I've been thinking about megaproject design and scaffolding recently, since I want to carve the side of a mountain, already pretty steep, into a sheer cliff and then turn it into Mt. Dwarfmore. Searching the forums for "scaffolding," I keep coming across people saying things like "Be sure to start removing your scaffolding early, because it takes FOREVER." I think I've found a way to make easy-to-remove scaffolding. I've only been playing DF for a few weeks, though, so I'd like someone to check this idea and see if it works.
The key idea is to build your massive up/down staircase a few tiles AWAY from your project. That gap will be filled in by bridges, since they do not provide support. (We're trying at all costs to AVOID having the scaffolding be supported by the project.) Oh, and make sure your staircase has more than one stair in it, because what you're going to do when you're ready to tear it down is this:
Side view, BEFORE
XXX ?F: Top story of your scaffolding
(...) *F: As many floors of scaffolding as your project needs
XXX 2F: Second story of your scaffolding
_XXX_ 1F: Ground level, where you built your scaffolding
..... B1: First layer UNDER your scaffolding
Side view, AFTER
XXX ?F: Top story of your scaffolding, unchanged
(...) *F: More floors of your scaffolding, unchanged
XXX 2F: Second story of your scaffolding, unchanged
__I__ 1F: Ground level. One stairs was removed and replaced by a support, then the rest were removed.
.OOO. B1: First layer UNDER your scaffolding. Walls were built everywhere directly under a piece of scaffolding that's going to fall.
X = Up/down stairs (or just up stairs on the ground level)
(...) = As many layers of stairs/scaffolding as you want.
_ = Floor
. = Empty space
O = Wall
I = Support
Once you've built walls to catch the falling scaffolding (don't want it to punch through floors and down through your fort, after all), dig out ONE square of the bottom staircase and replace it with a support. Then dig out the rest of the stairs, hook the support up to a lever, gather your dwarves in a safe spot, and
pull the lever.
I've tested this on a small scale, and it works. What I don't know, and what I'm hoping some more experienced DF players can tell me since I don't currently have the skill to get a fort past year 4-5 (I keep dying to goblin invasions), is whether it will work on a larger scale. Specifically, will the bridge material come down in unexpected places when the stairs they're attached to deconstruct? Will the walls in layer B1 need to be a lot larger to cover the areas the bridges extended to? Will any rocks and/or logs travel horizontally after you pull the lever, or will they all fall straight down?
If this works, though, then scaffolding teardown will be a snap: all you have to do is build one layer of walls, and tear down one layer of stairs. Or better yet, just don't use the first layer under ground level at all when you're first digging out your map (your first staircase goes two levels down) and then you've got a pre-constructed safe landing zone for scaffolding material, with no extra effort required.