The trench option includes a new and unusual feature — one that could pose unacceptable risk to the construction workers.
CSX needs to maintain two tracks in operation — after all this is a two to four year project and they have a business to run. In other projects, such the Alameda trench the existing rail system was kept in operation while the trench was being dug. Hence operations were not affected during the construction phase. (It would see the same were the western bypass to be selected — CSX would run trains in the normal manner on the existing tracks. They would then connect the new and the old tracks in a very short period of time.)
However, given that CSX is not able to build a third, temporary track through Ashland they have proposed that a temporary wall be placed longitudinally along the trench. There would be fill on one side of the wall, with two tracks on it. The other side would consist of the gradually growing trench.
When digging trenches for pipelines, if there is not sufficient space for sloping walls construction managers often make use of a trench box — as shown in the picture at the top of this post. In our case the box would be enormous and would have to have cross supports stretching all the way across the digging area. It is difficult to visualize how this can be done safely. And the box would have to grow down as the trench became deeper.
Note: A trench box is no good at all if, as shown in the picture, workers don’t use it.