http://www.carrtracks.com/tnl5343.htm
Why two bores? Why not one tunnel with two tracks?
Our DRGW addicts probably have the best…and correct…explanation. My guess would be grades inside the tunnels are different depending on prevailing direction of loads and/or grades leading into the tunnels on the opposite end are at different levels. At least those are the usual reasons
I’m going to guess that one tunnel was there and they needed two (tracks), so rather than shut one tunnel down for expansion they just drilled another.
John
Not a DRGW addict. My best guess would be that one bore was done with ‘Git-R-Done’ haste in the initial construction of the line as a single track route. When traffic density and construction monies became necessary and available, a second tunnel was bored. By boring a second tunnel traffic could still be maintained on the original tunnel during construction of the second tunnel.
Keeping the line open and hauling traffic is the name of the railroading game. To have enlarged the original bore to double track standards would have cause the original bore to have been shut down for at least signifigant portions of time to allow the construction crews to do their jobs. Much simpler and probably more economical to just bore a entirely new tunnel.
It’s also a lot easier to keep the roof up for a single track tunnel than one twice as wide.
A little searching for “Kyune” & “tunnels” & “D&RG” yielded results that indicate that the 2nd tunnel was probably drilled/ completed in 1913; the 1st one as part of the line’s original construction in the 1880’s (or so). A review of a detailed history of that line (which I haven’t done yet) will probably indicate that the 1st tunnel was simply was “developmental” = to get the railroad built; the 2nd tunnel was for additional capacity, just as the other posts above indicate. And unless the rock conditions are very favorable, a single-track tube or bore is preferable for structural reasons - they are more nearly circular than a double-track bore which would be elliptical, with its least-strong dimension in the horizontal plane, where the overburden load of the mountain above has its greatest effect.
Pretty much every situation I’ve seen with 2 tunnels above water, they were drilled at different times. There are a fair number of underwater tunnels that were done at the same time, though - the PRR’s under the Hudson (North) River about 100 years ago, and the English Channel Tunnel about 20 years ago are just 2 examples of those. There may be some exceptions over in Europe or Japan, but even if so, drilling 2 at once is only a recent practice.
As a practical matter, the best tool to drill a tunnel is another tunnel, with a railroad in it - even or esp. with a narrow-gauge industrial railroad. Even initial tunnel contractors will often drill a pilot tunel, either as part of the main bore or parallel to it, to accomplish that first. Then it’s a whole lot easier for removal of excavated/ waste rock and carrying in of the installation materials, plus equipment moving and supply, etc. Unless there’s some drastic time constraint to get 2 bores in service ASAP or an easy alternate route to the other side - both rare to non-existant conditions for most mainline U.S. railr
Because it is cheaper, faster, better in almost all cases.
Double-track tunnels are uncommon in North American railway practice because there are very few double-track railways built new in North America – almost all American railways were built as single track and later double-tracked. Double-tracking an existing single-track tunnel is anywhere from 100 times more expensive than building a second single-track tunnel because of the construction staging problem: How do you keep trains running through the tunnel while you enlarge it? Even without the staging problem, the cost of a double-track tunnel can be much greater than two single-track tunnels because the roof support problems are much larger in incompetent ground.
Examples of double-track tunnels in North America are almost entirely on new alignments built to replace an existing double-track or single-track alignment, where the construction staging problem went away because there weren’t any trains. The classic examples are the Magnolia Cut-Off on the B&O and the Bayshore Cut-Off on the SP; there’s also a lone double-track tunnel on Donner Pass dating to the Harriman improvements of post-1900. But for every one of those, there are dozens of paired single-track tunnels, e.g., Donner Pass; UP Weber and Echo Canyons; D&RGW Soldier Summit (example shown in this photo); UP Blue Mountains.
On Soldier Summit there are three paired tunnels – the two in the Price River Canyon are Nolan and Kyune (the pair shown), and the Thistle Tunnels. The original line was narrow-gauge laid 1881-1883. It went around these canyon ribs that Nolan and Kyune tunneled through. The line was standard-gauged single-track in 1890 at which time the first Nolan and Kyune Tunnels were drilled because
Another example is N&W’s new line through Elkhorn Mountain, which was constructed in the 1950’s. This line reduced the grade considerably, and made it possible for the N&W to retire its electric locomotives. I doubt that any of you non-N&W employees will have the opportunity, but I advise against passing an eastbound coal train engine in the tunnel, especially if you also are eastbound: the noise is more than deafening.
Johnny
Excepting the very long tunnels such as Moffat, most American railway tunnels in the 1860-1930 era were driven full-face without the pilot bore or pilot heading unless they were in extremely heavy ground. In poor ground sometimes the tunnel was driven with an upper face (the arch) advancing about 5-10 feet ahead of the bench (the straight part) because there was so much overbreak that this made it easier to crib the timber sets between the arch and the back before breaking out the tunnel to full face.
As an aside, most North American railway tunnels are essentially 100% self-supporting except within a few feet of the portals where there is heavily weathered rock. The rock forms a natural arch. Even siltstones and claystones so soft I can snap inch-thick pieces with the fingers of one hand, will often self-support for awhile, sometimes even a few decades, if you don’t mind a slow dribble of rubble falling off every now and then.
Tunnel lining, where it is used, is in almost all cases serving solely to support only the superficial rock. It keeps pieces of rock from gradually spalling off and falling onto the track as it weathers; that is, the lining is not supporting the mountain (except right at the portals, and then only a few feet worth). The same thing can be accomplished with rock bolts and shotcrete. With timber or steel sets, the idea is to keep the superficial rock snug up so that little cracks don’t slowly become big cracks and slabs of rock let go. The idea behind rock bolts is to tie the last few feet worth of rock into the mass. With both
Modern tunelling methods (tunnel boring machines like was used for the Thistle tunnels) increase the economic/technical advantages of two single tunnels over one double track tunnel. With a TBM; one double track tunnel approximates 4 times the material removed of one single track tunnel. And then you would have to almost half fill the tunnel with something - probably ballast - to get the track to the widest level of the bore.
The Hoosac Tunnel was built by the State of Mass. in the 1880’s. Later sold to the Fitchburg (B&M). It was and is a single bore with one track the first five or six years, and a second then added. The tunnel was later electrified. Electrics would pull the steam engines plus trains through the tunnel. My grandfather nearly died while riding a passenger train through the tunnel. The porter had neglected to close a passenger car window; smoke filled the car. I don’t recall ever seeing an article in Trains or elsewhere going into detail about this electrification. The catenary remained in place well into the forties.
Although M&K brought in a tunnel machine for the Thistle tunnels, the rock quality was such that the tunnels were drilled using conventional techniques. There was no shortage of labor around as the coal mines in the area were mostly shut down until the tunnel was opened. The first train went through within hours of holing through as the tunnel was dug full size. Then M&K made DRGW an offer they could not refuse for the second bore. The second bore was also drilled using conventional techniques, but was fully lined before use. Then traffic was diverted to the second bore while the rough bore #1 was lined and the track brought up to mainline standards.
For information on the Hoosac Tunnel, you can check www.hoosactunnel.net It gives the history of the construction and much more information ( I barely looked at the site before posting this).
Johnny
There’s a nice write-up in Middleton’s When the Steam Railroads Electrified, both the original Kalmbach edition and the Indiana University edition. There’s also a short article in CERA’s bulletin #118, Westinghouse Electric Railway Transportation.
LV’s original tunnel under Musconetcong Mountain at Bellewood (now Pattenberg), NJ, was doubletracked. Later reduced to single track to accommodate modernized equipment size in the 1920s, then replaced by a larger, adjacent doubletracked tunnel. (To see the original tunnel now, it’s hard to imagine anything of reasonable size could have fit through there on two parallel tracks.)
State Line Tunnels just west of the NY/MASS border had two tracks in the original north bore (1840s) and two more in the subsequent south bore (1912), both later single tracked to accommodate modern equipment and the north bore eventually taken out of service.
Then there are those dual tunnels along the east shore of the Hudson River which at one time had doubletracked tunnel next to doubletracked tunnel as well as doubletracked tunnel next to single-tracked tunnel.
And let’s not forget the doubletracked Sand Patch Tunnel which replaced B&O’s original single-track tunnel under the Alleghenies, Otisville Tunnel which replaced Erie’s original line which looped up and over the Shawangunk Mountains, and other lesser-known doubletracked tunnels such as the LV’s Rockport Tunnel in the Lehigh Gorge.
There’s also a double-track tunnel - about 3,000 ft. long as I recall, when we hiked through it about 40+ years ago - to the south (railroad east) of the Tunkhannock Viaduct at Nicholson, Penn. on the former DL&W - now CP. But that one was also drilled as part of the separate project for the realignment and improvements early in the 20th century, not “under traffic”.
- PDN.
EDIT: Scaled and taken from Google Maps: About 3,500 ft. long; about 2 miles south of town = intersection of U.S. 11 = Lackawanna Trail with PA 92 = Bacon St. and Grand Army of the Republic Highway. The NW portal is about 1/4 mile SE of Rt. 11 along the “Abington and Waterford Turnpike Rd.”, down the hill on the NE side. For the SE portal, continue SE on the Turnpike Rd. about another 1/2 mile (it may turn into “College Ave.”) to Tunnel Rd. on the NE side; go NE about 0.1 mile, and the portal will be down the hill a ways on the right = SE side, before the intersection with Spencer Hill Rd.
There is another reason for two single bores (sometimes with a pilot bore in between) in modern tunneling practice (such as the Gotthard base level tunnel, and the Channel tunnel): safety. If you have two bores side by side, say a few metres apart, you can (and do) have interconnecting little tunnels between them, with fire doors on them. Then is something goes seriously wrong in one bore – say a truck on a flat car catches fire (it’s happened) or something like that – it is possible for all and sundry in the one bore to go to one of the cross connecting tunnels and get into the other tunnel or the pilot bore (left open for that reason), close the fire door, and wait for the cavalry to show up…
You’re referrring to Factoryville Tunnel (aka Nicholson Tunnel). DL&W’s original single-track tunnel through that mountain was completed 1854. A second, parallel, single-track tunnel was completed 1883. Both were replaced by the current double-track tunnel in 1915, which has since been reduced to single track. I rode an NYS&W business special through there about 20 years ago, and the dome car enabled a great view of the cavernous ventilation shaft(s) which rose up through the tunnel ceiling to the surface. It’s one of several double-tracked tunnels the DL&W built during a period when certain American railroads were emulating the high engineering standards of their better-financed European counterparts.
Also note there are two different alignments…the old pair about a mile from the new tunnel and about a hundred feet in elevation, too
Bruce, for a western guy you have a surprising - and embarassingly ! - good knowledge of eastern railroad tunnels.
Your reference to the Hudson River tunnels had me puzzled for a little while - then I figured out you probably meant the Cold Spring, NY tunnels, which are actually about 2 miles north of that town, on the former NYC main line, and about 500 ft. long. (Cold Spring is basically on the other side of the Hudson River and about 2 or 3 miles north from the U.S. Military Academy at West Point.)
There appear to be a similar tunnel(s ?) about 350 or 400 ft. long, 5 or 6 miles further south (south of Manitou) under the Bear Mountain Bridge (U.S. Routes 6 and 202) across the Hudson Rive