Small-strain stiffness of in situ granite residual soil: Experimental comparison under biased and isotropic consolidation

Abstract

In this study, granite residual soil (GRS) was subjected to resonant column testing under both biased and isotropic consolidation, and the microstructure of GRS samples under different consolidation modes and stress conditions was examined using scanning electron microscopy. The dynamic shear modulus (G) of GRS increases with increasing effective confining pressure (σ₀') under both isotropic and biased consolidation, while the damping ratio (D) is less affected by σ₀'. With increasing shear strain (γ), both G and D exhibit a stepwise decreasing or increasing trend. There exists a threshold shear strain (γ_th) in the G–γ and D–γ relationships. The increasing trend of maximum shear modulus (G_max) with σ₀' can be illustrated using a double-logarithmic relationship. Compared with GRS soil samples under isotropic consolidation, those under biased consolidation demonstrate higher G_max, G, and γ_th. The normalized distribution range of the G/G_max attenuation curve with γ for GRS is smaller under biased consolidation. Additionally, the rate at which G/G_max attenuates with γ is faster, and σ₀' has less impact on G/G_max. The pore content of GRS under biased consolidation is lower than that under isotropic consolidation, but the proportion of small pores is significantly increased. The variation in GRS microstructure can account for the small-strain stiffness characteristics of GRS samples under different consolidation modes and stress states. These results can provide data support for the refined design and prediction of engineering deformations in areas with residual soil deposits, and offer parameter reference for the numerical analysis of related projects.