The Effect of Dynamic Response Characteristics in Different Confining Pressures of Damping Ratio and Shear Modulus of Sandy Soil

Abstract This study investigates the influence of confining pressure on the small-strain shear modulus and damping ratio of sandy soil through cyclic direct simple shear laboratory tests. Undisturbed sandy soil samples were collected from Ibagwa, Nigeria and tested under isotropic confining pressures ranging from 100 kPa to 400 kPa. Shear modulus and damping ratio were measured as a function of shear strain at each confinement level. The results showed that the small-strain shear modulus (Gmax) increased significantly with rising confining pressure, indicating that shear modulus exhibited clear pressure-sensitive behavior. In contrast, the maximum damping ratio (Dmax) was found to decrease progressively with increasing confining pressure. These trends were consistent with established theoretical understandings. Experimental stress-strain data correlated reasonably well with common shear modulus and damping degradation models, validating their predictive capabilities. The pressure-dependent nature of Gmax and Dmax provided fundamental insights into the dynamic behavior of sandy soils under varying effective stress conditions representative of different burial depths. Quantifying these evolving small-strain properties offered essential input parameters for numerical modeling of seismic wave propagation and site response analysis. Understanding variable shear modulus and damping ratio also aided performance-based evaluation of energy dissipation capacity and cyclic loading effects on foundations. The trends demonstrated reinforced the need for geotechnical earthquake engineering analyses and designs to consider changing soil properties relative to stress state - an important knowledge gap addressed. Overall, the study contributed valuable measured dynamic parameters and highlighted the significance of confining pressure in governing the seismic response characteristics of sandy soil.