## 3 Results and Discussion
### Measuring the Profile with a Caliper  
The results shown in Table 3 were obtained by manually measuring the diameter of the upper (top) and lower (bottom) cutter rings of the double disc cutter. A total of 36 measurements were taken. The average value of the diameter of the upper (top) cutter ring, which considers all 18 profiles, is 274.096 mm. The maximum value of the measured diameter is 274.160 mm, the minimum value is 274.020 mm. The standard deviation is \(\pm\)0.042 mm. For the lower (bottom) cutter ring, the average value is 274.201 mm, the maximum value is 274.260 mm, and the minimum value of the measured diameter is 273.840 mm. The standard deviation is \(\pm\)0.095 mm. The scatter of the measured values around the mean value (dispersion) is higher on the lower (bottom) cutter ring of the disc cutter (\(\sigma^{2}=0.009\)). The main reason for this is obviously the measurement on profile 6-6, where there is medium-sized localized damage on the surface of the disc cutter.  
Considering both sides of the double disc cutter, the average total diameter is 274.148 mm (\(\pm\)0.0946 mm).  
The diagram in Figure 11 shows the measured diameters for the upper (top) and lower (bottom) cutter ring according to the profile of the disc cutter. The reduction in diameter due to medium-sized localized damage on the lower profile 6-6 is clearly visible.  
In general, there are no major deviations in the manual measurements of the disc cutter ring diameter by the individual profiles. This indicates that both cutter rings were worn relatively evenly during their use on the micro-TBM's cutter head, which also applies to the entire double disc cutter. According to the measured diameters of the cutter rings, there are several smaller instances of localized damage and one larger one. This can be determined without a prior macroscopic visual inspection of the disc cutter. A deviation in the diameter of a particular profile or several profiles from the neighboring profiles is an indication of the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Top Cutter Ring** & **Bottom Cutter Ring** \\
**Profile** & **Degree Circle** & **Diameter** & **Diameter** \\
**(/)** & (°) & **(mm)** & **(mm)** \\ \hline
0–0 & 0–180 & 274.12 & 274.22 \\
1–1 & 10–190 & 274.12 & 274.22 \\
2–2 & 20–200 & 274.12 & 274.12 \\
3–3 & 30–210 & 274.02 & 274.2  
highly probable possibility of the presence of localized damage. According to the diameter measurements, the largest localized wear damage is present on the lower (bottom) cutter ring. A diameter of 273.840 mm was measured for profile 6-6. This diameter deviates 0.361 mm from the average value of the diameter measurements on the lower (bottom) cutter ring. The diameter on the neighboring profile 5-5 is 274.140 mm, and on profile 7-7, is 274.240 mm. If there was localized damage in the form of removed material (chipping) between the labeled profiles on the cutter ring, this could not be detected by measuring the diameter along the profile. According to the photos taken during the macroscopic visual inspection, there are several such cases: obvious damage between profiles 16-16 and 17-17 on the upper cutter ring and some minor damage of a small size.  
The original diameter of the new double disc cutter is 330.2 mm (13). The worn diameter of the disc cutter is 274.148 mm if the average value of both cutter rings is considered. The original diameter was reduced by 56.052 mm or 17% due to abrasive wear. In other words, the profile of the disc cutter was reduced by an average of 28.026 mm. The original diameter and the worn diameter with the corresponding worn surface of the disc cutter are shown schematically in Figure 12.  
Figure 11: Diagram showing the diameters of the upper (yellow) and lower (grey) cutter rings of the double disc cutter measured using a caliper.  
Figure 12: Original (d\({}_{0}\)) and average worn (d\({}_{1}\)) diameters of the double disc cutter. The worn surface is colored yellow.