A tunnel boring machine doesn't cut rock. Its 66 steel discs roll, and the rock breaks between them. This episode takes the Gotthard Base Tunnel machine apart: why the cutters roll, how a cutterhead the size of a house turns, how the machine pushes on a mountain without sliding back, the one detail that tells you when a disc is finished, what changes when the ground can't hold itself up, and how the tunnel lining is built while the machine digs.

Chapters

0:00 Hook: wheels that roll

0:30 Map: one metre of tunnel

1:02 Sheet 1: Tools that don't cut

3:12 Sheet 2: A wheel the size of a house

4:18 Sheet 3: Pushing on a mountain

5:38 Sheet 4: Witness Mark: the edge of the ring

7:04 Sheet 5: When the ground can't hold you

8:50 Sheet 6: Building the tunnel as you dig

9:45 Answer: how granite gives way

10:35 Question for TBM crews

Sources

1. Herrenknecht AG, "Gotthard Sissi: cutterhead as a witness in the Swiss Museum of Transport": https://herrenknecht.com/en/newsroom/pressreleasedetail/gotthard-sissi-cutterhead-as-a-witness-in-the-swiss-museum-of-transport

2. Zare Naghadehi & Mikaeil (2017), "Optimization of TBM Disc Cutter Spacing in Jointed Hard Rock...", Periodica Polytechnica Civil Engineering 61(1), doi:10.3311/PPci.9521

3. ITA-AITES, "EPB shield": https://tunnel.ita-aites.org/en/how-to-go-underground/construction-methods/mechanized-tunnelling/epbs-shield

4. City Rail Link Ltd, "Our TBM explained": https://www.cityraillink.co.nz/newsletter-june-2021/our-tbm-explained

5. Amberg Engineering, "AFER visit: Gotthard Base Tunnel" (Faido): https://amberggroup.com/fileadmin/amberg-group/documents/projects/gotthard_base_tunnel/AFER_Visit_-_1_PP_Gotthard.pdf

6. ITA-AITES, "Slurry shield": https://tunnel.ita-aites.org/en/how-to-go-underground/construction-methods/mechanized-tunnelling/slurry-shield

7. Tunnelbuilder, "China deploys underwater space station to overcome hyperbaric TBM challenge on Jintang subsea tunnel"

8. Tunneling Online, "TBM hyperbaric intervention": https://tunnelingonline.com/tbm-hyperbaric-intervention/

9. Janc, Vizintin & Pal (2024), "Investigation of disc cutter wear in TBMs", Applied Sciences 14(6), 2443: https://www.mdpi.com/2076-3417/14/6/2443

10. Rostami & Ozdemir (1993), "A new model for performance prediction of hard rock TBMs", RETC Proceedings; Rostami (1997), PhD thesis, Colorado School of Mines (CSM model: disc tip width vs penetration).

Numbers marked "derived" on screen are our own calculations from these sources.

Corrections go in the pinned comment.

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How this video is made: script researched and written with AI assistance, narrated by a synthetic voice, animations generated from code. Technical content reviewed by a human engineer. Sources are listed above; corrections are pinned in the comments.