Steel fibers as reinforcement for precast tunnel segments

摘要

Fiber reinforced concrete (FRC) is a composite material with a cementitious matrix and discontinuous reinforcement (the fibers) that may be made of metal, glass, synthetic or natural materials. Among the structural applications of FRC, there is a growing interest in precast tunnel segments to be used with the tunnel boring machine (TBM), where steel fibers may substitute, partially or totally, the conventional reinforcement. In the present paper, the structural behavior of the tunnel segments for the Line 1 of Valencia Metro (Venezuela) are numerically simulated with FE analyses based of nonlinear fracture mechanics (NLFM). The TBM-excavated tunnel has a diameter of about 9 m, a length of about 4 km and is located from about 11 to 21 m below the surface. The tunnel is made of 5 segments with an average length of about 4.6 m and a smaller key segment. In a previous study concerning the new Line 9 of Barcelona Metro, it was demonstrated that the total reinforcement may be reduced by using an optimized combination of conventional and fiber reinforcement. In fact, the conventional rebars could be limited to the chords along the two longer sides (Fig. 1). In the present paper, similar chords combined with steel fiber have been adopted for the Valencia Metro.