Modeling of soil deformation and water flow in a swelling soil

Soil deformation and unsaturated transient water flow in swelling soil on a laboratory scale is predicted using a one-dimensional numerical model. The model is based on a soil water flow equation and extended to soil deformation using Lagrangian description (LD). The specific features of the model are inclusion of an overburden component in the total potential of the flow equation, introduction of a shrinkage-swelling characteristic (SSC) known as a third soil hydraulic function, and two-dimensional analysis of soil deformation using a geometry factor. This paper describes an evaluation of the model, which was previously verified with a case of shrinkage of marine clay soil, with a data set from an infiltration experiment performed under swelling conditions. Soil hydraulic properties such as moisture retention characteristic (MRC), hydraulic conductivity function (K(h)) and SSC were derived from simultaneous measurement of volumetric moisture content (VMC), bulk density and pressure heads in a framework of the Eulerian description (ED). Two different K(h) relationships, with respect to moving solid particles, were obtained from both the LD and ED. Simulation was performed using two different hydraulic conductivities, i.e., Eulerian descriptive hydraulic conductivity (EDHC) and Lagrangian descriptive hydraulic conductivity (LDHC). Model performance was evaluated using four different statistical parameters representing the goodness of model predictions on the transient variations of soil moisture contents. Results of the evaluation reveal that the model predicts reasonably well the moisture content changes, although the use of LDHC gives slightly better results than the EDHC. Overprediction of moisture contents by the simulation model especially near the bottom of the sample is attributed to the incomplete dissipation of swelling pressure during expansion of the soil material. As a result, the soil shows anisotropic swelling although it was forced to deform in the one-dimensional vertical direction by experimental design. Unlike other one-dimensional consolidation models, the model can be used for two-dimensional analysis of soil deformation in porous media with either self-weight or external load application, at either shrinking or swelling phase and under both saturated and unsaturated flow conditions.