rational pre-drainage period 合理预抽期
period of drainage 搁田时期
Gas concentrations drop, and the effective gas drainage period of holes is shortened, because pores and cracks in the coal seam become completely developed after gas drainage.
针对煤层钻孔抽放瓦斯后煤层孔隙裂隙发育致使瓦斯浓度下降，钻孔有效抽放期缩短的技术难题，首次提出二次封孔方法。
In design of highway drainage system, the rainfall reappearing period is a very important parameter.
在公路排水系统设计中，降雨重现期是一个非常重要的参数。
During this period, the destruction of the vegetation in Wenyu drainage area leads to the ecology environment depravation of the area.
这一历史时期，文峪河上游植被的破坏，直接导致了流域生态环境恶化。
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