Mineralogical controls on the geotechnical behavior of clayey soils in the Greater Tunis region (Tunisia): A multivariate statistical approach

Abstract

• Mineralogical analysis of the geotechnical behavior of clay soils in Tunis. • Clay minerals increase plasticity, while quartz reduces it. • Carbonates increase shear strength and soil rigidity. • Organic matter increases compressibility and decreases strength. • PCA reveals coupled mineralogical and mechanical interactions. Understanding the influence of mineralogical composition on the geotechnical behavior of clay soils is essential for improving soil characterization and the design of civil engineering structures in rapidly urbanizing regions such as Greater Tunis (northern Tunisia). This study examines the relationships between mineralogical composition and the geotechnical properties of clay-rich soils. A total of 65 samples taken from 22 boreholes distributed across eleven sites were analyzed by X-ray diffraction (XRD) and geotechnical tests, including the plasticity index (PI), undrained cohesion (Cuu), friction angle (ɸuu), compression index (Cc), coefficient of consolidation (Cv), and Ménard limit pressure (PL*). Statistical analyses confirmed the reliability of the data. The results reveal strong correlations and other moderate but consistent correlations, indicating that soil behavior is controlled by the combined influence of several mineralogical constituents. A strong inverse correlation was identified between compressibility and shear strength (Cc-Cuu: r = -0.67; Cc–ɸuu: r =-0.65). Plasticity is positively correlated with clay content (r ≈ 0.30) and negatively correlated with quartz content (r = -0.44). Calcite improves mechanical strength and bearing capacity (Cuu: r = 0.43; ɸuu: r = 0.34; PL*: r = 0.29), while organic matter increases compressibility (r = 0.34) and reduces cohesion (r = -0.44) and consolidation efficiency (Cv: r = -0.42). Multivariate analysis reveals a tripartite control exerted by clay minerals, carbonates, and organic matter. These results provide a useful basis for the geotechnical evaluation of clay soils in North Africa.