Product: GeoStudio – SEEP/W
Occurrence:
I am setting up my material properties in SEEP/W and am unsure of which material model to use.
Resolution:
The position of the water table is often not known before solving a seepage analysis. The position of the water table may also change over time during a transient analysis. Thus, any materials that may have both saturated and unsaturated conditions during a steady-state or transient analysis require the use of the saturated/unsaturated material model. The saturated/unsaturated material definition involves the specification of functions for the volumetric water content and hydraulic conductivity with changes in pore water pressure – specifically in the negative pore water pressure range, as negative pore water pressures are associated with unsaturated conditions.
If a saturated-only material model is applied to a region exhibiting both saturated and unsaturated conditions, the seepage results produce unreasonable flows in the unsaturated zone (as illustrated in the first image below). When the saturated/unsaturated material model is applied to this same region, there is still some flow occurring in the unsaturated zone (groundwater flow can still occur in the unsaturated zone), but it better represents the decrease in flow due to lower volumetric water contents and the corresponding decrease in hydraulic conductivity (as illustrated in the second image below).
Notes:
In cases where saturated flow is dominant (as in the illustrated example here), it is important to define the hydraulic functions to limit flow in the unsaturated zone. However, the exact shape of the functions is less important. Thus, an estimation of the hydraulic functions is all that is necessary.