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 – 6 inches (150 mm)
• the 1944 Blue Ridge Tunnel replacement – 4 feet (1.2 m) - 1944
• the Lötschberg Base Tunnel – 10 cm
• the Holland Tunnel - 1 cm

• Cascade Tunnel
• Siloam inscription

• Gautrain tunnel breakthrough
• Brisbane Clem 7
• Gotthard tunnel
• Lotschberg - 10 cm