Slope with ponded water.pdf - GEO-SLOPE International Ltd.

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for some reason, the warning message will not appear. Please note that pressure lines are now referred to
as surcharge loads in Version 7.1, which is more accurate.
The new approach that has been implemented in Version 7.1 computes the stabilizing weight of the water
acting on the ground surface by looking at the positive pore-water pressures that exist along the ground
surface. This approach will work for piezometric lines, pressure heads defined using a spatial function or
finite element computed heads. The presence of positive pore-water pressures on the ground surface line
will be visually represented by a shaded area showing the extent of the ponded water and with arrows
indicating the direction that the water force will be acting on the free body. Water forces will act normal
to the ground surface line.
Pore-water pressures at the base of each slice will be computed differently depending on the method used.
For piezometric lines, the vertical distance from the base of the slice up to the relevant piezometric line
multiplied by the unit weight of water as defined under SET: Units and Scale, will determine the porewater
pressures that exist at the base. For pressure heads developed using a pressure head spatial function,
the pore-water pressures will be determined using a numerical process called Kriging. For finite element
generated pore-water pressures, the location of the base of the slice, relative to the nearest finite element
nodes, will be determined and the pore-water pressures will be interpolated from the finite element
computed results.
For the example being described in this article, a piezometric line has been created and assigned to both
the foundation and embankment materials. Accordingly, the stabilizing weight of the water will be
applied in the analysis and is represented with a shaded zone and arrows.
3.1 Case 1 – Water layer modeled with a piezometric line
In this case, the ponded water is modeled with a piezometric line. Note that the piezometric line is drawn
across the anticipated surface of the ponded water where pressure equals zero (P = 0). The area between
the ground surface line and the piezometric line has been shaded to indicate the extent of positive porewater
pressures and arrows have also been painted along the ground surface to indicate the direction that
the water force is acting.
The global unit weight of water under SET: Units and Scale has been defined as 9.807 kN/m 3 as shown in
Figure 2. This is the value that will be used together with the vertical height of the piezometric line to
compute the correct pore-water pressure at the base of each slice. This is also the unit weight that will be
used to compute the water force acting on the ground surface. If you want to use a different value, you
can change the global value and then do a quick hand-calculation to confirm to yourself that the unit
weight being used is what you have input.
SLOPE/W Example File: Slope with ponded water.doc (pdf) (gsz) Page 2 of 7