Utvärdering av programvaror för numerisk simulering av negativa portryck

Sammanfattning: Pore water pressure is defined relative to atmospheric pressure and it is cero kPa at the water table. Under the water table the pore water pressure rises linearly at a hydrostatic pressure distribution and above the water table it sinks. How the pore water pressure profile above the groundwater table develops in practice depends on the soil water content. The relationship between water content and pore pressure is not linear. It is described by a water content curve(wcc) or water retention curve. There are several different models to mathematically describe the water retention curve. Two of the most common models are developed by van Genuchten (1980) and Fredlund and Xing (1994). There are a variety of software programs that can perform simulations of ground water motions. However, there are relatively few software programs that perform calculations of water flow above the water table. An inventory has been done here which lists nine software packages that can simulate water flow in unsaturated soils. In this report three software products, which can simulate negative pore pressure, i.e. perform calculations of water flow in unsaturated soils, have been evaluated and compared. The three software products are SEEP/W (Geostudio), SvFlux (Soilvision) and MidasGTS (MidasIT). The evaluation has been done by designing and calculating the same models in the various programs. The models were constructed as similar as possible in order to compare results and to see the options available to design specific problems in the various programs. Three of the models used are reconstructions of examples presented by Geostudio. A parametric study has also been made for a model used by Rebecca Bertilsson in a previous parametric study (Bertilsson 2010). Attempts have been made to set up and calculate examples in Midas GTS in the same way which has been done in SEEP/W and SvFlux. Working with Midas GTS has been problematic. Midas GTS showed to be difficult to use for calculations of negative pore water pressure. Solutions have not been presented to the same models constructed in SEEP/Wand SvFlux and Midas GTS has subsequently not been covered in the comparison of the programs. The main difference between SvFlux and SEEP/W is the way to construct the FEM mesh. SvFlux is designed with adaptive meshing which automatically changes the mesh as the solution progresses. SEEP/W and SvFlux have shown similar results. Differences in the results usually could be related to differences in meshing and time stepping. Of the two software’s SEEP/W and SvFlux, SEEP/W have been perceived as a more convenient tool for numerical analysis of negative pore water pressures.