How do I build a tunnel

[railroadboy]

I want my tunnel to be somewhat 2ft underground. But how do i stop it from caving in?

[altterrain]

Look at these threads -

http://www.trains.com/trccs/forums/1026541/ShowPost.aspx

pics of my concrete block tunnels -

http://www.trains.com/trccs/forums/1136609/ShowPost.aspx 

http://www.trains.com/trccs/forums/1145464/ShowPost.aspx

Technique in brief -

I used 4"x8"x16" concrete blocks (the skinny ones) set
tall side up. You would need 3 blocks per 8" section
(sides and roof). I figured where I wanted the tunnels
and dug two trenches about 6 inches wide and about
8-9" deep. I filled them with 2-3 inches of gravel and
set in the blocks and made sure they were plumb and
level. I made up a 80# bag of mortar mix and slapped
in the sides. The extra I used in the middle section
for roadbed. 
The first tunnel was on a straight and is 40" long (5
sections of block) and I made it just 16 inches wide.
I attached the roof blocks with a liquid nails type
adhesive and used a extra hunk of pond liner (but
plastic sheet will do) on top to keep it water and
dirt proof.
The second tunnel comes in from and out to a curve
(10'D) but the inside track is straight. I made its
width about 19". This tunnel is only 32" long (4
sections). Since its shorter I had extra mortar and
used it to set on the roof block and skim coat the
top. I also set rebar in the inset corners of the roof
with mortar to give it a bit more strength.
The blocks come in both solid and hollow versions.
Either will work. I used the hollow ones since that
was all they had at the time. The could also be used
to work a curve at only 8 inches wide and just use
extra mortar to fill in the gaps.

Besides the drain pipe and concrete products, I have seen tunnels made from an open ended box of 2"x12" pressure treated lumber.

-Brian 

[two tone]

A good reply from your first reply. only one comment if you are using track power make sure that water does not get into tunnel water loco moters and electricity do NOT mix loco moters cost also if useing batt power damage can still happen.

[FJ and G]

tunnels are a hassle,

 

keeping them from caving in is the easy part. If you're going 2 ft below, there's drainage considerations.

 

access is a biggie as well; and for some, rodents and reptiles 

[CandCRR]

I used a drain or culvert pipe. So I would not have to worry about water at the bottom I mounted my track on a 2X6 which left a good inch under the board for water to flow through if we got any heavy rains.  The pipe is also at very slight angle.

 If you want a fairly short piece of pipe you may want to check with the Forman at a local construction site to see if he has any leftover pipe.  Sometimes it is cheaper for him/her to give it to you than to dispose of it at a dump.

 

[Anonymous]

  I used chimney flues which comes in different sizes and layed them end to end , but get them big enough  for the track and cars to go through .    Ben

[Dick Friedman]

My only tunnel is made of pressure treated 2 by 12's.  I framed the tunnel lining and roof.  Over it I put a piece of pond liner, as I placed a pond waterfall atop it.  Now my train passes beneath the mountain.  Pix on Flikr under train44buff.

Two things you didn't ask, but are critical.

Make sure there are no joints in the tunnel.  If you've got track power, the joint WILL fail in time and you'll have a dead section.  Don't ask me how I know this.  I use aluminum rail and got two sections (six feet each) welded together to eliminate that problem.  Saved me a pair of clamps, too!  Make sure the track is in guage and alignment, else you'll REALLY need to do the next item.

Also, track or battery, make sure you can reach in to retrieve locos and cars that stop.  They will stop for dirt, critters (or worse, critter poop), derailment.  My rule is all tunnels must be shorter than two times the length of my arm.

[markperr]

I believe two feet underground in our scale qualifies as a subway, no?

Mark

[imrnjr]

My tunnels are a combination of 2x4, 2x6, 2x8 and 3/4 PTL sealed with an asphalt based roofing material, and foils seam patches at the joints of  curve.  I laid out the rail, clamped it together in the shop and matched the cuts to the decreasing radius curve. 

Something to remember if the tunnel has a curve is to maintain enough side clearance for your largest rolling stock a motive units.  I built mine to a minimum of 5.5" from track center line, which will handle anything I plan to put on the road. 

I assembled it less the top, painted inside and out, and sealed the interior with a herculiner truckbed spray.  We then moved them from the shop to the garden, laid in the track, put the top on, sealed and covered them.  These are both 8 to 9 feet long and weigh in at about 125-150 pounds fully assembled (definitely a two man job to place and level). 

I'm just now getting the portals on them, so they have collected some dirt in the interim, which I'll have to clean out.  I can reach past the center from either end with an arm and/or a 36" grab stick (pincher) so clearing any derailments or trouble should be fairly easy. 

 

 

Mark

[piercedan]

I used a 12 inch round aluminum culvert.  I can drive my Gravely tractor over this when constructing, as it can take the weight of a car.  I did back a trailer of dirt over it several times.