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[vanatteveldt]

I am trying to channel out a 13-z level deep 3-tile wide moat. I thought that if I would give the channel orders level by level there should be no risk of a cave in, as any tile is always supported by the ground below. However, I am getting lots of (harmless) cave ins. I then figured I'd give the orders row by row for each level, ie do it in three channels, each 1 tile wide. However, I still get cave-ins.

Why do I get cave-ins even if there is solid floor below the level I am working on?
Would it help to first mine out the whole moat, and then channel the floors one row/level at a time? [edit: no, doesn't seem to help. I really don't understand what is collapsing here...]

Edit: it seems that digging a ramp and then removing it (e.g. d-r + d-z) allows for safe channeling. I still don't understand what is caving in, though... Or is the problem that I am working with two miners?

Screenshot:


This is at the edge of the map, but I don't think that matters?

[Starver]

I don't exactly understand how you're getting your problems[1], but the method I use is to (per Z-level!) designate it all to be ramps, and then let them take care of that before moving onto the next layer.  Note: Do not ramp the soil beneath a tree, or other isolated "full, otherwise unsupported" blocks, and for that reason I might make the top impression by channelling the empty ground to spot any problems like that, then move down two levels to set up ramps, safely, on the level below the floor I just created.

Then, when done (or the very last ramp-designations are seen to be in progress/at the head of the queue, if I'm worried about other miners being idle for a short time), designate the ramps on the layer below.  You do not need to de-ramp whatever ramps remain on the level you've just ramped.  They do not cave in (not "left over from ramp-digging" ones, anyway... constructed ones could, of course, if left unsupported by the excavation's side).


[1] Although a dwarf chanelling an 'island' block, left after all around has been chanelled[2], may well be falling off his or her perch on completing that.

[2] Or in the case of a well, currently surrounded by wall and thus having nowhere else to stand.

[vanatteveldt]

Thanks, jump using "carve ramp" works like a charm. I was removing all the ramps before going to the next level since I thought that these might be causing the cave-ins, but I guess not.

(maybe a channel on a tile with a ramp on it will cave-in the ramp, while a carve ramp will not? Still strange, though...)

[Starver]

I'm somewhat sure that channelling a tile with a ramp (left over from carve ramp on that level or channel on level above, either way, because it's functionally the same SFAIK) shouldn't have problems.  However, if what you're now doing is working then you're now unstuck.  And (as you get time) you can finesse the method and see if (and why) it 'breaks' again.

IME, I can only imagine you getting cave-ins if you're (while looking at the 2D slices) forgetting about a 'floating' rock that's left on a higher level.  Thinking 3D is something (like with "The Matrix") you eventually get a hang of, but even so someone who "doesn't see the code any more" can still end up fooling themselves on some aspect of construction or other.  I know this to be true, for reasons unrelated to your actual problem, but still analogously similar.

Maybe "Stonesensing" the level (before and after an 'incident') might give a view of the situation that clues you in?  Not sure, I've not used it myself, only seen others' screenshots of its use.

[vanatteveldt]

I'm pretty sure that there was nothing (except for leftover ramps) left on z+1. The first cave-in, maybe, but after that I thoroughly checked.

The strange thing is, I've often asked a dwarf to channel right done in a 1x1 hole, e.g. for a well or garbage chute, and never gotten cave ins.

Firing up a new world to see whether I can recreate and understand the problem....

Edit: I give up... I can't reproduce the cave ins. When I get back to my proper fortress I will see if going back to channelling rather than ramp-carving will trigger it again, but in the meantime I just don't understand... but it's probably a stupid user error...

[Starver]

Not that I think a channel would do anything like this, anyway (I stand to be wrong[1]!), but in a 1x1 well/chute-digging exercise then I'd expect everything to be supported from all four sides for whatever instant there might (hypothetically) be that the Z-1 has been dug out (or changed to ramp) while the Z=0 of the old floor (or ramp) still exists.  Thus no cave-ins.  You'd get the dwarf dropping 1Z (and possibly dropping boulders on him or herself, prior to this being fixed), but no dust.

However, you're happy.  And if you're happy then that'll be $39.99 support charge, please, payable within the next 14 working days I'm happy.


[1] But except where I accidentally dig through pre-existing voids (of my own making, or natural), it's generally safe to do so in the way I've normally done it.