Decided to do another test, using Merendel's method but with a larger cave-in. Embarked on a similar map, but only a pick, a proficient (5) miner, and 6 peasants this time.
The cart was caved-in down, and last ramp to surface (for the cave-in triggerer to get down, wasn't necesary this time, as the cave-in knocked the peasant selected down into the gopher hole) was removed the next day. Stupidly, the peasant that triggered the cave-in ran up to clean herself in a pond meanwhile, but even with waiting for her (one of only 2 females) to return, and some messing around with the "oh, I'm going to stand on the spot where I'm trying to construct a wall" bug, the dwarves and the yaks were walled in underground on the 8th of Granite. So 5th-6th is definitely doable.
Then I started digging a 11x11 area and a 13x13 square of upstairs on Z+0, so 2 steps larger than Merendel's original (reference is
this post). I dug out Z+0 and Z+1 mostly identically to Merendel, but decided not to dig out the central up/down staircase on Z+1 (and if you don't dig that, you don't really need the central staircase on Z+0 to be up/down either, just down would be fine, but I kept it since I'd already dug it out).
, and to already remove every second up staircase on Z+1 (for a bit less surface exposure later)Don't do this, dwarves can't channel up diagonally like I thought they could.. The miner and a peasant decided to take a drink of aquifer water on 22nd Granite. Z+0 and Z+1 were dug out on the 25th of Granite, the miner (very strong, agile and tough, this time) had reached 9 skill by now:
You should have a ring of up/down stairs, not alternating up/down and down, on Z+1. I channel out 3 rings, one at a time, outside->inside, of the splash area already at this point, for useful training, just leaving a 5x5 in the center to do the chicken run + access to the 5x5.
Also removed all the upstairs except the one just in front of the access tunnelDon't do this YET, either, or you'll have a more finicky time channeling out the stairs on Z+1 later. It's the 3rd of Slate, the miner skilled up to 10 from that: no training, just the initial 5x5 gopherhole, 10-tile tunnel from gopher hole to 11x11 meeting area, ~12-tile tunnels on 2 floors to the work areas above.
You should have a ring of up-stairs, not floor, on Z+0. Did a succesful test chicken run elsewhere. Was worried about peasants or the miner wandering in for water just when I want to do the cave-in, so dug them a little water channel in the meeting area. Did the chicken run down in the centre of the work area. Saved for potential save-scumming, just in case I was wrong about the central staircase tile on Z+1. Which was useful, as I immediately failed at single-stepping for the chicken run. After successfully single-stepping, the chicken run was a success. Then channeled around the chicken run on Z-1 exactly like Merendel, and channeled out the remainder of the splash-down area on Z+0. Z+0 to Z-2 are now ready for the cave-in:
You should have a ring of up-stairs, not floor, on Z+0. Next I just channeled away the ring of floor on the surface from Z+1, then channeled all but the trigger-stair away from Z+1. I hadn't checked earlier for trees and had to dfhack a saguaro out of existence (since I had no axe... and actually changed it to a dead sapling, because I figured out how to do that before I figured out how to magic it away). Did have a bit of trouble (the red text above), but got it done in the end. With all those issues, it was the 13th of Slate before I was ready to trigger the cave-in. As it turns out (did one run, savescummed, repeated), I'd recommend removing the central up stair on Z+0, or it will support the central cave-in tile. You can of course just mine it out later. No screenshots of this, should be pretty obvious. After the cave-in:
Note that there should, again, be a ring of up stairs on Z+0. On Z-1, that's as much as I can dig out, if I dug out a bit more, I'd open up to the aquifer again.
This was 2 steps larger (maintining a single-tile shaft) than Merendel's, he had a 5x5 center area for the water to spread out to, this is 9x9. This level would end up with only 1/7 water (9*7 units of water spread over 81 tiles), if I had waited for the water to evaporate fully on Z+0 after the splash, instead of just channeling the spread-out area immediately. I still had to bucket out the central staircase tile at Z-2 before I could get to the tetrahedrite beneath. And had to channel out the stairs on Z-1, so 1 wood gets temporarily tied down to that too.
So yea, the no-wood method is better, since this still required 1 bucket + 1 wood for stairs, and at least for me, took longer. With good design (meeting area close to bucketing area) and the minimal footprint Merendel had, it's probably competitive with the no-wood pierce in terms of time, but exposes you to the surface while you do the final prep for the cave-in, trigger it, and empty the water with buckets.