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[Juxtap0se]

why am I having so many cave ins? I'm trying to remove hilltops in a minor terraforming project and I've had about 9000 cave ins. the last one chucked a legendary miner into a lava moat.
My method is to have all trees removed and channelling down one z level at a time from the top of the hill. There is nothing above my miners as the dig and they are not channelling into anything except dirt. What gives?

[Juxtap0se]

well i took a closer look in the wiki. Could the problem be that my miners are working too close together?

[AutomataKittay]

Sounds like your miners were trying to tear up where there're dug out level under there or over the moat. Tiles not connected N/E/S/W or from above or below ( by wall or support in same tile in same Z or under it ) will cave in.

I've not had a cave-in from channeling solid ground, yet, a lot of miners falling while they channels under them, though.

Nothing of above sounds like your case, though, so I'm not sure what's happening.

[smjjames]

My method is to have all trees removed and channelling down one z level at a time from the top of the hill.

that is probably the problem right there, dwarves will try to channel a square someone is standing on and don't pay attention to whether something might cave in or not. A safer (and probably more efficient) technique is to designate the whole layer as ramps, that way the stone layer AND the floor above it get mined out.

As for why exactly, you'll have to observe what they are doing. You might get some collapses from saplings growing into trees.

[Larix]

Miners channelling away the floor under each other's feet only causes dropping miners, not cave-ins.

Check if the z-level above your miners _really_ is empty, it's easy to miss a spur of rock or two.
A more likely cause is if part of the level below is already mined-out. Mined-out areas don't support anything on the level above, so if the area above is channelled away in the typical erratic pattern, you'll end up with disconnected floor tiles that spontaneously realise they have no support any longer and come crashing down.

[Juxtap0se]

yeah like I said I'm starting from the very top down. I had just tried the up-ramp suggestion. had another cave in. The two miners were right next to each other and my guess is that one dug out the ramp under the other one which seems to cause the cave in. I guess only one miner at a time should be doing this terraforming  that'll take forever

edit: the ramps seem to take longer than channelling. Mostly because the ramps don't happen in a nice orderly pattern; digging is much more random so the miners are running all over

[smjjames]

Are you trying to channel multiple levels at once? That'll definetly cause cave ins since the dwarves do it inconsistently.

Do freestanding ramps cause cave ins? I don't think they do and I've designated large areas for up ramps without problems of cave ins.

Are you ABSOLUTELY sure there are no trees? Because they will grow after you cut them down and it's entirely possible for a tree to grow just before the miner finished the ramp, but that wouldn't be often.

[AutomataKittay]

yeah like I said I'm starting from the very top down. I had just tried the up-ramp suggestion. had another cave in. The two miners were right next to each other and my guess is that one dug out the ramp under the other one which seems to cause the cave in. I guess only one miner at a time should be doing this terraforming  that'll take forever

edit: the ramps seem to take longer than channelling. Mostly because the ramps don't happen in a nice orderly pattern; digging is much more random so the miners are running all over

Under? Are you trying to strip multiple Z's at once? Cuz that will definitely smash someone even with single miner. Otherwise, I don't know, but if you want to be sure, pave dirt roads to destroy any tree sprouts.

Your situtation seems to be a bit... unusual if it's not multi-Z stripping at once.

[smjjames]

nvm

[Juxtap0se]

Are you trying to channel multiple levels at once? That'll definetly cause cave ins since the dwarves do it inconsistently.

Do freestanding ramps cause cave ins? I don't think they do and I've designated large areas for up ramps without problems of cave ins.

Are you ABSOLUTELY sure there are no trees? Because they will grow after you cut them down and it's entirely possible for a tree to grow just before the miner finished the ramp, but that wouldn't be often.

there are no full trees, perhaps sprouts, but no full trees. I am certain that I am only removing one z level at a time. This has happened several times across different embarks. I really think that the miners are digging the ground out from under each other. I've noticed it only happens when the miners are right next to each other. stupid dorfs!

from the wiki: "Miners also don't check that there's nobody standing on the floor that will shortly cease to exist - meaning that several miners channelling floors in the same area are a danger to each other. So you should allow only one dwarf to mine out floors in an area at a time. " This might also happen with upramps? The wiki continues with saying that upramps should be used instead but doesn't specifically say whether or not digging at another's feet could trigger cave-ins...

mostly unrelated: how do you tell if a siege is over?

etiquette question: if I have multiple questions, should I start another thread? (much like the last tag-on in this post)

[smjjames]

What about those random free standing up ramps that get left over? Not sure if they can trigger caveins.

Maybe if you upload the save or take a screenshot of what is going on? Not sure if there is a bug where seedlings somehow get stuck in the air and when they grow, they cause a cavein, but that would show as a cavein where your miners aren't.

[FuzzyZergling]

Dwarves digging out the ground from beneath each other's feet shouldn't cause cave-ins. Cave-ins only happen when a tile is unsupported, and if you do it one level at a time the tiles should always be supported by the ground under them.
Do you think we could get screenshots?

[Juxtap0se]

Dwarves digging out the ground from beneath each other's feet shouldn't cause cave-ins. Cave-ins only happen when a tile is unsupported, and if you do it one level at a time the tiles should always be supported by the ground under them.
Do you think we could get screenshots?

FuzzyZerg I wish I could. Shortly after posting there was a goblin ambush. Thought I got them all so I sent out the rats to collect the goblinite but I guess I had missed a squad of goblin archers who proceeded to decimate my dwarves. Bad time for a ragequit, I guess.
I will, however, keep this in mind for my next fort and will try to post screenshots if possible. I would video it up but I don't know how/don't have the software. I will post back here if it occurs again (which is likely; like I said, it has happened many times across multiple embarks).