A unified damping ratio-based model for cyclic mobility simulation of soils and its application to nonlinear site response analysis

Damping ratio and cyclic mobility are critical dynamic properties of soils subjected to cyclic loadings, while few attempts have been devoted to simultaneously simulating them in practical cyclic models. Based on two phenomenological principles, this paper proposes a unified damping ratio-based hyperbolic cyclic model for simulating the cyclic mobility of soils, specifically addressing the coupled effects of damping and modulus degradation. This model offers distinct advantages over existing cyclic models with fewer model parameters and no requirement for unconventional soil character data. The two model parameters are directly derived from the shear modulus reduction curve and damping curve, which are necessary for all nonlinear dynamic problems in practice. Torsional shear test (TS) and dynamic triaxial shear test (DTS) are conducted on saturated Toyoura sand to validate the proposed model, with experimental data demonstrating its capability to simulate both damping ratios and S-shaped cyclic mobility behavior in cohesive (silty clay) and cohesionless soils (saturated sand). The implementation of the proposed model into site response analysis demonstrated its practical values by accounting for cyclic mobility with minimal model parameters and conventional soil characterization data, while simultaneously simulating the prescribed shear modulus reduction curve and damping ratio curve. These findings establish the unified damping ratio-based model as a superior alternative to existing nonlinear formulations, with potential applications in seismic site response or soil-structure interaction analysis in marine environment.