# Performance Analysis of Tunnel Boring Machines for
## 2 Data Collection for Performing Statistical Analysis
### Analysis of Correlations Based on the Type of Rock Crossed
#### 2.2.3 Double Shield TBM  
For this type of machine, data coming from the excavation in four kinds of rocks were available: granite, sandstone, limestone, and schist. From the analysis performed in granite, the correlations between the diameter and the power supplied to the excavation head (Figure 17) and between the diameter and the torque (Figure 18) were analyzed. In the first case, the 13 experimental data are approximated by a linear function (R\({}^{2}\) = 0.9114), whereas in the second case the regression function is a power (R\({}^{2}\) = 0.7645). In both cases, the low data dispersion suggests that the excavation was performed in rock formations having a similar geomechanical behavior. Correlations in sandstone are very high. Figure 17 shows the trend of the power supplied to the excavation head vs. the diameter, represented by a linear equation with coefficient R\({}^{2}\) equal to 0.9166. The function that correlates the diameter and the thrust is an exponential (Figure 19), which approximates very well the experimental points for diameters between 2 and 6 m; with a diameter of 10 m, three very different thrust values are evident. Figure 16: Correlation between the power and the torque due to the excavation in sandstone and limestone by single shield TBMs. Figure 17: Correlation between the diameter and the power due to the excavation in granite, sandstone, limestone, and schist by double shield TBMs. Figure 19 shows the torque trend vs. the diameter. The two parameters are well correlated, and the experimental points are perfectly represented by a power function (R\({}^{2}\) = 0.942). The range of diameters is between 2 and 10 m, while the torque varies between 200 and 23,000 kNm. A single \"anomalous\" experimental point is evident, represented by a machine with a diameter of 10 m and a torque greater than 40,000 kNm. Additionally, in the limestones there are good correlations between the mechanical parameters of this type of machine: The exceptions are represented by the diameter vs. the cutterhead power (R\({}^{2}\) = 0.627, Figure 17) and the diameter vs. the thrust (R\({}^{2}\) = 0.4563, Figure 18). There are, instead, excellent correlations between the diameter and the torque, with R\({}^{2}\) equal to 0.9067 (Figure 19). As for the shales, the correlations between diameter and power (Figure 17) and diameter and torque (Figure 19) were analyzed. In the first case, the regression function is linear, with R\({}^{2}\) = 0.8378; the experimental data are mainly concentrated in a range of diameters between 3 and 8 m, corresponding to power values between 200 and 2500 kW. In addition, two isolated points with a 10 m diameter are identified, which are associated with two power values greater than 4 MW. In the second case (Figure 19), the exponential trend of the torque vs. the diameter is given (R\({}^{2}\) = 0.892). In both cases, the deviation from the average is small. As for the open TBM models, from the analysis of the graphs in Figures 20 and 21, it appears that the trends of the power supplied to the excavation head vs. the diameter and those of the torque vs. the diameter are linear for all the case studies analyzed. On the other hand, a difference (Figure 22) is noticeable between the shape of the function which expresses the trend of the thrust vs. the diameter (logarithmic), obtained in the present study, and the experimental, linear equation obtained from [42]. However, with the same diameter, the thrust values are very similar, and the discrepancy is probably related to the different amount of data analyzed. In case of single shield TBMs, it was not possible to validate the forecast model expressing the correlation between the diameter and the power supplied to the excavation head. The correlations between torque and diameter (Figure 23) and between thrust and diameter (Figure 24) are represented by power functions. Finally, validation was sought for double shield TBMs.