Analyses of rock failure mechanisms beneath disc cutters are presented. Full-scale cutting tests are conducted to assess the global energy input in comparison with rock chips and excavated volume. Small-scale cutting tests are subsequently used for macro-and microscopic analyses of rupture modes and crack propagation. A high spatial resolution allows to obtain pictures of crack networks in different rock types. It is shown that all specimens develop lateral cracks in sufficiently confined areas whereas median cracks typically develop in boundary regions. Regarding cutting forces, a hypothesis is proposed that associates sudden force drops accompanied by sudden sound emission with grain crushing in the proximity of the cutter tip.
The loading on the tools of a TBM can usually only be estimated through the global thrust force, which gives a typical force of about 250 kN for 17′′ discs. The actual loading is however highly variable, with peak loads that can be many times the nominal load. In the present paper the development and implementation of a method is presented, which makes it possible to measure disc forces in-situ and in real time. It turns out that the measured forces are unevenly distributed over the area of the face and can be correlated with geological/geotechnical features in the face. Furthermore, a method is presented which makes it possible to document the face photographically. Single images or videos are combined to an overall image by means of digital image processing. The quality of the pictures obtained in this way can provide a significant improvement of the geological documentation of TBM drives.
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