alt Hacker NewsIt's also really hard to make the tunnel remain a tunnel over its expected 150 year lifespan - given that it basically runs through a fault line. They had to study and test local geology for about 15 years, build certain sections to expect some movement over time, as well as kit everything out with a lot of sensors.
Overall an amazing achievement, and unsurprising it took this long to figure out!
After seeing some of the safety features in a short video I linked in another comment, I get the impression that this is either going to last much longer than 150 years or something so catastrophic will happen that nothing that could have been built would've persisted.