Influence of inherent anisotropy on the mechanical properties of normally consolidated clays with a wide range of plasticity indices

Abstract

Inherent (fabric) anisotropy is one of the most important properties of earthen materials that significantly influences their strength and stiffness characteristics. In this study, a comprehensive series of unconfined and constrained compression tests is performed on normally consolidated (NC) clay samples with different plasticity indices to examine the effect of inherent anisotropy on their mechanical characteristics. Accordingly, several cylindrical clay samples with different proportions of kaolinite and bentonite are reconstituted at a wide range of deposition angles, and then subjected to both unconfined and constrained compressive loadings. The experimental results reveal that, for a clay sample with a particular plasticity index, the highest and lowest values of unconfined compressive strength (UCS), secant modulus (E50), and constrained Young's modulus (Eoed) are associated with deposition angles of 0° and 90°, respectively. The results also show that at a certain bedding plane angle, the sample containing 30 % bentonite (PI = 110 %) exhibits the highest UCS, E50, and Eoed values. Several practical empirical correlations are developed to estimate the strength and stiffness properties of NC clays based on their plasticity indices and bedding plane directions. Furthermore, Scanning Electron Microscopy (SEM) analysis is conducted to explore the microstructure of samples containing varying percentages of kaolinite and bentonite.

Keywords

• Bedding plane angle
• Inherent anisotropy
• Plasticity index
• Unconfined compressive strength
• Secant modulus
• Constrained Young's modulus