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

Abstract 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>r</mml:mi> <mml:mo>=</mml:mo> <mml:mn>50</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mm</mml:mi> </mml:mrow> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mi>–</mml:mi> <mml:mn>70</mml:mn> </mml:mrow> </mml:math> , 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.