It involves bolting iron plates to the walls of tunnels at regular intervals and placing sledgehammers nearby.
这种方法是通过在坑道壁上有规律的固定一些铁片，然后在在这些铁片附近放上铁锤。
The steep ruggedness of the volcanic terrain made this work very difficult; it required picks, sledgehammers, and a lot of sweat.
由于火山地形险峻陡峭，他们的活干得很艰难，十字镐和重锤都要派上用场，而且汗流浃背。
The steep ruggedness of the volcanic terrain made this work very difficult; it required picks, sledgehammers, and a lot of sweat.
由于火山地形险峻陡峭，他们的活干得很艰难，十字镐和重锤都要派上用场，而且汗流浃背。
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