Complex sentence: At one point the excavated dirt from one of the tunnels collapsed part of the ceiling in a camp building where it was being hidden, however the camp guards, aware of the ruse, did not stop the project.
Split into simpler sentences: At one point the excavated dirt from one of the tunnels collapsed part of the ceiling in a camp building where it was being hidden. The camp guards, aware of the ruse, did not stop the project.