CT-Based Quantification of Mesodefects in Soil–Rock Mixtures: Correlations with Freeze–Thaw Shear Strength Deterioration

This paper proposes a quantitative method for evaluating freeze–thaw mesodefects in soil–rock mixtures (SRMs) using computed tomography (CT) image processing. SRM is a typical heterogeneous geotechnical medium composed of soil matrix and rock blocks with varying sizes and mechanical properties. The deterioration of SRM’s macroscopic strength due to freeze–thaw cycles (FTCs) is closely linked to the mesostructural evolution. To investigate this relationship, triaxial and CT tests were performed on SRM samples subjected to different FTCs. The triaxial results showed progressive shear strength reduction with increasing FTCs, while CT images revealed the development of mesoscopic defects. A fuzzy c-means clustering algorithm was applied to segment CT images into four phases: background, rock blocks, soil matrix, and defects. The results indicated that FTCs primarily induced defects within the soil matrix and at the soil–rock interface, while rock blocks remained unaffected under the conditions of this study. A morphology method was further employed to define block boundaries and detect interface defects. By tracking the geometric evolution of defects, the freeze–thaw deterioration mechanism of SRMs was interpreted in terms of defect accumulation and connectivity. Finally, the relationship between shear strength deterioration and defect proportion was captured through a logistic regression predictive formula. This nonlinear formula, characterized by four parameters and an asymptote, demonstrated a strong fit to the test data, with a coefficient of determination (R2) reaching 0.91. The findings provide a basis for linking mesoscale imaging data with macroscopic strength deterioration, offering new insights for freeze–thaw performance evaluation of SRMs.