Development and Implementation of a Constitutive Model for Unsaturated Sands

The development and implementation of a constitutive model used to predict the behavior of unsaturated sands are described. The model is based on critical state and bounding surface concepts and incorporates parameters to account for sand fabric and suction. The model was implemented into finite-element software using user-defined mechanical material behavior (UMAT) subroutine. The model performance was verified with a wide range of triaxial test data that included different drainage conditions, sample preparation methods, densities, confining stresses, and modes of shear. Simulation results show that saturation level significantly affects sand performance and a modified suction-based state parameter is proposed to describe better such sand behavior. This parameter was found to correlate well with an increase in peak stress caused by a decrease in saturation level. (C) 2017 American Society of Civil Engineers.