I have always made my tunnels with access through the sides or from the top through a lift out/off sections. Not only does one need to get to derailed equipment but for maintenance.
I've never had a problem blending layers of foam. I stack and glue the foam, then shape it with either a knife or a hot wire foam cutter. Next I cover it with a layer of sculpt-a-mold then scenery assorted stuff.
Much of my layout is a subway tunnel, which is on the first base layer of foam. The tracks above it sit on a second layer, and between the two I generally have scraps of 1x2 (laid flat) to boost the separation. Here's a shot of one end of the layout:
After replacing the liftoff sections, it looks more like a standard train layout:
There are 5 liftoffs in this picture, and 2 others elsewhere on the layout. Each liftoff is small, and most are made of foam. (2 are 1/4-inch foamboard, and one is masonite. I was experimenting.)
The foam is easy to work with. I coat it with Gypsolite, and bridge gaps with plaster cloth. Besides that, I had a lot of small foam chunks to work with, so it was just a handy material for terraforming.
(Click on the pictures for a larger view.)
It takes an iron man to play with a toy iron horse.
Actually, RT, I'm with you. I make my tunnels out of foamcore painted black on the inside, with balled newspaper and hardshell over the top. The tunnel is in the corner and against the backdrop, so it doesn't have a back. Disconnect the backdrop panel, reach in, grab derailed equipment, rerail or remove.
If your tunnel's in the middle of the layout, simply attach one wall of the tunnel with masking tape instead of glue, and make the scenery on top removable.
Easy-peasy.
Connecticut Valley Railroad A Branch of the New York, New Haven, and Hartford
"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford
Mr. Poteet,
I will side with you regarding your dislike for stacking foam. I don't like that method because no matter how hard the users try, the horizontal seams in the layers of foam are visible and therefore distracting to the overall appearance of the scenery.
I used the cardboard strip method to create the underlying structure for my scenery; once formed it was covered in plaster cloth to form the hardshell. I can reach to the top of the 'mountain' from the inside of the tunnel if needed.
Don Z.
Research; it's not just for geeks.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
From the far, far reaches of the wild, wild west I am: rtpoteet