There are great differences among the strengths of roadway roof strata with different lithological characters; and the strata strengths are also different in various coal mines.
新汶矿区巷道顶板不同岩性的岩层强度相差很大，不同矿井的岩层强度也存在明显差别。
There are great differences among the strengths of roadway roof strata with different lithological characters; and the strata strengths are also different in various coal mines.
新汶矿区巷道顶板不同岩性的岩层强度相差很大，不同矿井的岩层强度也存在明显差别。
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