## 3 Results
### Territorial Scale Analysis  
The subsidence effects induced by the excavation of the two subway tunnels can be observed in the years since 2017. In this period, the construction of the first section began with excavation performed using two TMB excavators. However, the entire route of the T3 section cannot be studied because it had not been finished by March 2019, which is the last time for which data are available. In detail, within this period, the excavations concerned the route from the station of San Giovanni to shaft 3.2, located in an intermediate position between the Amba Aradam/Ipponio station and the Colosseum, as shown in Figure 2. As a result, the area in which the displacements can be analyzed is further reduced.  
The dataset contains the displacements along the LOS, which are used to evaluate the average annual velocity along the LOS. Figure 3 reports the velocity (cm/yr) on the map in the period from 2017 to 2019, while Figure 4 refers to the period from 2014 to 2016 and is used for comparison. It is worth observing that, in the period of the excavation (Figure 3), the velocity distribution presents a higher number of points with negative measures when compared to the previous years (Figure 4). These points are shown in yellow or red, and the negative value indicates that they are moving away from the satellite orbit, so they are qualitatively correlated to the subsidence phenomenon. As shown by the presence of negative values in Figure 4, it is not possible to exclude the possibility that subsidence also occurred before the construction of the metro line, for reasons uncorrelated with the excavations. However, it can be noticed how the points with negative velocity values strongly cluster along the subway route in Figure 3. Moreover, the underground work proceeded from the east of the reported area, moving westward; this may explain the larger concentration of these points on the rightmost portion of the figure.  
Figure 3: Map showing the dispersion of the average annual velocity along the LOS in the period from 2017 to 2019. The route in black refers to the part already under construction; the route in grey refers to parts not yet built.  
Figure 2: Map showing the T3 section of the Line C subway, the stations, the inter-tract shafts and the interaction with the other subway lines, Rome (Italy), edited from ([[https://goo.gl/maps/zPUUjveLSWBzj7](https://goo.gl/maps/zPUUjveLSWBzj7) nC9]([https://goo.gl/maps/zPUUjveLSWBzj7](https://goo.gl/maps/zPUUjveLSWBzj7) nC9), accessed on 28 January 2022), [27].  
To quantitatively study the subsidence phenomenon in the period from 2017 to 2019, the probability distribution of velocity values is estimated. Assuming a Gaussian distribution, the values have a mean equal to \(\mu=0.0440\) cm/yr and a standard deviation equal to \(\sigma=0.4132\) cm/yr. This distribution allows identifying the negative outliers, points that deviate most from the general behavior of the distribution on the negative branch, in which the velocity is lower than \(\mu-3\sigma\), that is to say, all the points with less than 0.14% probability of belonging to the same statistical distribution. From a physical point of view, these outliers can be interpreted as locations where subsidence is particularly prominent.  
As seen in Figure 5, although the points outside this lower threshold are not exclusively distributed along the track, approximately 52% of them are concentrated in the route proximity (route \(\pm\) 150 m). These points fall mainly on the route between San Giovanni station and the intermediate station of Amba Aradam/Ipponio, where the depth of the tunnels is about 30 m. On the other hand, in the latter part, the depth increases up to 57 m at shaft 3.2. Moreover, this portion of the track has been subjected to excavations near the end of the period for which data are available, so it was expected to find fewer points outside the threshold. The presence of excavation-induced subsidence was also confirmed in other studies [28; 29].