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大秦线军都山隧道全长8.4公里,穿越燕山山脉,地质构造复杂,岩层是山火山爆发堆聚体所组成,进口段有670米岩性表层为第四系上更新统洪、冲积松散堆积物黄土质砂粘土和细砂土组成,洞顶覆盖12米左右,隧道跨度12.74米,覆跨比<1,不易形成天然拱,工
The Daqin line military tunnel covers a total length of 8.4 kilometers, crossing the Yanshan Mountains, the geological structure is complex, the rock is volcanic eruptions composed of aggregates, the import section of 670 meters of lithological surface Quaternary Pleistocene flood, alluvial loose accumulation Loess soil clay and fine sand composed of sand, roof covering about 12 meters, the tunnel span of 12.74 meters, span ratio <1, not easy to form a natural arch, workers