Leak of pulp, low efficiency and fall down of hole wall are the common problems when we drill in thick loose sand-pebble layer.
松厚的砂卵石地层中钻进时，除钻效低外，冲洗液的漏失和孔壁不稳定是钻进中所面临的最大障碍。
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The cushion layer for the dam is constructed with the material prepared mainly with natural sandy gravel and mixed with proper amount of pebble and coarse sand.
大坝垫层料采用以天然砂砾料为主、掺入小石和粗砂以调整级配的方式生产。
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