> Regarding cost of mining solid rock: in fact, where I live, I think in the construction of underground train line, the actual cost of mining is pretty much of

> Regarding cost of mining solid rock: in fact, where I live, I think in the construction of underground train line, the actual cost of mining is pretty much offset by the price for sale of rock matter Any chance that you are living near https://en.wikipedia.org/wiki/Drammen_Spiral https://en.wikipedia.org/wiki/Drammen_Spiral ? I would have dismissed your claim as totally absurd had I not read about this gem of an improbable building project before!