GGU-STABILITY: Principles
- Matthias Jusko
Generally, pore water pressures in slopes are defined using a pore water pressure line. The appropriate programs (including GGU-STABILITY) calculate the pore water pressure at the slice foot from the vertical distance between the slice foot and the pore water pressure line directly above it. This procedure implies the supposition that percolation through the slope is exclusively horizontal. This supposition is sufficiently exact for a large number of slopes. With complicated flow conditions (e.g. embankment with exterior seal), this supposition is no longer justified. Consideration of artesian conditions is also only helpful in a few special cases. A correct consideration of complicated flow conditions can therefore only be done if the pore water pressure is defined at every point of the slope. The GGU-STABILITY program allows such a definition via a pore water pressure mesh (triangular mesh), which must cover the whole area of the slope to be investigated. The potential h is defined at each triangle point
h = u/
with
u = pore water pressure, e.g. in kN/m²
w = unit weight of water
y = elevation head
With the help of this triangular mesh the program can determine the pore water pressure u at every point, using linear interpolation within the triangular mesh. You can define this pore water pressure mesh completely with the mouse. This can, however, take some time for complicated flow conditions. If you are in possession of a groundwater program, you can read-in these data as an ASCII file (x, y and h). Reading-in a pore water pressure mesh is especially comfortable if you own the groundwater modeller GGU-2D-SSFLOW. Post-processing is then no longer required.
Example 2 from the Supplement to DIN 4084 (see file DIN4084_Bishop_pwp_02-e.BOE) contains, e.g., the following potential line mesh, which was calculated with GGU-2D-SSFLOW:
If the system does not include complicated flow conditions and defining the pore water pressure via a pore water pressure line is sufficient, you can forego study of the following sections on pwp mesh.