## 3 Field Test
### System Monitoring  
Monitoring of the developed system installed at Seungbu tunnel, was performed from 22 December 2021 for three weeks in order to estimate its applicability. The thawing-guided drainage system was operated with 150 W of power, based on the lab test for optimal electric power consumption. The internal temperature of the thawing-guided drainage system and the ambient temperature are illustrated in Figure 9. The maximum, minimum, and average values of the internal temperature of the system and the ambient temperature for each day over the 3-week test duration are arranged in Table 4.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**Temperature Day** & **Min.** & **Max.** & **Avg.** & **Day** & **Min.** & **Max.** & **Avg.** & **Day** & **Min.** & **Max.** & **Avg.** \\ \hline Internal Ambient & Day 1 & 2.8 °C & 5.8 °C & 4.8 °C & Day 8 & 3.3 °C & 4.5 °C & 4.2 °C & Day 15 & 0.1 °C & 3.1 °C & 1.3 °C \\  & & 1.0 °C & 6.9 °C & 4.4 °C & & & & & & & & \\  & & & & & & & & & & & \\ \hline Internal Ambient & Day 2 & 1.8 °C & 5.9 °C & 4.1 °C & Day 9 & 0.7 °C & 4.5 °C & 2.7 °C & Day 16 & 0.4 °C & 4.1 °C & 3.7 °C \\  & & & & & & & & & & 2.6 °C & 4.9 °C & 2.9 °C \\ \hline Internal Ambient & Day 3 & 3.3 °C & 5.8 °C & 4.9 °C & Day 10 & 0.3 °C & 3.9 °C & 3.9 °C & 1.5 °C & 1.5 °C & Day 17 & 0.3 °C & 4.1 °C & 1.7 °C \\  & & & & & & & & & & & \\ \hline Internal Ambient & Day 4 & 1.0 °C & 5.2 °C & 3.9 °C & Day 11 & 0.1 °C & 3.0 °C & 2.2 °C & Day 18 & 0.2 °C & 3.6 °C & 2.5 °C \\  & & & & & & & & & & & \\ \hline Internal Ambient & Day 5 & 0.5 °C & 4.5 °C & 2.6 °C & Day 12 & 2.1 °C & 3.7 °C & 3.0 °C & Day 19 & 1.5 °C & 4.6 °C & 4.1 °C \\  & & & & & & & & & & & \\ \hline Internal Ambient & Day 6 & 0.9 °C & 2.8 °C & 2.1 °C & Day 13 & 2.0 °C & 3.6 °C & 3.0 °C & Day 20 & 1.6 °C & 4.7 °C & 3.5 °C \\  & & & & & & & & & & & \\ \hline Internal Ambient & Day 7 & 2.5 °C & 4.2 °C & 3.3 °C & Day 14 & 1.0 °C & 4.0 °C & 3.2 °C & Day 21 & 1.7 °C & 4.5 °C & 3.2 °C \\  & & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: The maximum, minimum, and average values of the internal temperature of the system and the ambient temperature over the 3-week test duration.  
Figure 8: Installation of thawing-guided drainage system: (**a**) location of installation in Seungbu tunnel (location of crack); (**b**) system installation; (**c**) infrared image of operating system.  
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 for the whole test period. For example, on day 2, the ambient temperature dropped up to \(-\)2.9 \({}^{\circ}\)C, and the internal system temperature simultaneously indicated a temperature lower than 0 \({}^{\circ}\)C. The internal temperature of the system indicated 0.1 \({}^{\circ}\)C when the ambient temperature was lowest at \(-\)9.7 \({}^{\circ}\)C during the test period. It is remarkable that the internal temperature of the system was maintained above 0 \({}^{\circ}\)C over the 3-week test period. The average internal temperature of the internal system for 3-week test period was 3.1 \({}^{\circ}\)C, and the ambient temperature was 1.2 \({}^{\circ}\)C. Therefore, a 150 W heater prevents the icing of leakage water in the conditions of Seungbu tunnel at which the field test was conducted.  
After the 3-week test period, a visual inspection was performed to verify the overall operating conditions. In terms of the inspection of component stability, there was no component separation inside and outside the system. In consequence of the visual inspection, neither icicles nor leaked water were found in the exterior of the system. Consequently, it was judged that the water had been stably drained through the drainageways. The proposed system was applied to the operational railway line, and thus, the operational safety of the system was also verified during the field test period.