Maybe I am wanting to self-flagellate myself because when I realzed that I had enough terrain area in the route to extend the NS line almost 9 miles further north, I decided to just do it. Once I get this route done, that area of the NS, which will then extend from mile 19 to mile 54 will be copied into my planned Appalachian Sub. route, but there is one huge problem. Natural Tunnel sits between mile 24 & 25. Aerials from Google Earth distort the track terribly so I am taking measurements as best as I can from the track chart. From north to south, the tunnel is entered on 2 degree right curve which compounds to a 17.7 degree (99.7 meter radius) right curve and then with no tangent between, it switches to a 7.5 degree left curve before passing through a short man-made tunnel on a tangent. This is now a Virginia State park and there is a chair lift which you can ride down to track level. While you can't go in the tunnel, you can get real close. Look it up on the Internet. I may not have the skill to decently replicate the big tunnel, so I may just leave the terrain untouched and maybe someone with more terrain skill than me can do it. The tunnel was formed by Stock Creek over millions of years and we know from legend that it formed a easy path through the ridge it goes through for Native Americans in the long ago. It was also on the route that Daniel Boone used to go to Kentucky from NC. The South & Western railroad built through it around 1890 and that road became part of the Southern a few years later. I've spent many hours INSIDE that tunnel measuring rail forces when I worked for the SR and I will tell you that it gets CROWDED when a train goes through it. And I have been through it around 100 times as well on coal trains. Both NS & CSX use it now thanks to reciprocal agreements from around 1982, and the line is signalled. It was dark territory when I worked there, 1965-1978. Here is a link to the website. http://www.dcr.virginia.gov › state_parks › nat.shtml It also has i t's own "lovers leap" legend, said to be true. A native american girl was in love with a lad from another tribe. I would guess she was probably Cherokee, he could have been Shawnee. Daddy said NO to the girl, so she jumped from the highest point of the rim over the tunnel opening, about 275 feet to her death.
The big (south) opening measures over 100 feet wide by 70 feet or so vertical, and then there is a sheer wall above it for over 200 NAT_TUNNEL.jpg feet. That end has not been altered but the small opening (north) was enlarged a little around 1980 when curvature was eased from 19 degrees to 17.7 degrees on the sharpest curve.
See the attached image. Working from the south (to the left) upward at a 1.5% gradient, there is a short tangent through the "Little Tunnel" which was man-made. Since it has natural rock portals, I'll use round tunnel sections as those seem to match natural portals better. To be absolutely correct the interior walls would have to also appear to be natural. Notice that for a short distance the red highlited section is "hanging". There is a short plate girder span starting about 5 feet outside the tunnel. At about mid-point of the red section, there will be a 7.5 degree curve to the right and once inside the natural or "big" tunnel, there will be a 17.7 degree curve to the left for a ways, followed by a compound to 2 degrees to the left. I will probably use a 250 meter radius for the 7.5 degree but I will have to use dynamic for the 17.7. Today there are a lot of walkways & protective items so that tourists can see the tunnel and be warned when a train is coming. There are not many, probably no more than 4 trains a day. One thing that has been done is to extend the viewing area about 75 feet inside the tunnel and in my experience from that point, you can see light from the north entrance, but it is still 800 feet or so away.
Jerry
The big (south) opening measures over 100 feet wide by 70 feet or so vertical, and then there is a sheer wall above it for over 200 NAT_TUNNEL.jpg feet. That end has not been altered but the small opening (north) was enlarged a little around 1980 when curvature was eased from 19 degrees to 17.7 degrees on the sharpest curve.
See the attached image. Working from the south (to the left) upward at a 1.5% gradient, there is a short tangent through the "Little Tunnel" which was man-made. Since it has natural rock portals, I'll use round tunnel sections as those seem to match natural portals better. To be absolutely correct the interior walls would have to also appear to be natural. Notice that for a short distance the red highlited section is "hanging". There is a short plate girder span starting about 5 feet outside the tunnel. At about mid-point of the red section, there will be a 7.5 degree curve to the right and once inside the natural or "big" tunnel, there will be a 17.7 degree curve to the left for a ways, followed by a compound to 2 degrees to the left. I will probably use a 250 meter radius for the 7.5 degree but I will have to use dynamic for the 17.7. Today there are a lot of walkways & protective items so that tourists can see the tunnel and be warned when a train is coming. There are not many, probably no more than 4 trains a day. One thing that has been done is to extend the viewing area about 75 feet inside the tunnel and in my experience from that point, you can see light from the north entrance, but it is still 800 feet or so away.
Jerry
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