Excavating a Tunnel Mine

Excavating a tunnel is hard work and time consuming. The rates for excavating by the various races follow. Rates are in cubic feet, per miner, per eight-hour day.

Mining Rates Table

Type of Rock
Very


Race of Miner
Soft
Soft
Hard
Gnoll, Halfling,



Human
75
50
25
Gnome, Kobold
80
60
30
Goblin, Orc
85
65
30
Dwarf, Hobgoblin
90
70
35
Ogre
150
100
50
Hill Giant
250
150
75
Fire Giant, Frost Giant
300
200
100
Stone Giant
500
350
175

A tunnel mine must follow the shifting vein of mineral through the earth. Such a path typically requires a tunnel 10 feet wide and 10 feet high.

When a miner discovers a vein, roll 1d10 and multiply by 10; this is the depth in feet needed to intersect the vein. Mining may now begin in earnest. To determine the path of the vein, roll 1d4 and consult the Mineral Vein Direction Table.

Mineral Vein Direction Table

D4 Roll
Vein Runs
1
North-South
2
East-West
3
Northeast-Southwest
4
Northwest-Southeast

The vein always runs at least 20 feet in the direction indicated. After each 20-foot section is excavated, roll 1d10 and check the Vein Path Alteration Table to determine the new path of the vein.

Vein Path Alteration Table

D10 Roll
Change
1-2
Steep descent
3-4
Shallow descent
5
Curves right (10-60 degrees)
6
Curves left (10-60 degrees)
7
Continues straight/
8
Shallow ascent*
9
Steep ascent*
10
Vein ends

* If the mine starts on the surface, the first time this is rolled it is treated as descent rather than ascent.

Miners who wish to continue working the mine must follow the vein, even if it goes in a direction they do not wish to follow. If the path of the vein takes a course that makes it impossible to follow, such as emerging into thin air through a cliff face, that particular course of the mine has run out. If the vein ends in both directions, the mine is played out. This rule takes priority over the Duration of Mining Site rules.

In unusual circumstances, say a tunnel that ends at a cliff which overlooks a gorge, miners may try to pick up the vein again on the other side. The DM must decide how likely that vein is to continue, depending on the situation.

Shoring a Tunnel

A tunnel mine must be supported, or shored, with wood or stone pillars. Otherwise, sections of the tunnel will almost certainly cave in. Shoring can be done by characters with Mining, Carpentry, or Stonemasonry proficiencies.

Each 10-foot section of tunnel requires two side and one ceiling brace, each at least 1 foot thick. If the tunnel is 10 feet wide and 10 feet high, each brace uses 30 feet of bracing material. Each shoring brace requires four hours to build.

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