Tunnel hole-through
Tunnel hole-through, also called breakthrough, is the time, during the construction of a tunnel built from both ends, when the ends meet, and the accuracy of the survey work becomes evident. Many tunnels report breakthroughs with an error of only a few inches, for example:
- the 1858 Blue Ridge Tunnel –
- the 1944 Blue Ridge Tunnel replacement – - 1944
- the Lötschberg Base Tunnel – 10 cm
- the Holland Tunnel - 1 cm