求翻译：掘进作业产生的粉尘主要集中在x=12、x=13、x=14、x=15所处范围内，并且随着距离作业面的变大浓度逐渐变低，高浓度的粉尘主要分布在巷道的上部，巷道下部粉尘浓度较低是什么意思？

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boring job dust from concentrated mainly in the X = 12, X = 13, X = 14, X = 15 the range, and the distance from the job change the density is low, the high concentration of dust particles are distributed in the gallery, and upper galleries of the dust concentration lower

The tunneling work produces the dust mainly concentrates in x=12, x=13, x=14, x=15 locates in the scope, and along with changes gradually from the work surface fill-out density low, the highly concentrated dust mainly distributes in tunnel upside, lower part the tunnel the dust density is low

正在翻译，请等待...

正在翻译，请等待...