Numerical Modeling of Consolidation Processes in Hydraulically Deposited Soils

Nicholas Robert Brink, University of Colorado Boulder


Hydraulically deposited soils are encountered in many common engineering applications, including storage of mine tailing in tailing storage facilities (TSFs), hydraulic dredging operations and geotextile tubes filled with slurries. Consolidation settlement of these slurry materials is often of interest to geotechnical and mining engineers, as these materials may undergo significant volume change under the influence of relatively small stresses. The consolidation process for hydraulically deposited soils is highly nonlinear, as the soil compressibility and hydraulic conductivity may change by several orders of magnitude. Classical consolidation theory, which assumes that the material properties remain constant throughout consolidation, clearly cannot be applied to such highly compressible soils. Instead, numerical techniques are often required.

Several commercially available finite element codes poses the ability to model soil consolidation, and it was the goal of this research to assess the ability of two of these codes to model the large-strain, two-dimensional consolidation processes which occur in hydraulically deposited soils. For this research, the codes ABAQUS and PLAXIS were chosen due to their market availability and their common use by geotechnical engineers.

First, a series of one-dimensional consolidation models was created with the goal of verifying the ability of these codes to model large-strain consolidation. Results were compared to solutions given by the finite strain theory developed by Gibson et al. (1967). Solutions to the Gibson equation were derived using a custom finite difference code titled CONDES. Several limitations to the ABAQUS and PLAXIS codes were discovered during this process, including the existence of a minimum initial effective stress below which numerical solutions become unstable. Then, with the ABAQUS and PLAXIS codes having been verified, a series of rectangular models were created in which seepage was allowed both vertically and horizontally. These models were created to represent two-dimensional drainage scenarios without including the full complexities of more realistic and irregular geometries. With the successful creation of these two-dimensional numerical models, more realistic scenarios were then modeled including a geotextile tube filled with fine-grained slurry and a tailing storage facility in which tailing is deposited as a slurry.