E.8.2 Add Wooden Shoring [1790]

Time to learn: 21 days.
Time to use: 7 days.
Requires: ten workers [11] (not consumed)
Requires: 25 wood [77]

Use of this skill adds wooden shoring to a mine shaft. Normally the chance each month of a cave-in in a mine shaft is (depth/300)%. Wooden shoring reduces this chance by 2.3%.