Here is a very interesting video of the challenges of digging a new pump station tunnel at a steep angle and all the unknown difficulties that can show up.
+1 for that video. I've discovered it accidentally and was blown away. Then I watched the other videos by Marti Group and was continued to be impressed. Unfortunately they don't have many videos on YT (there are not many projects of that size I guess)
https://youtu.be/6AV2NcyX7pk?si=cGvHD4eUp6zQSef2