Hyperbolic hydro-mechanical model for seismic compression of unsaturated sands in the funicular regime

A semi-empirical model with a hyperbolic shear stress–strain curve was developed to predict the seismic compression of unsaturated sands in the funicular regime during undrained cyclic shearing. Plastic volumetric strains obtained from hyperbolic plastic shear strains with a flow rule were used to calculate changes in degree of saturation from phase relationships and changes in pore air pressure from Boyle’s and Henry’s laws. The calculated degree of saturation was used to estimate changes in matric suction from transient scanning paths of the soil–water retention curve. The shear modulus was updated from corresponding changes in mean effective stress, affecting the hyperbolic stress–strain curve’s shape. The model was validated using data from undrained cyclic simple shear tests on unsaturated and dry sand specimens. While the model captured trends in hydro-mechanical variables in the funicular regime as a function of shearing cycles well, it underestimated the measured volumetric strain at large numbers of cycles in some tests. An increasing–decreasing trend in seismic compression with initial degree of saturation was predicted from the model with a peak seismic compression at low degrees of saturation. Discrepancies with data may be due to not considering post shearing reconsolidation at higher degrees of saturation and experimental variations.