Steel Fiber and Aggregate Distributions in RC-SFRC Segments for Shield Tunnel Linings: An Experimental and Statistical Modeling Study

This paper focuses on the mesomaterial distributions in concrete segments with conventional rebar and steel fiber hybrid reinforcement (RC-SFRC) for metro shield tunnels, aiming to connect mesomaterial characters with the macrostructural design. Herein, an innovative segment test was designed to provide comprehensive material-phase investigation samples within the RC-SFRC segment space, and comprehensive image processing methods were developed to characterize mesomaterial distributions. Based on the experimental results, material-phase optimal three-parameter probability models were systematically established and evaluated to enhance mesomaterial reconstruction accuracy in RC-SFRC segments. The primary findings are as follows: with increasing core radius, aggregate and steel fiber contents undergo violent, slow, and stable stages. A minimum coring radius r = 50 mm for the coring method is required for reliable mesomaterial identification through image-based methods. Vibrating process–induced mesomaterial settlements and movements produce three statistically significant stratification depths across the segment thickness, corresponding to thicknesses h s = 0 – 70 , 70–280, and 280–350 mm. The three-parameter Weibull distribution substantially improves global material-phase distribution fitting accuracy compared with two-parameter models, as well as beta and gamma distributions, conducive to accurate mesomaterial characteristics reconstruction of RC-SFRC segments.