# Tunnel building - what about furnace duct work?



## jimtyp (Jan 2, 2008)

I'm going to be building a tunnel for my layout. I'm thinking about 8' to 10' long. Straight through. I've seen lots of good ideas on MLS; flue liner, concrete blocks covered in pond liner, PVC pipe, poured concrete, etc. One option I was considering is furnace duct work. Anyone have any experience with this? Would it rust quickly?


----------



## Dean Whipple (Jan 2, 2008)

Would it rust quickly? probably..... 
Also you may want to consider having an access hole or making it shorter....because you will have a derailment at some time or another, and unless you have really long arms it'll be hard to fish it out without damaging your rolling stock.


----------



## John J (Dec 29, 2007)

Length should be twice the length of your reach/ arm. That way you could reach and car from either end. 

Make it tall. You can always hide the height with the portal. 

I am the one who made the 480 LB single pour tunnel it is 10 inches tall 

It was a experiment that went south. A little over kill 

I will do a single pour again just not that heavy 

What ever you do I would make the floor a concrete slab. 

Slope it a little or make it so Water can drain out. 

If you get a leak in it is really that bad? Real tunnels weep water 

JJ


----------



## R.W. Marty (Jan 2, 2008)

Ductwork called "furnace Pipe" or "KD" for the knock down snap seam used is usually light gauge, yes heavier can be made or bought if you can find it. Pipe in a size big enough for tunnels in G scale, 12-14 inch, would not withstand the burial without deforming or collapse. A better approach would be to use a commercial pipe called "spiral duct" this can be obtained in 10 foot lengths no problem and in a gauge heavy enough to withstand the pressure from direct burial or concrete encasement. Or go all out and use corrugated culvert pipe in metal or plastic. 
In a 10 foot tunnel at least 2 access hatches are needed.


----------



## cape cod Todd (Jan 3, 2008)

I have 5 tunnels 3 are made out of 12x12 flue liner, I have a 2', a 4' and a 6'. My first tunnel is made out of plywood and is more or less a box shaped like a "J" about 8' long. That one has a access hatch. My long tunnel is built around a 5' diameter curve in horseshoe shape using cinder blocks for sides, gravel for the roadbed and plywood wrapped in plastic for the roof. I'd recommend Johns idea of a concrete floor since a critter got into my tunnel one time and dug all around the edges and buried the track. I had to vacuum it out through the entrances and the 2 hatches I built in. if you are track powered avoid breaks inside the tunnel or use clamps or soldered jumper wires. if your RR has problems like derailments guess what they will be in the tunnel. In retrospect I would have done 3 hatches in the 15' tunnel, the less you need ot reach in the better. The last thing you want to do is have to use a broom handle to push your derailed fine loco out. 
Good luck


----------



## mickey (Jan 28, 2009)

Personally, I'd be worried about longevity and not collapsing, depending on weight on it. I used the plastic ribbed culvert pipe which can bend in you want. Here are pics of mine in stages, with the final one as it looks today with onions growing on top. I do not have any water issues at all and it has been in place for several years and many rain events. Since I was going through a rock wall, I anchored the ends with metal brackets and then made a cement collar to prevent drips on the ends. So far so good. It is approx 10 feet long with an access port in the middle, which I have only used a coupe times, but very glad it was there.


----------



## jimtyp (Jan 2, 2008)

Great info guys! I hadn't thought about the drainage, so will keep that in mind. I'll also check into the spiral duct, hadn't heard of that one before. 

Question, it seems like if you use PVC pipe, blocks, concrete, flue liners, etc. they are all solid. But yet it sounds like "access" is essential, but how do you build those?


----------



## mickey (Jan 28, 2009)

I did not happen to take a pic of the access construction, but I used another piece of the same pipe and cut a saddle. The same process that welders do when making pipe fences. I cut a round hole in the existing pipe a little smaller than the inside dimension of the pipe. Then cut a length that is the total height I want to end up with, plus over half the total diameter of the pipe. You cut a U shape in both sides of one end, creating a saddle, just like the part that goes on a horse. That way it straddles the pipe over the hole you cut, then I screwed the flaps onto the main pipe with stainless screws. Over half was so when I screwed the flaps, I could get the a little wrapped around the main pipe just to give it a little extra strength due to the dirt I was adding. Then I just set the sprinkler system access box on top of the pipe. 

At least that is how I did mine.


----------



## jimtyp (Jan 2, 2008)

sprinkler access box is a great idea


----------



## astrayelmgod (Jan 2, 2008)

I have a tunnel that is about 15 feet long. No access hatches, but it is big enough to crawl into. Only one end is visible, the portal at that end is normal size, the tunnel itself, including the far portal that no one can see, is about two feet high and wide. It works, but if I had it to do over, I wouldn't. I would have it disappear by going behind, not inside, a mountain. 

In addition to a broom handle, I also use a "rescue train", an NW2 cow and calf (lots of motors, and scads of pickups for track power) to push stalled trains out of the tunnel. I only have to get into it about twice a year, but that is plenty. 

I second having a concrete floor if you have a wide bottom. I had a mole, or some other varmint, that used the tunnel as a dump for his extra dirt. The critter filled a five foot long section completely full of dirt, floor to ceiling. 

Also, if you have a thing about spiders, forget this idea. Here in So. Cal, black widows love to make a home in the tunnel. Dunno what they eat, as I never see any flies in it, but the spiders keep moving in. We don't have snakes here; so I've never had to worry about that.


----------



## Dave Meashey (Jan 2, 2008)

Snakes, Spiders, and Moles, Oh MY!!

You make me feel lucky.







My worst critter problem outdoors was with squirrels. One squirrel filled up the mine entrance with acorns. Another squirrel decided the miner's pack donkey was good to gnaw upon. Since the donkey was a lead casting, that problem took care of itself!










Best,
David Meashey


----------



## mickey (Jan 28, 2009)

I've already thought about the spiders,etc. I've mounted a propane torch on the front of a flatbed car, a camping bottle on another one and push it through in front of the engine like you would a snow blower. It burns up any cob webs and slow moving things. I wait at the other end of the tunnel and get 'em with the shot gun as they come running and slithering out. Works great but wife says its just a little weird.


----------



## docwatsonva (Jan 2, 2008)

A few years ago when I was building my layout, I installed a 7 ft. curved tunnel. It was built using concrete pavers and bricks. Here are a few photos of my tunnel.


Before I built my small mtn., I dug the trough, laid in some crusher fines to serve as a base and leveled it with a slight slope to the left for drainage. I next laid in the pavers and filled in the pie shaped gaps with concrete. 











I next built the walls using the concrete bricks. The bricks are glued together with PL concrete adhesive. I also used concrete crack filler to help seal the bricks against water penetration. You may also notice that the track was curved to fit and installed prior to adding the roof. More concrete pavers were used for the roof. What is not shown is the fact that the the guy who was doing the tile work for our new home took an interest in the project and volunteered to cut the roof pieces to fit the curve. He did such a great job that there were no gaps greater than a 1/16 " in the ceiling.l











After the structure was completed, I wrapped the entire top and sides of the tunnel with a couple layers of heavy duty plastic and filled in the sides with stones before covering with dirt. 












Here's what it looks like now. The portals are made from concrete castings using Jig Stones molds. BTW, I cut some plugs from 1" blue styrofoam to use to close off the openings when not in use.












Hope some of this infomation helps in your upcoming project.

Doc


----------



## jimtyp (Jan 2, 2008)

Awesome tunnel Doc! And thanks for the tips!


----------



## NTCGRR (Jan 2, 2008)




----------



## jake3404 (Dec 3, 2010)

Black Widows like humid, dark places. A RR tunnel is a perfect place. 

Mickey, I wonder if that pipe has the slits in it. Around here we call that pipe, "drain tile" and it is wrapped in a nylon sock. I would think the slits in the pipe would be great for keeping the tunnel dry as it has a way to drain the water.


----------



## mickey (Jan 28, 2009)

No slits. It's actually culvert pipe that is pretty stout. To get my bend, I estimated and cut the length out of the 20' it comes in. I needed just over 10' then I left it in the sun and started forming it by putting various braces to slowly get the curve I wanted. It was a 3 month or so process I intentionally planned for the hot summer. Since I made the cement collars, I have not gotten ANY water inside and thats with watering the garden above and lots of rain storms. I've been real pleased with it.


----------



## Dan Pierce (Jan 2, 2008)

I used an aluminum 12 inch culvert pipe. Painted the inside ends black. And I was lucky in the position of the tunnel in that the wind blows through it and to date (10 years) no big critters have nested in there, just spiders. 
My next tunnel will be 12 inch PVC that is over 1/2 inch thick that I was given.


----------



## jimtyp (Jan 2, 2008)

Awesome tunnel Marty! Really like the portals tool  

For keeping big critters out I've seen where folks make a portal cover that can be easily attached when not in use. 

For spiders I really like that Home Defense product you can get at most stores. It lasts for a long time too. I would think that a squirt of that initially and then every few months would be enough to keep the small critters out. 

If using something that is solid on all sides (PVC, clay flue, concrete, etc.) that should keep the gophers and other digging critters out (at least the tunnel portion of the layout


----------



## NTCGRR (Jan 2, 2008)

I used to have book ends to cover them till I got to lazy and forgot about them a few times , ran into them. Now I took an old garden hoe and screwed an old broom onto it and it pushes stuff out just fine. 
But then NOW I have TREES. 









Different castings.


----------



## N1CW (Jan 3, 2008)

*At a local garden shop, the owner installed a nice size layout..BUT..*
*complained about having to haul in+out the trains each day. He had*
*build a covered shelf against one retaining wall to cover the 3 tracks*
*but after a year or two, Mother Nature 'had her way' with it.*

*I made a suggestion about using some type of plastic tunnel that*
*I had seen here on MLS+Dan's ....well....several pieces showed up on my*
*next visit......(say some bad words about cutting them here)....*

*All went well with some of the smaller locos and cars but when the*
*LGB big guns came to play.....off when the diesel horns...really!!!!!!*
*We will not talk about the top's of the Mogul Smoke Stack...etc...*

*With the addition of a 1x4 along the length on both sides, enough*
*height was gained to allow those HUMUGUS locos clear the portal.*

*Not the total answer but enough to save lots of round trips to the*
*rolling stock storage shed. When done 'playing trains' just stop *
*them in the tunnel and power down the controllers...tea-time....*

*the_Other_Ray*

Yea....ran out of spray paint...8=)....[/b]

*







*

Here are 3 for the long-long-long train.....on the outer loop[/b]
...dang switch out stopped this from being a 2-for tunnel...8=(....[/b]

*







*


Here is just one for the inner loop short train....[/b]


----------



## skyview (Jun 6, 2013)

Where can you get the 12" plastic ribbed PVC pipe... cant seem to find it? Thanks.


----------



## mickey (Jan 28, 2009)

I had to call around and find a supply place for road building since its mostly used as culverts. It came in a 20 foot section. Ended up driving 40 or so miles as I remember.


----------



## skyview (Jun 6, 2013)

Thanks... only need 4 feet but the PVC approach looks easy.


----------

