由于工作面初次放顶没有完成，顶板巷道、顶板钻孔等不能发挥作用，常发生瓦斯超限现象，必须采取针对性措施。
Because the first caving of work face haven't been finished, the tunnel roof and hole can not be used and gas often goes beyond the limit, so some measures must be taken.
本文介绍了EH4电导率成像系统的原理、特点和该系统初次在煤矿进行的采空区、断层和钻孔位置等物探实例及其效果。
The paper introduced the principle of the EH4 image system and features, also introduced the exploration cases and results in coal mine goaf, fault and bore holes.
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