Re: Church Hill Tunnel

The last I heard, the work was stopped to allow the city engineer and other officials to evaluate whether draining the tunnel would cause it to collapse. A collapse of the tunnel could result in damage to structures and other features on the surface. This has occurred in the past on one or more occasions.
I understand that when the borehole broke into the tunnel, the leakage at the sealed portal increased, indicating that there had previously been a vacuum in the air space within the tunnel. So, previously, the water leakage had been impaired by the inability for air to vent into the tunnel. The borehole created an air vent that facilitated drainage. The natural conclusion is that the tunnel would have been more likely to collapse prior to the borehole, when the leaking water was pulling a vacuum. Therefore, pumping the water out the tunnel should not cause a cave-in, and subsequent surface damage. Furthermore, if, after exploration and possible recovery of the locomotive, the tunnel were left permanently vented, the vacuum would not redevelop.
It will be interesting to hear what the city decides about going ahead with the project. Proceeding with the project might prevent a future cave-in that may or may not occur. On the other hand, there is the, “Let sleeping dogs lie” principle that would suggest that any exploratory work on the tunnel might pose a unanticipated risk that would not occur otherwise. Indeed, it was an attempt to reopen and improve the tunnel that caused the legendary catastrophe that resulted in the buried work train. This infamous tunnel has been plagued by problems with unstable soil and groundwater conditions from the start.
RK