the "vanilla" TBM is an automated version of this: https://en.wikipedia.org/wiki/Tunnelling_shield#/media/File:Thames_tunnel_shield.png https://en.wikipedia.org

the "vanilla" TBM is an automated version of this: https://en.wikipedia.org/wiki/Tunnelling_shield#/media/File:Thames_tunnel_shield.png https://en.wikipedia.org/wiki/Tunnelling_shield#/media/File:... just with prepoured concrete blocks instead of bricks.