Tunnel hole-through

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Dismantling the tunnel boring machine 10 days after the hole-through on the Gotthard Base Tunnel in Switzerland.

Tunnel hole-through 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 — indeed, it is hard to think of one much worse than this.^{[citation needed]}