PSI - Issue 84

Mohammad Javad Azari Nezhadian et al. / Procedia Structural Integrity 84 (2026) 1222–1230

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comparison between RC and RC-SFRC tunnel segments under pure bending. This gap in the literature highlights the pertinence of the current study, which seeks to advance further experimental evidence and encourage the development of reliable analytical and numerical design and optimization tools for next-generation precast tunnel linings. 2. Specimen Materials and Geometry The tunnel lining examined in this study consists of a seven-part precast concrete ring, assembled via circumferential joints to form a complete circular segment (see Fig. 1). Each piece labeled I through VII has a defined position within the ring, with Segment I functioning as the key segment. The others (II through VII) interlock sequentially to maintain the continuity and stability required during mechanized tunneling. This type of seven-segment ring system is a standard approach in urban tunneling projects where segment geometry and the order of assembly are influenced by both construction tolerances and the operational requirements of tunnel boring machines (TBMs).

Fig. 1 Schematic representation of the seven-segment precast tunnel lining ring, showing the arrangement of individual segments and the location of the segments selected for experimental investigation.

For the current investigation, only two segments (IV and VII) were selected for full-scale flexural testing. The choice was deliberate: these segments occupy positions in the ring that experience differing bending responses, both during the initial TBM thrust and throughout long-term loading conditions. These specimens also present different rebar configurations while maintaining the same concrete mix design. By subjecting these parts to four-point bending tests under controlled lab conditions, the study aims to capture representative structural behavior from distinct zones of the ring. Details of the shape and material composition of these two segments are provided in the following sections. Table 1 presents a summary of the key parameters obtained from the test performed on the extracted concrete cores, a total of 4 compressive tests and 2 brazilian splitting tensile tests. Table 1. Key parameters from the Compressive tests and the Brazilian splitting tensile tests on extracted concrete cores Key parameters (Compressive Test) Values Key parameters (Brazilian Test) Values Weight (kg) 0.41 Weight (kg) 0.80 Average diameter (cm) 6.07 Average diameter (cm) 6.00 Height to diameter ratio h/D (-) ≈ 1.0 Height to diameter ratio h/D (-) ≈ 2.0 Average failure load (kN) 172.24 Average failure load (kN) 47.73