Even Deming commented that his principles couldn’t catch everything, especially when it came to maintenance. Other thing is that with a tunnel, you can’t inspect everything you’d want to, and this tunnel was on the older side.
Most tunnels are a shell with an outer shell to accommodate ventilation and maintenance access, as well as to offer more rigidity with less material. What bothers me here is that usually such elements of critical infrastructure get an inspection after an earthquake. One might expect a "wounded" structure to fail in a succeeding event, but one would think the inspection sufficient to determine safe operating conditions under a static load given the usual safety factors.
This is just weird.