Modulus degradation characteristics of saturated marine coral sand under anisotropic consolidation and various loading frequencies

Abstract

Marine coral sand is a primary fill material for port and infrastructure construction on coral islands. When embedded in slopes and embankments, it is typically in an anisotropic consolidation and saturated state. A series of undrained cyclic shear tests with various loading frequencies (f) were conducted on saturated coral sand in an anisotropic consolidation state (consolidation stress ratio, k_c, and consolidation direction angle, α_c). When the 90° jump of loading principal stress path with the cyclic loading direction angle (α_σ) of 22.5°is applied, all strain components exhibit significant development, generalized dynamic modulus (K) replaces Young's (E) or shear modulus (G) as the suitable physical index for characterizing the global stiffness. Specimens under anisotropic consolidation persist residual generalized dynamic modulus (K_r) even in the failure phase. K_r increases with increasing k_c and f, and decreases negatively exponentially as α_c increases. The maximum generalized dynamic modulus (K₀) is significantly influenced by anisotropic consolidation state and f. The effect (positive or negative) of the anisotropic consolidation state is determined by α_c, and it is nonmonotonic from α_c = 0° to 45° The increase of k_c only serves to strengthen the effect of α_c on K₀. Additionally, K₀ and f exhibit a strong logarithmic correlation, which is independent of anisotropic consolidation state. Ultimately, relative generalized dynamic modulus (η) is introduced to characterize the decline characteristic of K, and a generalized Davidenkov model which normalized consolidation conditions and f is established over a wide strain range.