In 1856 the almost one mile long Afton Mountain or Blue Ridge Tunnel was completed. The chief engineer, Crozet, tunneled from both sides of the Blue Ridge Mountains. When the two tunnels met, they were 6 inches off perfect alignment. In 1944 the C&O bore a new tunnel parallel to the Blue Ridge Tunnel. It was a bit longer than its older brother, but it was also four feet off perfect alignment when the two tunnels met!
So much for progress. ;D
Gene
that happened a long time ago. what is your point?
lex
Uh, math time. Which is greater, 2009-1944 or 1944-1856? BTW, I was alive in 1944 and I'm not sure it is THAT long ago.
Gene
I guess I must be ancient too, Gene. I can remember 1944. Surveying equipment at the end of WWII was much advanced compared to a hundred years earlier. On the other hand, the continent was survey from coast to coast with optical equipment back in the 1800's. I suspect the difference in the tunnels are largely due to lack of fully trained and experienced personnel. I understand that during the war, many surveyors ended up directing artillery fire, a job which requires accurate measurements and precise calculations similar to those used in surveying. Amazing how they were able to make the measurements and do the calculations quickly and accurately under pressure and without a computer. They must have been supermen to do that a long time ago.
Jim
Hey, Jim, I'm an artilleryman - though retired now. We love our survey guys, but most of them we train ourselves. While an arty surveyer can adjust fire, he has far more important things to do - like surveying battery centers, radar sites, observation points, etc. Then there are the engineer surveyers - and I imagine the engineers train their own, too.
BTW, I had staff responsibility for survey several times - including times when it was for real. :D
Gene
Keep in mind that back in those days they didn't have the hyper accurate geographical maps that we have now. Nor did they have the aid of GPS. Now when two crews line up to dig out a tunnel from both ends they check their position with GPS then lock in the position they want to be at when they reach the rendezvous point with the other team, align their directional lasers and off they go. Even with all that they can still be off by more than 6 inches.
I would say the fact that the tunnels meet in the middle at all is a great accomplishment especially given the length of some of them.
NM
For some information on a rail construction project, including 16km of tunnelling, taking place here in Johannesburg have a look at this site.
http://www.gautrain.co.za/index.php?fid=1&fp=0
Dave