Flexural Response of Precast Tunnel Segments with Hybrid Reinforcement: An Experimental Study

The mechanical performance of precast tunnel lining segments has long been recognized as a basic issue in tunnelling, it arises from the combined effects of soil-structure interaction, concentrated axial forces of the TBM, and bending stresses applied during production, transportation, installation, and service life of these components. The purpose of this experimental investigation was to better understand the flexural behavior of prefabricated tunnel lining components, reinforced with a combination of conventional rebar and steel fibers (RC-SFRC), investigating a four-point bending test. Two segments, taken out from various positions of a seven-member tunnel ring, were selected for the investigation. In the bending test, extensive data recording was carried out using sophisticated instruments covering the monitoring of crack initiation, crack opening, displacement, and force transfer. The experimental data indicated that a linear-elastic phase, along with a post-cracking phase, existed. In the post-cracking phase, stable crack growth, large deformation, and significant tensile force transfer were recorded. Though the data indicated a ductile behavior of the segments, differences existed regarding the peak load, stiffness, and rate of degradation. These integrated results deliver novel and comprehensive evidence on the flexural behavior of precast RC–SFRC segments, with direct implications for improving tunnel lining design provisions.