How to do a wide portal for a tunnel through a mountain? May 17-All Done.

Hi Alex, a four track portal sounds like it would look neat. If the tracks are on a straight section then I would build the portal as one opening. But, to give it a true look try placing a buttress in the middel of the four lines holding up the portal overhead lintel.

Make the buttress, or center pire  3/4 of an inch wide and let it run into the tunnel for a foot or so. You can even make then a series of 3/4 inch square columns that run up the center of the tracks. These columns work best on turns. This is the system they use on most subways. 

Hey, Mario –

Here are pictures that show my dilemma. The track spacing is 4-1/2” and if I put anything between them, the clearance to that object will be less than the recommended 9 feet (full scale) or 2-1/4” from the center of the track to the obstacle.

The first picture shows a 3/4" wide column (3-feet) as you suggested. I wouldn’t mind that, but the clearance now us about 1-1/8” from the outer rails, and I don’t know if that would be a problem. I believe it would clear most engines and rolling stock, but I don’t know.

Also, where the temporary arch and column are in the first picture is not where they really need to be. The second picture shows where I really would like to have the portal, and it being right over the turnouts presents yet another problem.

Where the portal needs to be -

This third picture is from a distance, to show where the Hidden Pass Mountain will be – behind the stairwell – hence the ‘hidden’ name. 

I am just trying to come up with something that looks somewhat realistic.

Thanks for your help!!!

Alex

Can you use something to simulate steel?

Steve C.

Alex....

This is just an "architect's" viewpoint so take it for what it is worth (perhaps not much).  As you and I have discussed recently, stonework for long spans, while it looks nice, would not work unless steel was involved along the bottom of the stone course at the top of the portal opening.  You could simulate something like that and it would be fine.  Mario's idea is perfect but it appears you will have a problem using that method.  Steve's idea may be your best bet perhaps with a highway modeled above the girder with the trains going under and beyond the girder disguising the entrance to the tunnel.  Anyway...here are a few pictures that may help that I found on the web....notice that if you simulate concrete formed and poured work (smooth), you can get away with a flat topped portal since steel reinforcement would be within the concrete work....

Alan

I carved mine from blue foam.

Something realistic?

I've never seen a tunnel (meaning drill-and-blast or bored) wider than two tracks. The Park Ave portal in your group of pics is a trench that was roofed over between street overpasses. Even then the outer tracks travel in their own single-track space.

A cut-and-cover tunnel can be four tracks. New York City is fairly riddled with them. But even the ones that transition to bored tunnels become a pair of tubes side by side, or a single bi-level bore with two tracks on each level.

Toy train tunnels with 3, 4 or more tracks going through a "mountain" with a single opening just don't look realistic since real-life rock doesn't have the tensile strength for an opening that wide. In your case, I'd either try to make twin two-track portals at both ends, or have something man-made over the tracks that looks like it was built after the railroad.

---PCJ

Alex,  I agree with the observations offered by everyone above. The tunnel builders would be even more concerned with the support of the wide span of the tunnel roof than just the portal itself.  For this reason two separate tubes, i.e. two independent tunnels, are normally constructed as the solution for circumstances requiring a high tunnel capacity. Some sort of a partition between pairs of tracks would be normal and for masonry tunnels almost essential. Railroads often reduced their trackage at the approach to a tunnel and lived with reduced capacity. A masonry portal would look realistic if you could include an intermediate support. That would probably require the portal to be moved out away from the crossover as well as more separation between tracks two and three. A reinforced concrete portal or steel bridge would be the most realistic solutions if an intermediate support is not acceptable.  But, all this having been said, remember the motto of the operators of the Twin Lakes Refinery.  Pat B.

Hi Alex, I see what you are saying about the center column. With the cross over switches you may have a problem with over hang when the big steamers need to change track.

As stated above the only way to do a four track underpass and make it look real is to do the overhead lintel out of steel and then we are back to looking less then real.

Is it possible to move the two inner lines over about a foot or so and build the portals as two double tunnels fifty scale feet apart. I don't remember ever seeing such a tunnel in the real world but this is a toy train layout and a certain amount of belief compromise is expected.

Move the switches to this location and it will allow for double portal of tunnel

Hey, guys

Lots of good advice and food for thought, and I really thank you all.

First off, I had not planned a mountain or tunnel(s) in this section. It was an afterthought after I named the railroad. I came up with the name Hidden Pass Junction Railroad (HPJ RR) due to the fact that the stairwell divides the layout into two sections, and these are joined behind the stairwell. This area cannot be seen except from the service aisle, so it is sort of hidden, and hence the name.

After the railroad became the HPJ RR, I thought it would be neat to add a mountain and really make the junction hidden. BTW, the mountain will not have sides, so the track and turnouts will still be easily accessible from the service aisle side and from the stairwell closet.

Steve, PRRfan –

Yes, those most definitely are good options, and I have some already on the layout. I was looking for something a little different this time.

This picture shows where I have used the more standard portals, and I will have two more on this side, on the upper level. The red line shows where the mountain will be as seen from the west side. The wide portal will be on the east side.

Elsewhere I have three simulated steel beam portals like this one.

PCJ, Pat B. –

I fully appreciate your points, and that is what concerned me. But, since we this is our make-believe world, I’ll bend the engineering and physical principles, and compromise.

Following, Alan’s suggestions, and hoping to please engineers and architects, I will follow ancient Roman and other engineers of antiquity and make good use of the ‘arch’.

To keep the clearances as close as possible to the real-world specifications, I drew the track I have, the necessary clearances, and then resorted to an ellipse shape arch, as follows:

(FOR SOME REASON IT TOOK ME ABOUT AN HOUR TO LOAD THE NEXT PICTURES)

Hey Alan - remember how to draw an ellipse with a string?

Cut with a band saw - -

Added some paint - -

And ready to blend in - -

Thanks to one and all!

Alex

PS.

Mario, Nelson - I just read your posts.

Actually, at this point it would be difficult to make changes to the track layout; I more or less have to live with what I have. But I do thank you!

Looks great Alex.

Alex.....wonderful compromise!!  Your solution is ingenious!  AND....it is plausible especially if the inside of the tunnel is supported by concrete/steel structure to which PCJ was referring.  AH...YES, I do remember those days of drawing ellipses with strings!!..almost forgot about that....  Anyway, very nice way of solving your problem and in this case the portal looks like a concrete pour that has some architectural flair...very nice..

Alan

Alex,  Ths eliptical portal has much more style and credibility than the flat concrete portal.  Looks great.  Pat B.

I like that .  Keep in mind a lot of tunnels got "day lighted"

Thank you! I am glad you guys liked the elliptical shape also. Here is how it looks now.

I posted more pictures under my layout thread, below.

Thanks for your help!

Alex

Alex...turned out great!!!  Are you going to do something similar on the other side??

Alan

That came out great!

Doug

All's well that ends well.

Alex, it looks great.  I have spent the last 3 years in the tunnels on the CSX National Gaterway ang it does look protypical. If you can make sure to show drainage and a dark interior.

Also my wife likes the mountain and portal.

Alan,

Yes, except that the portals on the west side will be easier to make. My idea is to build another 'mountain shell' (if we can call them that), similar to the one I just finished on the east side, and sort of bridge their tops, which may be the only part that can be seen. I won't be able to start on this for a couple of days, but I'll post pictures . . . soon.

Mario,

Thx! (. . . and good beginnings usually lead to good ends

Lou,

That is good to know. I strive to try to make as many things as possible to look prototypical, but I am 'shooting in the dark' most of the time. That's why I post so many questions . I'll pursue your suggestions.

Oh, and your second post - - -  That is especially good to know!

Thanks!

Alex