Tech Briefs

Soil Consolidation Analysis

We present a typical problem in soil consolidation analysis, in which we compute the distribution of excess pore pressure and the displacement under the applied load for a simple three-layered soil model.

The above animation shows the dissipation of excess pore pressure and the (magnified) displacements of the soil skeleton. In the middle layer (sand), the permeability is high, so the pore pressure is constant. In the upper and lower layers (clay), the permeability is low, so the pore pressure is non-uniform and signficant time is needed for the pore pressure to dissipate. The soil model is shown below in greater detail.

The load is applied instantaneously and is held constant for a period of 295 days.

We use the porous medium formulation of ADINA in the analysis. In this formulation, the soil skeleton is assumed to be fully saturated with water. The unknowns are the displacements and the pore pressure. The water flows through the soil skeleton in accordance with Darcy's law.

The permeabilities of each layer are specified. The surface is modeled with a drained boundary condition (zero pore pressure) and the bottom of the model is modeled with an undrained boundary condition (no pore fluid flow through the boundary).

The soil skeleton is modeled with linear elastic material models. (Other geotechnical material models, such as the Mohr-Coulomb, Cam-clay or Drucker-Prager models, can also be used.)

Although this problem is most efficiently solved with plane strain 2-D elements, we use 3-D elements as a demonstration. 27-node elements are used, with pore pressures defined only at the corner nodes. The analysis is quasi-static and linear.