（解説文要約）
大きな岩を積み上げ、天井と地盤の空間を埋めていきます。

これをボタコヅミといいます。2メーター四方を大きな岩で囲み、中に小さな石を詰め込んで作ります。
完成した後、徐々に天井が重圧で落ちてくると、圧縮され強固なものとなります。

 

 

 

 

 

Botakozumi,walls made of discarded rocks sorted out while mining, were used to strengthen the coal drive. 
They made these walls by first creating the surface of the wall by piling up large rocks in a 2meter square, and next, by strengthening their foundation by adding small rocks into the crevices of these squares.
As the drive ceiling lowered from pressure,the rocks were compressed which strengthened the structure of the wall.