There have been plenty to cases where these things have broken down which caused years of delays and usually another tunnel had to be dug to get them free, some

There have been plenty to cases where these things have broken down which caused years of delays and usually another tunnel had to be dug to get them free, sometimes they changed the path of the original tunnel to circumvent them where it was possible and more cost effective. These machines are constantly serviced and aren’t operated one minute past their life spans. I really don’t think you understand how many hours these things operate for.... To put things into perspective machines have a single digit meters per hours top speed and not high single digits to boot, and if you are digging in rock you are looking at sub meter per hour figures. If you have a source to contradict this I’ll be happy to read it but honestly every source from articles to documentaries pretty much paints the same picture these machines aren’t worth their weight in scrap once they are done with.