The case of accidents, the proposed blasting mining roof caving face the basic requirements for control and prevention of incidents of roof effective measures, must learn.
该文通过事故案例分析，提出了炮采放顶煤工作面顶板控制的基本要求和预防顶板事故发生的有效措施，有一定借鉴意义。
The smelter, owned by Met-Mex Peñoles, part of a big Mexican mining group, ran without a roof from 1901 until 2000, blanketing the surrounding area with layers of fine black powder.
这家冶炼厂归Met-Mex Peñoles所有，它是一个大的墨西哥矿业集团的一部分，1901年建厂时它连厂房屋顶都没有，到2000年该厂把周围的地区盖上了一层层细的黑色粉末。
The increase in mining height makes the weighting of immediate roof become more violently, which requires that the support strength should increase accordingly.
由于采高加大使基本顶来压更加强烈，支架的支护强度更要加大。
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