We are analyzing the saturation and pore pressures in a dry stockpile, where we want to simulate 15 rainy days and 15 dry days. We expected that during the rains a more saturated surface layer would form, and that this surface saturation would decrease during dry days.
We used unsaturated model with 80% of saturation above the water level, groundwater model as Van Genutchen, permeability of 0,086m/day, and precipitatio table with 0,1e-3m³/day. Calculation type is Fully coupled flow.
However, the results are different from what was expected: during the 15 days of rain, the saturation decreases and after the next 15 dry days, the model becomes more saturated, as the images below.
(after 15 days of rain)
(after 15 dry days)
What do we need to change?
The infiltration rate is quite low and seems to balance out the saturation level during the 15 day rain period which is what we see in the first screenshot that the saturation level remains the same at about 80-85%%. Then the 15 day dry period seems to allow the water movement in the unsaturated zone in the upward direction towards the top of the slope because the infiltration boundary has been removed. Sometimes comparing contours may not be the best approach as the colors can be difficult to interpret sometimes. A better approach would be to compare saturation levels at nodes/stress points to get a better idea.
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