Tunneling through the alps isn't exactly easy, it's actually harder than through a normal sediment. Well, maybe cost wise a weak sediment may be more expensive

Tunneling through the alps isn't exactly easy, it's actually harder than through a normal sediment. Well, maybe cost wise a weak sediment may be more expensive (but not by a factor of 20x, more like 1.5-2x), but vertical rock formations bring all kinds of surprises, which leads to accidents including deaths, which leads to insurance premiums. To illustrate, here's a normal sediment: ----------------- 20y ----------------- 100y ---------------- .... here are the alps: | 10M years | 10.1M years | 12M years | .... Edit: You can also compare to the other link I posted in a sister comment, about a new tunnel through one of Zurich's hills. That project was actually less expensive per km than the Gotthard base tunnel, so I don't think the rock is the problem.