Complex sentence: In June 2010, one of the TBMs completed its tunnel at the cavern; the second TBM broke through the wall of the cavern on July 15,2010, completing its tunneling operation.
Split into simpler sentences: In June 2010, one of the TBMs completed its tunnel at the cavern. The second TBM broke through the wall of the cavern on July 15,2010, completing its tunneling operation.