 2009), there are areas around the world where tunnels degrade in a rate much higher than the average (Aydan 2015, Chiu et al. 2014, Konagai et al. 2009, Lee & Wang 2015, Sandrone & Labiouse 2011, Wang 2010, Wang & Chen 2001, Wu et al. 2014). For example, a large proportion of the tunnels in Taiwan and Japan deform and crack after construction complete for only several years (JSCE 2003, Chiu et al. in press). Among the cases, there are some tunnels deteriorate so severely that it continues after rehabilitated for several times. Thus, it is essential to understand the time-dependent behavior of operational tunnel cases before we achieve a true life-cycle based tunnel maintenance.
Abnormal phenomena in tunnels, also known as tunnel anomalies or pathologies, are possibly to be induced by changing environment and/or deteriorating engineering structures. The often mysterious cause induced tunnel deformation then proceed to produce cracks on tunnel lining. Therefore, the most straightforward methodology of effective tunnel maintenance is to establish the relationships between anomaly cause, tunnel deformation and lining cracks.