A framework-based finite element approach for solving large deformation problems in multi-phase porous media.

Abstract

The performance of the uniform gradient element formulation is studied by simulating settlement of a footing and dynamic behavior of a saturated clay embankment and a level ground. Significant hourglassing is seen for the footing problem when the uniform gradient elements were used without any hourglass control. The hourglass modes triggered by the stress gradients underneath the footing were found to propagate in all directions. The proposed hourglass control scheme is shown to be effective in controlling the excitation of hourglass modes. It is also found that for the dynamic problems that involves only body forces very little hourglassing was seen even when uniform gradient elements were used without any hourglass controls. The solid stiffness and solid damping hourglass control parameters show minor impact on displacement and pore pressure time histories. On the other hand, the fluid stiffness parameter shows significant influence on the displacement and pore pressure time histories. From the parametric study on the fluid stiffness hourglass control parameter, it is recommended that this parameter should be less than 0.1%.

In the finite element simulation of dynamics of porous media, governing equations are derived and solved assuming that the material undergoes small deformation. However, liquefaction induced ground deformation and wetting induced slope failures are a few examples of large deformation problems. Therefore, large deformation analysis is required to correctly predict the behavior of porous media. A large deformation theory is developed for the saturated and unsaturated porous media and implemented within the TeraScale framework. The dynamic behavior of saturated and unsaturated porous media is studied using both small and large deformation analyses. The analyses show that the settlements are over predicted by small deformation analysis compared to the large deformation analysis.

A new high performance computational tool has been developed to analyze the static and dynamic behavior of saturated and unsaturated soils. The new tool is developed using a parallel finite element framework from TeraScale, LLC and is named TeraDysac. The TeraDysac is capable of running on multiple processors. The current version has been successfully tested on a two-processor machine.

The full formulation and a reduced formulation for unsaturated soils are implemented within the TeraScale framework. A centrifuge shaking experiment on unsaturated low permeable Minco Silt is simulated using both full and reduced formulations. It has been found that the reduced formulation predicts the dynamic response of the unsaturated Minco Silt embankment reasonably well. The reduced formulation is computationally very efficient. Therefore, it can be concluded that the reduced formulation is sufficient to predict the dynamic behavior of unsaturated Minco Silt. (Abstract shortened by UMI.)