Assessment of steel-fiber-reinforced segmental lining of Chamshir water conveyance tunnel, Iran: Integrating laboratory experiments, field observations, and numerical analysis

The conventional rebar-reinforced concrete (RRC) segmented lining of the Chamshir water conveyance tunnel (CWCT) in Bushehr Province, Iran, has experienced significant damage issues. This paper presents a comprehensive study involving laboratory experiments, numerical simulations and statistical site-survey analysis aimed at evaluating the mechanical behaviors and structural integrity of steel fiber-reinforced concrete (FRC) and fiber-rebar-reinforced concrete (FRRC) segment types, as compared to the traditional RRC segments. Laboratory compressive, tensile and flexural strength testing provided insights into the impacts of the fiber diameter and content on the ultimate strength capacities of the FRC test specimens. Numerical simulations scrutinized beam and segment models reinforced by the explicit inclusion of traditional rebar and/or randomly orientated and evenly distributed steel fiber reinforcements. The segment simulations were directed at investigating concentrated loading, representative of the jack thrust force applied in installing the segments during the tunnel boring machine (TBM) installation phase. Additionally, a field-monitoring program of the CWCT lining quantified common damage patterns among 545 RRC and 416 FRC segments that had experienced damage during their installation and in-service phases. For FRC beams, increased fiber content correlated with enhanced strength capacity, although the use of larger diameter fibers produced diminishing returns. Compared to the considerable damage expected near the applied TBM jack thrust force for the RRC segments, significantly reduced damage was predicted for both the FRC and FRRC segment types. However, even modest jack force misalignment (of 5–7.5°) led to cracking damage across the segment width for all models, although with the fibers included, the chipping damage was reduced substantially. The findings underscore the potential of FRC and FRRC segment types to achieve better structural integrity compared to traditional RRC segments.