浅埋土岩复合段隧道冒顶分析与防治

通过对正习高速公路隧道浅埋段开挖过程中坍塌冒顶事件进行分析，提出冒顶处治措施，并建立隧道风化残积深度处于拱顶以及拱顶以下1 m的数值模型，进行无超前支护不同开挖步距的变形特征数值试验，试验表明无超前支护情况下即使采用上下台阶法对隧道进行开挖0.6 m,拱顶的围岩变形最大仍达到3.578、4.789 mm,隧道拱顶残积体对隧道开挖后续支护作业产生较大安全风险。在风化残积深度处于拱顶以下1 m时，原设计小导管纵向间距由2.4 m调整为0.6 m后，开挖0.6 m的拱顶最大变形由2.348 mm降低至1.747 mm,结合现场坍塌冒顶事件，为确保后续隧道浅埋土岩复合段落施工安全，提出了冒顶防治措施并在隧道开挖施工中取得良好的效果。

Analysis And Prevention of Tunnel Roof Fall in Shallow Soil And Rock Composite Section

Based on the analysis of collapse and roof fall during the excavation of a shallow buried section of an expressway tunnel, the treatment measures for preventing roof fall were proposed, and a numerical model was established with the tunnel weathering residual depth at or 1 m below the arch crown. The test of deformation characteristic values of different excavation steps without advance support was carried out. The test shows that the tunnel face excavated 0.6 m by upper and lower bench excavation method without advance support, the maximum deformation of surrounding rock of the arch crown still reaches 3.578 mm 4.789 mm, the residual mass of the tunnel arch crown has a greater safety risk to the subsequent support operation after tunnel face excavating. When the weathered depth was 1 m below the arch crown, the longitudinal spacing of small conduits in the original design was adjusted from 2.4 m to 0.6 m, the maximum deformation was reduced from 2.348 mm to 1.747 mm mm of the tunnel arch crown by tunnel face excavating 0.6 m by upper and lower bench excavation method . In combination with the collapse and roof fall event, in order to ensure the construction safety of the subsequent shallow buried soil rock composite section of the tunnel, roof fall prevention measures were proposed and good results was achieved in the tunnel excavation.