Small-Strain Stiffness Properties of Fissured Clay with Different Fissure Orientations

In geotechnical engineering, the small-strain shear modulus and its attenuation characteristics are pivotal for analyzing and evaluating soil vibration responses to various engineering construction projects. This study conducts the resonant column test on undisturbed fissured clay samples, exploring the impacts of fissure inclination and confining pressure on the shear modulus in small-strain range. Results indicated that the shear modulus and its attenuation behavior in undisturbed fissured clay are substantially affected by both the fissure inclination angle and the confining pressure. With constant confining pressure, the shear modulus increases as the fissure inclination angle grows, reaching its maximum value at a fissure angle of 90°. In addition, as the confining pressure rises, there is a notable increase in the shear modulus and a corresponding reduction in the decay rate. Through the threshold strain, the elastic deformation of the specimen increases as the fissure inclination angle increases, and the confining pressure increases the ability of the fissured soil to deform at small strains elastically. Based on the acquired data, this research analyzes the relationship between the fitting parameters $A$ and $N$ and the fissure angle in the context of the Harding–Drnevich formula. Consequently, a mathematical model based on the fissure inclination angle and the effective confining stress was established to predict the maximum dynamic shear modulus ($G_{\max }$) and decay attributes of undisturbed fissured clay. Additionally, the study offers a comparative analysis of the maximum shear modulus and its attenuation features in clay with varied degrees of fissure development. The stiffness anisotropy is related to the orientation of particles and the normalized decay rate of the fissured clay has a certain relationship with the fissure density.