Steel Fiber Reinforced Concrete Segments for Shield Tunnels: A Comprehensive Review of Mechanical Performance, Design Methods and Future Directions

Steel fiber reinforced concrete (SFRC) has become a feasible alternative material for traditional reinforced concrete (RC) segments in shield tunnel engineering due to its excellent crack resistance, toughness, and durability. However, its design parameters have not yet been standardized, and research at the material and structural scales remains relatively fragmented, lacking a unified design framework, which limits the widespread application of SFRC segments. This paper provides a comprehensive review of the mechanical performance and design methods of SFRC segments, focusing on four aspects: (1) research methods for mechanical performance, including experimental analysis, numerical simulation, and artificial intelligence algorithms; (2) theoretical calculation methods for flexural and shear bearing capacity and crack width; (3) mechanical response characteristics, including deformation modes and crack propagation patterns; (4) key influencing factors, such as matrix strength, steel fiber types, dosages, and aspect ratios. The study systematically reviews relevant research methods on the mechanical performance of SFRC segments, evaluates the applicability and limitations of existing theoretical calculation methods, and ranks the factors affecting the mechanical performance of SFRC segments from the perspective of material composition. Finally, based on the review, future research directions for SFRC segments are proposed, providing a systematic reference for the development of design standards, improvement of mechanical performance, and full-lifecycle reliability assurance of SFRC segments.