"Preedy said that when Bertha was being built in Japan, one of the tests performed was to turn on the motors and rotate the cutter head. That’s when testers heard a noise and took Bertha apart. They found that some parts of the machine weren’t moving properly and caused “some metal-on-metal contact and basically damaged the seal assembly for the main bearing,” Preedy said."
This was a manufacturing problem discovered when it was first spun up in a test, as far as I can tell not even involving any digging, just making sure everything functioned correctly (e.g. what NASA didn't do with the Hubble mirror).
"Preedy said that when Bertha was being built in Japan, one of the tests performed was to turn on the motors and rotate the cutter head. That’s when testers heard a noise and took Bertha apart. They found that some parts of the machine weren’t moving properly and caused “some metal-on-metal contact and basically damaged the seal assembly for the main bearing,” Preedy said."
This was a manufacturing problem discovered when it was first spun up in a test, as far as I can tell not even involving any digging, just making sure everything functioned correctly (e.g. what NASA didn't do with the Hubble mirror).