Abstract:

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.

Key words: long tunnel, Yanwan tunnel, superlarge karst cave, muck backfilling, bridge crossing, arch protection