I don't understand the secrecy about the cause of this closure.
Having to close these roads while the TBM transits the area could mean that they've unexpectedly encountered some very poor ground conditions (a patch of very loosely compacted sand for example) which could result in subsidence at ground level when they cut through below. That should be easy to explain to the public. With tunnelling the only way to fully understand ground conditions along the route is to dig the tunnel, prior to that you only know the condition where you drilled boreholes.