最常见的空间是那些由松散的、未固结的砂和砾石组成的颗粒（沙粒和小卵石）之间的空间。
The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel.
振动击打：用于松散的砂、卵石、碎石地层的钻进及下套管等。
C. Vibration strike: it is used in drilling and casing with loosen sand, cobble stone and gravel layer etc.
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