Investigation of Shear Modulus and Material Damping of a Lightly Cemented Silty Sand Representing Offshore Soil

Offshore structures remain highly relevant, making the dynamic characterization of offshore soils critical. Since many offshore soils are cemented, understanding their response to dynamic loads is essential for developing accurate models that improve the reliability and cost-effectiveness of offshore structure designs. This study examines the impact of cement content on shear modulus, shear modulus reduction, shear wave velocity, and material damping of lightly cemented fine silty sand. A series of Resonant Column and Torsional Shear tests were conducted. The results were analyzed and compared to existing literature. The modified hyperbolic model was proposed to characterize the shear modulus and damping behavior, and the model parameters were determined. The findings indicate that an increase in cement content reduces the linear threshold strain of the material for both shear modulus reduction curves and damping curves. This behavior continues until a threshold cement content is reached. Beyond this, the linear threshold strain begins to increase, making linear threshold strain the point where cemented soils are most brittle under shear. This threshold cement content likely varies with soil type. Cement content significantly increases maximum shear modulus but was found to impact on minimum damping. The nature of the increase in shear modulus is related to threshold cement content. In addition, 57 offshore soil samples from Long Bay, North Carolina and South Carolina were characterized, generally identified as sands with significant fines, cement, and/or shell contents. As an example of possible application, the proposed modified hyperbolic model parameters were used to generate shear modulus reduction curves for two representative soils from Long Bay, North Carolina and South Carolina.