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

• Effect of inherent anisotropy on mechanical properties of normally consolidated clays is examined. • Unconfined and constrained compression tests are performed on NC clays with various PI values. • Unconfined compressive strength, secant modulus, and constrained stiffness of samples are assessed. • The sample containing 30% bentonite ( PI = 110%) exhibits the highest UCS, E 50 , and E oed . • Microstructural analysis is conducted on clays with various plasticity indices and deposition angles. Inherent (fabric) anisotropy is one of the most important properties of earthen materials which has a significant influence on 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. According to the experimental results, for a clay sample with a particular plasticity index, the highest and lowest values of the unconfined compressive strength ( UCS) , the secant modulus ( E 50 ), and the constrained Young's modulus ( E oed ) are observed to be associated with the deposition angles of 0 o and 90 o , respectively. The results also show that at a certain bedding plane angle, the sample containing 30% bentonite ( PI = 110%) exhibits the highest UCS, E 50 , and E oed values. Several practical empirical correlations are developed to estimate the strength and stiffness properties of NC clays using their plasticity indices and bedding plane directions. Scanning Electron Microscopy ( SEM ) analysis is also conducted to explore the microstructure of samples containing varying percentages of kaolinite and bentonite.