C. Vibration strike: it is used in drilling and casing with loosen sand, cobble stone and gravel layer etc.

振动击打：用于松散的砂、卵石、碎石地层的钻进及下套管等。

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C. Vibration strike: it is used in drilling and casing with loosen sand, cobble stone and gravel layer etc.

振动击打：用于松散的砂、卵石、碎石地层的钻进及下套管等。

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