Recent researches about tunnel maintenance focused on characterizing the crack patterns and displacement modes of operational tunnels, since crack and displacement are the two most common lining anomalies. Aiming on the relationships between tunnel displacement and crack patterns, this research proposes a model that can demonstrate crack patterns induced by relative motion at the two ends of a tunnel region. The definition of relative motion within a tunnel region comes from the fact that a tunnel was formed with regions separated by construction joints, and that traditionally displacement monitoring was conducted on selected tunnel profiles. A numerical model utilizing elastic rock mass and lining with concrete damaged plasticity is established to compute the stress, strain and to show the lining crack due to relative translation, rotation, and some basic deformation. Relative horizontal and vertical translation create diagonal inclined cracks, whereas the former display slashes on tunnel vault and invert, and the later produce slashes on tunnel sidewall. The relationship between crack patterns and relative displacement proposed in this research were verified by comparing with years of detailed digital lining records and high precision monitored displacement of a rock tunnel in Taiwan.
From the over one hundred years' experience of tunnel maintenance, it is found that lining anomalies emerged in a high proportion of tunnels. The degradation of tunnels continued until proper measures to anomaly causes been taken. However, the investigation of anomaly causes was always obstructed by the complicated anomaly appearances, the insufficient monitored data, and the unclear mechanism between causes and anomalies. Many developed countries has regarded maintenance of infrastructures as the critical issue to sustainable operation. Recording, observing and measuring the variation of cracks is one of the most straightforward way to gain the integrity degree of a structure. Recent researches about tunnel maintenance put emphasis on anomaly patterns, make efforts on the relationships between anomaly patterns and anomaly causes in order to repair and reinforce tunnel adequately, reducing the proportion of repeat rehabilitation without identifying the anomaly cause (Japan Society of Civil Engineers, 2003; Chiu, 2014; Asakura et al., 1994). Methods to characterize lining anomalies has been proposed (Lee and Wang, 2014; Chiu et al., 2014), however, the connections of one type of anomaly to another are still unclear. Since lining anomalies were generally produced by multiple factors (Japan Society of Civil Engineers, 2003), it is necessary to understand the relation of anomaly patterns and their causes.