在砂卵石地层中勘察钻探时，要解决三个关键性的问题：一是钻进进尺问题；
There have three decisive questions need to solve while drilling in sand gravel layer. The first question is drilling footage.
在砂卵石地层中勘察钻探时，要解决三个关键性的问题：一是钻进进尺问题；
There have three decisive questions need to solve while drilling in sand gravel layer. The first question is drilling footage.
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