Piecewise-Linear Formulation of Coupled Large-Strain Consolidation and Unsaturated Flow. II: Testing and Performance

Abstract

A piecewise-linear formulation for simulating coupled large-strain consolidation and unsaturated flow using a mass-conservative and noniterative solution was developed in a companion paper and implemented in a proposed program called UNSAT-CON. The formulation is tested in this paper using numerical cases as well as laboratory and field data. First, UNSAT-CON is tested by comparing model predictions to published predictions of a finite-element-based model that uses a quasi-unsaturated formulation to model evaporation: the same quasi-unsaturated formulation is implemented in UNSAT-CON to allow direct comparison. Excellent agreement of settlement over time for various levels of evaporation are obtained. UNSAT-CON reliably predicts the hydraulic exchange at the soil–atmosphere interface under the conditions of evaporation, decantation, or their combinations. The fully unsaturated formulation is tested on fine-grained tailings by calibration with a documented laboratory column test and verification with a 4.1-m-deep field trial. This testing exercise showed (1) three-dimensional (3D) constitutive surfaces are largely constrained when defined using conventional test data such as the saturated compressibility function and soil water characteristic curve; (2) good to excellent agreement between measurements and predictions are observed, including the developing suction, decreasing void ratio, increasing solid content, and increasing settlement rate due to evaporation effect on the near surface zone; and (3) modeling desaturation allows for a more-realistic simulation of deformation in the unsaturated zone than using formulations that do not model desaturation.