岩湾隧道特大型溶洞处治技术

湖北恩利段高速公路岩湾隧道ZK250+135~+166段有特大型溶洞发育,隧道穿越溶洞中部,周边存在大范围的空腔,采用普通结构隧道无法跨越。为了保证施工安全、运营安全及工程进度,采用洞渣回填、桥跨和拱形防护等处治措施,即:洞渣回填至仰拱顶作为施工通道及拱形防护的基础;桥梁作为行车道部分,上部结构采用2×16 m的连续组合梁桥,下部构造桥墩采取桩基接帽梁、扩大基础桥台;拱形防护(钢筋混凝土套拱+混凝土护拱和沙袋缓冲层)座落在回填的洞渣上,防止可能发生的洞顶坍塌对隧道防护造成结构性破坏。施工和运营初期的实践证明,该溶洞处治技术措施可靠、合理,可以确保隧道施工安全及运营安全。

Case Study on Coping with Super-large Karst Cave in Construction of Yanwan Tunnel

There is a super large karst cave in the section of ZK250+135～+166 of Yanwan tunnel on Enshi Lichuan highway. The tunnel crosses the karst cave along the center and there is large clearance around the tunnel structure. Therefore, the tunnel cannot cross the karst cave by conventional means. The following innovative measures are taken to facilitate the tunnel to cross the karst cave, so as to guarantee the construction safety, operation safety and project schedule: 1) Mucks are backfilled in the karst cave to reach the elevation of the top of the invert and are used as the construction access road and the foundation of the arch shaped protection structures; 2) A bridge is built and used as vehicle passing structure; the super structure of the bridge is of 2×16 m continuous composite girder, the piers of the bridge are of pile foundations and cap beams, and the abutments of the bridge are of enlarged foundation; 3) Arch shaped protection structure, which consists of reinforced concrete protection arch, concrete protection arch and sand bag buffers, is located on the mucks backfilled, so as to prevent the protection structure from being damaged by the falling rocks. The engineering practice shows that the measures taken are reliable and rational and can guarantee the safety during the construction and operation of the tunnel.