Shear Stress-Strain Curves Based on the G/G_max Logic: A Procedure for Strength Compatibility

Hyperbolic models are frequently used in practice to represent nonlinear shear stress-shear strain behavior of soils in equivalent linear and nonlinear dynamic modeling problems. Several researchers have proposed shear modulus reduction (G/G_max versus \xg) curves that use the hyperbolic model as their basis, with parameters that fit the models to cyclic laboratory test results. However, cyclic laboratory tests often are not run to failure shear stress levels. Consequently, the model G/G_max curves are well constrained by the data at small-to-moderate shear strains, but do not necessarily provide an accurate representation of soil strength at large shear strains. In some cases, the shear strength can be grossly inaccurate, which may result in significant errors for analyses involving shear stress levels at or near failure. In this paper, a new hybrid methodology is presented that permits simultaneous matching of: 1) the conventional shear modulus reduction curves that are well calibrated at small-to-moderate shear strains and; 2) the soil shear strength at large strain. This hybrid approach produces shear modulus reduction curves that result in corresponding, hyperbolic-like, smooth, stress-strain, backbone curves. These curves assure that the soil shear strength consideration is accurately represented for the purposes of both equivalent-linear and nonlinear analyses.