To investigate the dynamic properties of deep silty clay, a comprehensive set of cyclic triaxial and resonant column tests were performed on undisturbed samples of silty clay containing sand from depths reaching 54.5 m in Shanghai. This study aimed to characterize the influence of confining pressure on the stress–strain behavior, pore water pressure, and dynamic modulus of the soil. The present findings revealed that the confining pressure, which is correlated with the depth of burial, significantly influenced the soil deformation. Moreover, elevated confining pressures resulted in increased stress within the hysteresis loops, a higher initial shear modulus, and a diminished ratio of excess pore water pressure. Based on the empirical data, a refined model was formulated for the shear modulus and damping ratio as functions of the shear strain for deep silty clay in Shanghai. These insights are intended to offer a robust reference point, facilitating calibration and guiding subsequent investigations into structures situated in the deep subterranean environments of Shanghai.