## 4 Field Test
These were compared with the 2D models obtained by separately inverting only the calculated measures relative to the parallel A\(-\)A\({}^{\prime}\), B\(-\)B\({}^{\prime}\), C\(-\)C\({}^{\prime}\) and D\(-\)D\({}^{\prime}\) lines, using RES2 DINV. Finally, of these four lines, two 2D ERTs (A\(-\)A\({}^{\prime}\) and C\(-\)C\({}^{\prime}\)) were actually carried out in the field using the MAE X612-EM\(+\) multichannel resistivity meter. Due to some subsidence of the ground, which was probably caused by the collapse of the roofs of some cavities, it was not possible to carry out lines B\(-\)B\({}^{\prime}\) and D\(-\)D\({}^{\prime}\). The data obtained were used to make a comparison between the simulated and observed data. Section A\(-\)A\({}^{\prime}\) (Figure 12a) intersects tunnels \(H\), \(J\) and \(L\) and the large chamber \(M\) partially filled with waste material. Furthermore, tunnel N is present in the vicinity of the survey line (Figure 11). Overall, the section of the inverse 3D model (Figure 12b) obtained starting from the simulated data was faithful enough to the original geoelectric model. In fact, the large chamber \(M\) was highlighted well in terms of its shape, as the two tunnels \(H\) and \(L\) were highlighted by two smoother anomalies with lower resistivity values, while tunnel \(J\) was incorporated into chamber \(M\). The inverse 2D model (Figure 12c) obtained starting from the simulated data while returning a comparable data misfit value showed a lower adherence of the shapes and, above all, an anomaly in correspondence with the projection on the section of chamber N, which was not crossed by the section. The inverse model relating to the field measurements (Figure 12d) was quite similar to that obtained from the simulated data, except for the more superficial areas in which heterogeneous trends and higher resistivity values were noted. This can be explained by the presence of fill materials and more fractured calcarenite, which also justified the higher value of the misfit. Figure 11: Perspective view of the simplified 3D resistivity model of the Fodera Quarry obtained by RES3 DMOD\({}^{\text{TM}}\) software. The yellow letters indicate the main rooms and tunnels. The blue dashed lines indicate the traces of the simulated 2D ERTs. Section B\(-\)B\({}^{\prime}\) (Figure 13a) intersected the four main tunnels \(H\), \(J\), \(K\) and \(L\), being elongated perpendicular to the section, but it was also affected by the connecting gallery \(N\) with a direction parallel to the section. Furthermore, gallery \(R\) was very close to the survey line (Figure 11). Figure 12: Line A\(-\)A\({}^{\prime}\) comparison between simulated inversion of 3D and 2D resistivity surveys and 2D inversion of field data. (**a**) Corresponding section of the 3D resistivity model. (**b**) Vertical section of the inverse model obtained by simulating a 3D survey on the geophysical model. (**c**) Inverse model obtained by simulating a 2D survey on the geophysical model. (**d**) Inverse model obtained by 2D ERT field data. The section of the 3D inverse model (Figure 13b) obtained from simulated data represented the geometric shapes of the intersected cavities quite well, although the anomalies showed resistivity values well below the values of the model. The 2D inverse model (Figure 13c) obtained from the simulated data, even if it showed a data misfit value similar to that of the 3D model, was less faithful and had more blunt anomalies. Furthermore, between \(x=74\) m and \(x=92\) m, there was an anomaly caused by gallery \(R\) not being crossed by the survey. Section C\(-\)C\({}^{\prime}\) (Figure 14a) had a very complex shape. It intersected the main tunnels \(H\), \(J\), \(K\) and \(L\) but also the connecting tunnel \(R\) and a small room \(P\) connected to gallery \(N\). Furthermore, the section passed close to gallery \(S\), which connected \(H\) with \(J\).