Constitutive Modeling Including Creep- and Rate-Dependent Behavior and Testing of Glacial Tills for Prediction of Motion of Glaciers

Abstract

The disturbed state concept (DSC) is used to characterize the deformation behavior of glacial tills, which may have a significant role in the motion of overlying glaciers with attendant implications for global climate dynamics. The model includes elastic, plastic, and creep deformation; microstructural modifications leading to softening and failure; and effect of rate of loading. This paper also presents a procedure to construct the static yield surface, which is essential to model the full creep response of the material. Laboratory triaxial tests are performed to calibrate the model. Predictions are compared with the test data, which include independent validations. A finite-element (FE) program with the implementation of the DSC model is used to predict the motion of an idealized ice sheet as affected by the deformation in the till. A novel concept is proposed to predict the failure and resulting motion of ice sheets. The concept involves the definition of state in the deforming till when stress, strain, and the disturbance reach critical values beyond the peak stress. The proposed concept is considered to be more realistic than the commonly used Mohr-Coulomb (M-C) criterion, in which failure and motion are assumed to occur at the peak stress with very small (elastic) strains.