2 ms·My first thought is you would need to earthquake proof the heck out of a tunnel like that!by mikece 4y agoMy first thought is you would need to earthquake proof the heck out of a tunnel like that!zeristor 4y agoMine was more along the lines of how deep would the tunnel have to go.Arnt 4y agoAbout 200m, which is considerable but nowhere near a record, the deepest being 290m deep IIRC. It also doesn't have to be steep. 200m down in 10km is just a 2% incline.