hard roof meaning in English

坚固顶板
坚硬顶板

Study on hard roof working face first pressure managing way
坚硬顶板工作面初压管理的研究
Ground pressure behavior of hard roof mining face
复合型坚硬顶板高档普采长壁工作面开采实践
Controlling design of working face with thick and hard roof
高档普采工作面端面顶板的有效支护
Safe mining technique for coal face with large mining height and hard roof
坚硬顶板工作面矿山压力显现特征
Roof shortening technology of plow faec under the condition of two hard roofs
条件下刨煤机工作面顶板弱化技术

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