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。
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.
通过该井大井眼巨厚砾石层的钻进，对钻井工具的制造也提出了新的要求。
Through the drilling of thicker conglomerate in large borehole, the new requirement for the manufacture of drilling tools has been put forward.
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