## 5 Conclusions  
The performance of concrete structures degrades over time due to general aging. In Korea, the number of road and railway tunnels has rapidly increased. Due to terrain, geology, and local conditions, tunnels experience concrete deterioration and water leakage. In cold weather especially, safety measures are necessary to deal with water leakage occurring from cracks in old tunnels, which form icicles on the crown lines and frost (inverse icicles) on the tracks. A thawing-guided drainage system which prevents the formation of icicles has been proposed in this study. The system consists of heating panels along the tunnel surface, supporting stands arranged at consistent intervals along the tunnel surface, and guided drainageways that induce the drainage of leakage towards the side of the tunnel (outside of the track). The system has been designed and fabricated for verifying its field applicability through lab and field tests. In lab conditions, the prototype system was operated with 100 W of power, and then the power was gradually increased at 50 W increments up to 300 W of power. It was evident that the heating by the thawing-guided drainage system increased the internal temperature of the system irrespective of the applied power. Considering the minimum mean temperature of the installation site and simulating the extreme cold region, the internal temperature of the chamber was set to \(-15\)\({}^{\circ}\)C. The temperature distribution of a 100 W heater shows that the internal temperature was below 0 \({}^{\circ}\)C until after 34 min. Although the anti-freezing effect was confirmed because the average internal temperature was above 0 \({}^{\circ}\)C, the temperature temporarily dropped below 0 \({}^{\circ}\)C at a certain time. The system successfully maintained an internal temperature of 0 \({}^{\circ}\)C or above, even with an external air temperature of \(-15\)\({}^{\circ}\)C that replicates extreme cold during winter. For the field test, the thawing-guided drainage system composed of heating panels, supporting stands, and the drainageways for discharging leaked water has been fabricated. The system uses a 150 W heating module, which fundamentally prevents the formation of icicles from cracks in Seoungbu tunnel and induces the drainage of thermally melted icicles to the outside of the track. Through the field test, it has been investigated that the thawing-guided drainage system had also maintained an internal temperature of 0 \({}^{\circ}\)C or above even at ambient temperatures of about \(-10\)\({}^{\circ}\)C, and furthermore, the system effectively drained water leakage (thermally melted icicles). The proposed system was installed on the operational railway line in the field test. Through the field test, the icicle prevention performance was verified by maintaining the internal temperature above 0 \({}^{\circ}\)C over the whole 3-week test period, even at an ambient temperature of about \(-10\)\({}^{\circ}\)C. The operational safety was also verified as there was no component separation inside and outside the system. Therefore, it is judged that the applicability of the developed system has been verified in consideration of the following three aspects: usability in the operational railway line, effectiveness for thawing and guided- drainage performances, and operational safety without interrupting railway operation after installation. In this study, the applicability of the thawing-guided drainage system to the old railway tunnel was tested and verified. This system, however, can be applied not only to railway tunnels but to road tunnels and various infrastructures that require efficient thawing and drainage even in extreme cold regions. Even though the transportation technologies are steadily becoming more sophisticated, such as a subsonic capsule train or hyperloop system, sustainable thawing and drainage technologies for the old railway infrastructure are constantly required. Conceptualization, T.K. ; methodology, S.K., H.Y. and T.K. ; validation, S.K., T.K. and H.Y. ; formal analysis, S.K.