There have three decisive questions need to solve while drilling in sand gravel layer. The first question is drillingfootage.
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；
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Field tests also show that the self-resonating cavitation nozzle is highly effective in reducing bit wear, increasing drillingfootage and drilling speed.