# Structural Health Monitoring of a Road Tunnel Intersecting a Large and Active Landslide
## 4 Results  
Data have been collected through the monitoring system for three years; each year is considered to run from April to the following March since monitoring started in April 2014. During the first year, the cumulated rainfall was 1926 mm, exceeding the site average of 1700 mm/year as there were some intense rainfall events (e.g., in November 2014 the cumulated rainfall reached 700 mm in 20 days). Rainfall was lower in the second (1512 mm) and third years (1190 mm/year), with no significant rainstorms. The fact that we have been able to observe the landslide/tunnel dynamic over three years under different climate conditions permitted the analysis of the effect of water inputs on the system. Twenty-two out of the 24 crackmeters have measured higher cumulative absolute displacements in the first year (Figure 8). The remaining two instruments recorded higher cumulative absolute displacement in the second year, but the magnitude of the displacement and the difference between the two rates is small. Most of the instruments showed a seasonal signal overlapping the widening trend. Since the declared thermal drift of the deployed sensors is extremely small, we suppose that this behaviour is linked to the response of the concrete to variations in temperature and humidity, with little dilatation during the summer. Figure 8: Displacement recorded by the crackmeters deployed across the tunnel cracks—the graph has been produced directly through the web-based platform. Figure 7: Screenshot of the colour/arrow map for the tunnel monitoring system in the web-based platform. Among the crackmeters installed on the cracks of the vault (1-16), three have been accumulating displacements above the 0.3 mm threshold in the three-year monitoring period, namely F07 (0.36 mm), F11 (0.42 mm) and F13 (0.47 mm). For all sensors, the majority of the displacement was recorded during the first year: the greater deformation rates reached 12 \(\upmu\)m/day in F13 and 9.2 \(\upmu\)m/day in F11 between November 2014 and March 2015, a period with significant rainfall events. In Figure 9 displacements of three sensors, all located in segment 28, are plotted with the water discharge of the drainage system within the road tunnel. The eight crackmeters installed between the tunnel segments have been measuring larger displacements, as expected. Based on the collected data, these sensors could be grouped into two clusters: the first comprising the crackmeters in the external segments (F17, F24, F20 and F21) and the second comprising the crackmeters in the internal segments (F18, F19, F22 and F23). About the first group, the maximum cumulated displacement recorded in the three-year period is relatively small, with a maximum displacement of 0.19 mm measured by F17, while for the second the displacement is significantly higher, with a maximum displacement of 6.47 mm measured by F23. Data regarding the internal segments extensometer group are shown in Table 1 and displacements over time can be found in Figure 10. \begin{table}
\begin{tabular}{l c c c c} \hline  & **F18** & **F19** & **F22** & **F23** \\ \hline
**Cumulative displacement over three years** & 1.25 mm & 4.88 mm & 3.17 mm & 6.47 mm \\ \hline
**Displacement rate over three years** & 10.5 \(\upmu\)m/day & 37.30 \(\upmu\)m/day & 24.24 \(\upmu\)m/day & 48.34 \(\upmu\)m/day \\ \hline
**Displacement rate between November 2014 and March 2015** & 23.44 \(\upmu\)m/day & 89.04 \(\upmu\)m/day & 63.17 \(\upmu\)m/day & 115.09 \(\upmu\)m/day \\ \hline \end{tabular}
\end{table} 
Table 1: Data for internal segments group of crackmeter. Figure 10: Displacements recorded by the internal segments crackmeters in the three-year period—the graph has been produced directly through the web-based platform. Figure 9: Displacement recorded by crackmeters F07, F11 and F13 plotted with the water discharge recorded in the drainage system within the road tunnel—the graph has been produced directly from the web-based platform.