凤凰山隧道拱顶外露段锚固桩加设套拱暗挖施工技术

凤凰山隧道在距进口210～250 m处与沟壑平交，导致洞身21 m浅埋有17 m拱顶外露，因明挖施工存在诸多困难故采用暗挖。通过方案比选，采用在隧道两侧先施作多根锚固桩，桩顶现筑钢筋混凝土纵梁和套拱，并在拱外回填土后实施暗挖。介绍了施工流程、技术要求以及注意事项，实际施工中取得良好效果。

Tunneling Construction Technology for Addition of Cover Arch on Anchoring Piles in Vault Exposing Section of Fenghuangshan Tunnel

The Fenghuangshan Tunnel crosses ravine at the position 210 ～ 250 m away from the entrance, causing the 21 m shallow tunnel trunk has a 17 m section of vault exposed. Since open excavation has many difficulties, tunneling method was adopted. Through scheme comparison, the method, in which several anchoring piles are exerted at both sides of tunnel at first ; then reinforced concrete longitudinal beam and cover arch are placed on the pile top; at last, tunneling is carried out after backfilling outside arch with soil, was used. In the paper, the construction process, technical requirement and precautions were introduced. In practice construction, good effect was reached.