From stiffness to strength in site response predictions: Formulation and validation of a hybrid hyperbolic nonlinear soil model

Abstract:

Nonlinear site response analyses are becoming an increasingly important component of simulated ground motions intended for engineering applications. For regional-scale problems where geotechnical data are sparse, the challenge lies in computing nonlinear ground deformation to very strong ground shaking using a very small number of input parameters. We have developed a nonlinear model that addresses these issues: it simultaneously captures the soil’s low-strain stiffness and large-strain strength of soil, and yields reliable predictions of soil response to weak and strong shaking using as sole input the shear wave velocity profile. We here present the formulation of the model and an extensive validation study based on downhole array recordings, with peak ground acceleration ranging from 0.01-0.9g. We also show that our model, referred to as hybrid hyperbolic, outperforms existing nonlinear formulations and simplified site response analyses widely used in practice for ground motions that induce more than 0.02% of soil strain (roughly equivalent to PGA higher than 0.02g). In addition to site-specific response predictions at sites with limited site characterization, the hybrid-hyperbolic model can help improve site amplification factors of ground motion prediction equations (GMPEs) by complementing the empirical data with simulated site response analyses for very strong ground shaking; as well as physics-based ground motion simulations, particularly for deeper sedimentary sites with low resonant frequencies.