Actually, harder rock is easier for tunnelling, either by classic blast and carry away method or by TBM.

There was indeed an area they did really fear, and which could have endangered the project. The German name is "Piora Mulde", a rock formation where the Dolomit has a sugary consistency. So, if you drill into that formation, the mountain leaks out through your bore… So, there was a considerable reserve put aside for those issues. Fortunately, they only touched that formation, and those few hundred meters did not cause too much delay.

I read that the main builders did not really make much money on the project. There was apparently a very strict control over change orders, and only things caused by geology, or changes caused by the customer were approved. However they say that "Gotthard Base Tunnel" is a boost in reputation, and it will eventually pay back.

So, AlpTransit, the managing company, did a pretty good job.

Yes, there were cost overruns. But the biggest reason for that was more and stricter safety regulations.

Ah, yeah, about 40 million Swiss Francs were "lost" because the Porta Alpina, a stop in the tunnel, under the Sedrun access shaft, was cancelled, because stopping there would have reduced the capacity of the tunnel by 30 or so percent. It would have been a novelty act, getting off in the middle of the tunnel and then taking an elevator up for 800 meters to get in the middle of a skiing area…

To the first paragraph of mook's message… every tunnel is a different beast. …and it helps to pay reverence to Sainte Barbara…