# Performance Analysis of Tunnel Boring Machines for
## 2 Data Collection for Performing Statistical Analysis
### Analysis of the Correlations Identified on the Basis of the TBM Type  
For the three types of machine selected (open, single shield, and double shield TBM), the cases found in the literature (whose number is summarized in Table 1) were analyzed in detail. As for the correlation between the diameter and the power supplied to the cutterhead (Figure 1), the trend identified is linear for open TBMs, with R\({}^{2}\) = 0.766. The graph shows that, with the same diameter, the power values vary in a more or less extended range. This is due to the different characteristics of rock masses crossed. Good correlations have also been found for single shield TBMs, through a power function where R\({}^{2}\) is 0.7833. It has to be noticed that large diameters were used in very different rock masses, so that their variation range is greater compared to smaller diameters. For each pair of parameters investigated, the number of experimental data analyzed was greater than 30. This made it possible to get more reliable models. As for the double shield TBMs, the relationship identified is linear, and the power supplied to the cutterhead increases with the diameter; R\({}^{2}\) is 0.7903. The number of data analyzed is, also in this case, consistent; the power varies between 200 and 6500 kW. However, most of data is in the range 200 to 3000 kW, with diameters between 2 and 9 m. Diameters smaller than 3 m did not provide enough experimental data to make a meaningful comparison; diameters between 3 and 5 m provided similar values for both open and double shield TBM; with a diameter greater than 5 m, the double shield TBMs are on average supplied with a power greater than the other types of TBM. \begin{table}
\begin{tabular}{c c c c} \hline  & **Open TBM** & **S.S. TBM** & **D.S. TBM** \\ \hline Diameter (m)—Power (k\(W\)) & 72 & 89 & 78 \\ \hline Diameter (m)—Torque (k\(\mathrm{Nm}\)) & 53 & 84 & 58 \\ \hline Diameter (m)—Thrust (k\(\mathrm{N}\)) & 53 & 21 & 77 \\ \hline Thrust (k\(\mathrm{N}\))—Torque (k\(\mathrm{Nm}\)) & 22 & 14 & 37 \\ \hline Power (k\(W\))—Torque (k\(\mathrm{Nm}\)) & 44 & 73 & 48 \\ \hline Power (k\(W\))—Thrust (k\(\mathrm{N}\)) & 34 & & 55 \\ \hline Diameter (m)—Rotation speed (rpm) & 24 & 17 & 48 \\ \hline \end{tabular}
\end{table} 
Table 1: Number of cases found in the literature to compare the main parameters of the Tunnel Boring Machines (TBM) analyzed. S.S.: single shield; D.S. : double shield. Figure 1: Correlation between the diameter and the power at the cutterhead for the three classes of TBM analyzed. Red: open TBM; blue: single shield TBM; green: double shield TBM. Similar results were obtained from the previously quoted study, carried out by [43]. They observed linear trends for open and double shield TBM, with R\({}^{2}\) = 0.6 in both cases and noticed that, the diameter being the same, the double shield machines are characterized by higher power; single shield TBMs could not be evaluated, due to lack of data. The trend of the torque vs. the diameter is given in Figure 2. The correlations are represented by a linear function in the case of open TBMs and by power functions for single and double shield TBMs. The results are in line with those obtained by [42]. It can also be noticed that in the whole domain, with the same diameter, single shield machines operate with a larger torque. In the range of diameters between 3 and 7 m, the performance of open TBMs and that of double shield TBMs are very similar. Over 7 m, the gap increases progressively as the diameter increases, and, for the same diameter, the open TBMs work with a lower torque compared to the other two types of machines. A higher concentration of data in the range of diameters between 2 and 9 m is also noticeable. Furthermore, in the same range, the range of the torque is small, and the model approximates the experimental points very well. A kind of correlation, expressed by a logarithmic trend, is observed in open TBM between the diameter and the thrust (Figure 3), characterized by R\({}^{2}\) = 0.6417.