I've been meaning for quite a while to do a little guide to piercing aquifers. I finally got around to it.
InvestigationWhen you hit an aquifer the first thing to do is find out how deep it is, so dig an up/down stairs into it, this will reveal the tile below the aquifer layer. If it is bedrock or clay, you know it's only 1z deep. If however it's another aquifer layer then it's indefinite layers deep so use
Quantum Mechanic's twin-slit method, the second one which is in the spoiler tags (although I use a faster, simpler, optimized variant, which results in a 1x2 staircase down one of the slits).
Using a cave-in to pierce a 1-z aquifer.Conceptually, the cave-in method involves removing a section of aquifer-bearing sand, leaving a pond sitting on the underlying rock. Next, a dirt plug is dropped into the pond, displacing the water. You now have dry dirt sitting on dry rock and can dig a staircase through.
The method I'm going to show here is a very quick and easy cave-in based technique which will get you through the most common type of aquifer; 1z deep with 2 dry layers of soil on top. This technique requires no supports/levers, a little bit of digging and just 1 wood or stone. It is safe, reliable, and only takes a couple of minutes.
Channel around a 4x4 block of soil.
Now, the next level down, channel out a single tile next to one of the corners. Build a constructed wall in that space, this will prevent the plug from collapsing until we want it to. Channel out the rest of the tiles.
Below the plug, mine and channel out a 4x4 "pond" (you should channel ponds as a sliding door opens, from the inside out). Also dig out some additional channels so the displaced water can flow back into the aquifer.
Now release the plug by deconstructing the wall from a specially dug passage. The clever bit is that a dwarf can deconstruct through a diagonal, but cave-in dust can't travel through a diagonal (it wont work if the wall and access passage aren't in a corner). This keeps the dwarf triggering the cave-in completely safe, without having to mess around with a support and lever.
CRACK-A-BOOM!A section of the cavern has collapsed!Wait a few moments for the dust to clear and water to drain away. Now dig through the core of the plug to the rock below.
A few more tips:
- Constructed walls deconstruct in a cave-in, so can't be used as part of the plug. But they can be used to protect the dwarf doing the deconstructing. Doors and hatches also stop cave-in dust.
- Don't dig the plug out too close to the wagon or surface workshops, dwarves WILL get sucked in. 4 or 5 tiles seems safe. Avoid having non-diagonal connections to underground spaces.
- Don't have the access staircase too close to the plug, since the dwarf who deconstructs the wall might rush down to ground zero, or to the surface, and get knocked around by the cave-in dust.
- Consider using a door to block access to ground zero, since idle dwarves sometimes go to the lowest point to hang out. Otherwise, keep everyone occupied.
- It is possible to use this method for stage1 of penetrating a multiple layer aquifer, but you'll probably want to make it a 4x6 plug for a 2x4 dry area. This saves time and a bunch of wood for sealing the walls.
If people like this walk through, I might do a couple of other methods.