sand-gravel layer 砂砾石层
sand gravel layer 砂卵石地层
sand and gravel layer 砂卵石垫层
sand layer with gravel 含卵砾石砂层
thick sand and gravel layer 深厚砂砾石层
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。
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。
But for triple stratum foundation, if the top sand layer is relatively thin, piping is vertical. The damage zones are large in width and depth that expand to the sand layer and gravel layer.
当三层堤基浅砂层较薄时，将发生深层管涌破坏，管涌破坏区涉及浅砂层及下部砂砾石层，其宽度和深度较双层堤基大，出口涌砂量也较多。
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