Dynamic modulus and damping ratio of organic-matter-disseminated sand under cyclic triaxial condition

In Hainan Province, China, the unique geographical location presents significant challenges to the safety of coastal infrastructure due to complex dynamic loads such as waves, sea breeze and earthquake. A type of organic matter-rich and poorly graded organic-matter-disseminated sand (OMDS) is commonly found in this region. The existence of OMDS can reduce the bearing capacity of composite foundation and may even lead to structural failure. Currently, there is insufficient understanding regarding this type of sand. This article characterizes the dynamic parameters of OMDS through dynamic elastic modulus (E_d) and damping ratio (λ). A series of undrained cyclic triaxial shear tests were carried out on OMDS specimens with varying compaction energy, initial confining pressure and consolidation ratios. Based on these experiments, a modified Hardin-Drnevich model is presented to explain the dynamic constitutive relation. Furthermore, the impacts of compaction energy, initial confining pressure, and consolidation ratio on skeleton curve, E_d, normalized dynamic elastic modulus (E_d/E_dmax) and λ are systematically discussed. The results show that dynamic axial stress (σ_d), E_d, E_d/E_dmax and λ are all proportional to the compaction energy; lower compaction energy results in earlier stiffness deterioration. As confining pressure increases, σ_d and E_d rise, while λ decreases, with E_d /E_dmax being less affected. Finally, empirical models with respect of the varied parameters are proposed to estimate the maximum dynamic elastic modulus (E_dmax) and maximum damping ratio (λ _max), yielding relatively accurate estimation results. This study provides new insights into the dynamic properties of bay facies sand enriched with organic matter, which may facilitate the design and application of this type of sand in coastal projects.