Digging a tunnel

[Ch3rnobyl]

Hi Folks,

One of my players wants to dig a tunnel into the enemy stronghold. He has a shovel, and he wants to dig a tunnel with a 3 foot radius (cross-sectional area = 27 square feet) that goes 70 feet down, then 210 feet in a straight direction, and then another 70 feet back up, which will bring them straight into a safe location within the enemy base. (70+210+70)x27 = 9,450 cubic feet of earth that he needs to move.

The rules for the shovel state that it can dig 2 cubic feet per minute, which means that it will take him 80 total hours of digging to complete his tunnel.

My questions to you:
1. Is this a correct reading of the rules?
2. Is there anything extra he needs to do to make a tunnel (e.g. shore it up with beams)? If so, how much time/cost would that take?
3. Is there any special knowledge he needs (e.g. Profession[miner]) in order to complete this project?
4. Is there anything else that needs to be taken into consideration?

Thanks,
Chernobyl

[John Murdock]

if you dig too deep its no longer dirt but rock, the distance before you find bedrock varies from place to place, it can be on the surface or it can be 500 feet deep before you find it, so as a GM i would say to evade shenanigans like that, it will not be too deep before they find the bedrock.

also the deeper you dig the harder it is to dig, since the earth will be very compacted and fill with small rock, which is very hard to remove.

i think a profession miner, and maybe knowledge engineering, is in consideration for doing that project and he will need some form of support so the tunnel do not collapse, and it will need to be big so enough person can dig it up at the same time to speed the operation.

the time taken is to you to decide, same for the money it will cost, but it will never be made in one day, it will take several days, and surely cost a good amount of GP

[Noir le Lotus]

1/ That seems correct.
2/ The longer a tunnel is, the higher the risk of collapsing. Shoring it up with beams is a necessity. The cost can be negligible as you just need some pieces of wood (look how prisoners trying to escape can dig a tunnel with makeshift tools and recycled materials). For the time spent, I think you can easily add 1/3 or 1/2 of the digging time.
3/ as John said, but you can also add Knowledge Dungeoneering (helps to estimate your depth)
4/ Don't forget that digging makes a lot of noise. Enemies have a good chance of hearing it si=o they will try to defend themselves. they could summon an earth elemental to attack the diggers, or damage the tunnel.

[VRMH]

Ch3rnobyl wrote:

Is there anything else that needs to be taken into consideration?

• You can't build a stronghold on dirt, so this building will have a foundation at least as deep as the walls are high.
• He'll need fresh air in his tunnel.
• The exit will start to collapse once the tunnel nears the surface, so he'll need to make that a slope (and have an army ready to rush out).
• Usually mining was done in order to collapse a wall or tower by starting a big fire inside the tunnel, underneath that building's foundation. Not to create a complete passage inside.
• The entrance and the moved earth will need to be hidden, or the enemy will start counter-tunneling.

[Opuk0]

Hah, I'd actually been wondering what the rules are for digging a tunnel, seems like Pathfinder just doesn't want you digging holes, even when you have the burrow ability.

I recall in one of the APs, Council of Thieves I think, there's an enemy towards the end of the first book that had dug out a bunch of tunnels through solid rock. They never say how long it took the enemy to do so.

Edit: Seems I jumped the gun there!

Spoiler:

Dravano has claws on both hands,
giving him two claw attacks each round. These claws afford
him a burrowing speed through soil, sand, and gravel—he can
dig through solid rock at a much reduced rate (about 5 feet per
hour). This replaces the normal tiefling darkness spell-like ability.

[Ch3rnobyl]

Thanks, this is good food for thought. I appreciate the quick responses. :)

[Ch3rnobyl]

Noir le Lotus wrote:

4/ Don't forget that digging makes a lot of noise. Enemies have a good chance of hearing it si=o they will try to defend themselves. they could summon an earth elemental to attack the diggers, or damage the tunnel.

What's the Perception DC to hear your enemies digging a tunnel up underneath your stronghold?

I'm running "Against the Giants," modified for Pathfinder rules. They're trying to figure out a sneaky way to get in & out of the Steading
whenever they want. There is quite a bit of rock below the Steading, so...

As an aside: The only player who is against the plan is the one & only spellcaster, who keeps reminding the others that she can cast teleport to get them in and out. But the ninja wants to dig a tunnel and has convinced the others that it's a great idea. They're debating it as I write this post.

[Opuk0]

Ch3rnobyl wrote:

Noir le Lotus wrote:

4/ Don't forget that digging makes a lot of noise. Enemies have a good chance of hearing it si=o they will try to defend themselves. they could summon an earth elemental to attack the diggers, or damage the tunnel.

What's the Perception DC to hear your enemies digging a tunnel up underneath your stronghold?

I'm running "Against the Giants," modified for Pathfinder rules. They're trying to figure out a sneaky way to get in & out of the Steading
whenever they want. There is quite a bit of rock below the Steading, so...

As an aside: The only player who is against the plan is the one & only spellcaster, who keeps reminding the others that she can cast teleport to get them in and out. But the ninja wants to dig a tunnel and has convinced the others that it's a great idea. They're debating it as I write this post.

Why are they trying to get into the Steading in the first place? Are they trying to kill the giant leader or something like that?

Keep in mind that while digging the tunnel will take 80 hours total, you'd still need to take breaks of 8 hours for rest.

There's also the matter of hiding all the displaced earth. Not to mention that if it's only 210 feet distance, and into the middle of the steading, the dig site is gonna be incredibly close to the steading. Like, within sight of anyone patrolling the area.

Try stressing that there are patrols around the Steading, or other time factors that might make digging a tunnel not the best solution here.

[kadance]

It is my assumption that digging with a shovel at a rate of 2 cubic feet per minute assumes you are able to stand upright, have plenty of room around you to swing a shovel, and have room to dump 2 cubic feet of dirt somewhere other than the hole you just dug.

Check out this XKCD 'What if' for some pertinent information: LINK

Granted, the speed the question proposes is way faster, but a lot of the effects, such as needing 150 horsepower to lift rubble up a 60' vertical hole, etc. are applicable.

Additionally, this SITE is absolute gold for tunneling information.

UMICH.EDU Tunneling Article wrote:

By the 6th century B.C., it has been estimated that the advance rate of a hand-worked tunnel in hard rock was perhaps 9 meters per year. (Beall, 1973) Today, nearly three thousand years later, the advance rate in a given excavation is increased over that by two or three orders of magnitude. (Mahtab and Grasso, 1992) The advent of explosives, first black powder, then nitroglycerine and dynamite, issued in a new age of excavation.

So, in the early iron age the given rate for tunneling was about 30 ft per year.

My advice to your player:
Create Water
Transmute Mud to Rock
Stone Shape.