## 4 Conclusions  
In this article, the wear of an MTBM disc cutter was evaluated using four different measurement methods. Using macroscopic visual inspection, profile measurement with a caliper, weighing, and close-range photogrammetry, various approaches for evaluating the wear of the double disc cutter were tested. The aim of this study was to compare different methods of assessing wear and to construct the profile of a worn double disc cutter based on a point cloud obtained from close-range photogrammetry measurements. The main conclusions from the comparison of the different wear assessment methods can be summarized as follows:  
1. During the macroscopic visual inspection, the type of wear on the double disc cutter was defined as normal abrasive wear with some localized cutter chipping. In general, macroscopic visual inspection is a very suitable method for determining the wear type of TBM disc cutters. It is a time-saving method that does not require any special equipment and can be performed even if the disc cutters are still installed on the TBM cutter head. It is recommended to be performed in addition to all other methods. 2. Profile measurements were taken every 10\({}^{\circ}\) on both sides of the disc cutter ring (top and bottom) using a manual vernier caliper. This method is more time-consuming than the previous one and requires a caliper with sufficient capacity that is larger than the diameter of the disc cutter. The caliper method provides information on whether the wear is uniform or not. It can also detect some localized defects that manifest themselves as plastic deformation or material loss. 3. The mass loss of the disc cutter was determined by weighing it using a digital hanging scale. This method is easy to perform and requires a scale with sufficient capacity and an additional tool such as a crane to lift the disc cutter. This method is recommended similar to (a), which is performed in addition to the other methods. 4. Close-range photogrammetry was used to create a three-dimensional point cloud of the worn disc cutter. This method is the only one in this study that allows for the creation of a 3D model on which measurements and comparisons with other disc cutters can later be made. This method was also used to create a worn profile of the disc cutter ring and compare it with the original profile. On one hand, close-range photogrammetry requires a lot of time and specialized equipment, such as a suitable camera and computer equipment, but on the other hand, it offers the possibility of achieving the same results as the methods from (a) to (c). The assessment of  
Figure 16: A 3D model of an original (No. 1) disc cutter and a worn (No. 2) double disc cutter created based on the original and worn profiles with calculated volume and mass losses due to wear. wear achieved using the close-range photogrammetry method is consistent with the measurements from the other methods used in this study. Among the various methods for evaluating and measuring the wear of TBM disc cutters, the selection of a method depends on the required precision, the available measuring time and location, the accessible equipment, and the qualification of the measuring personnel. For a comprehensive investigation of the wear of disc cutters, several methods should be carried out simultaneously in order to achieve the best results. The measurement methods presented in this study have a significant impact on engineering applications. By integrating different techniques such as photogrammetry, caliper measurements, weighing, and visual inspection, engineers can develop proactive maintenance strategies, optimize cutting efficiency, perform comparative wear analyses under different geological conditions, validate numerical models, and explore innovative wear monitoring systems for disc cutters. Furthermore, these methods offer practical solutions for real-world applications, considering the amount of time they take, the equipment needed, and how well personnel can be trained.