Seepage

1. 14 SEEP/W
Excess Pore-Water Pressure
SEEP/W can also be used to model the dissipation of excess pore-water pressure. A typical
case is the dissipation of pore-water pressure in an embankment after drawdown of a reservoir.
Consider the case in Figure 1.4. A steady-state condition may have been reached after some
time and then the reservoir is suddenly emptied. SEEP/W’s saturated/unsaturated formulation
makes it possible to analyze the dissipation of the excess pore-water pressure. Note the flow
out of the embankment in Figure 1.4.
The capability of modelling the dissipation of excess pore-water pressure also makes it possible to
perform consolidation analyses. This is discussed later in this chapter in the section entitled Product
Integration.
Figure 1.4 Dissipation of Excess Pore-Water Pressure in an Earth Dam After Reservoir
Drawdown
Transient Seepage
Another large class of problems that can be analyzed using SEEP/W is transient seepage. SEEP/W can
account for the drainage of water from soil pores, or water filling soil pores, and the changes in hydraulic
conductivity that occur in a transient seepage flow system. Examples of transient analyses are illustrated
in Figures 1.5 and 1.6. Figure 1.5 shows the migration of the wetting front through and earth dam after
reservoir filling while Figure 1.6 shows the changing position of the phreatic surface after reservoir
drawdown.
Figure 1.5 Transient Wetting Front Migration Through an Earth Dam After Reservoir
Filling

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Figure 1.6 Movement of Phreatic Surface in an Earth Dam After Reservoir Drawdown
The SEEP/W capability of accommodating both saturated and unsaturated flow makes it a very powerful
tool for analyzing almost any kind of seepage problem you may encounter.
Features and Capabilities
User Interface
Problem Definition
CAD is an acronym for Computer Aided Drafting. GEO-SLOPE has implemented CAD-like
functionality in SEEP/W using the Microsoft Windows graphical user interface. This means that defining
your problem on the computer is just like drawing it on paper; the screen becomes your "page" and the
mouse becomes your "pen." Once your page size and engineering scale have been specified, the cursor
position is displayed on the screen in engineering coordinates. As you move the mouse, the cursor
position is updated. You can then "draw" your problem on the screen by moving and clicking the mouse.
The following are some of the model definition interface features:
· Display axes, snap to a grid, and zoom.
To facilitate drawing, x and y axes may be placed on the drawing for reference. Using the mouse, axes
may be selected, then moved, resized or deleted. For placing the mouse on precise coordinates, a
background grid may be specified. Using a "snap" option, the mouse coordinates will be set to exact
grid coordinates when the mouse cursor nears a grid point. To view a smaller portion of the drawing, it
is possible to zoom in by using the mouse to drag a rectangle around the area of interest. Zooming out
to a larger scale is also possible.
· Sketch graphics, text and import picture.
Graphics and text features are provided to aid in defining models and to enhance the output of results.
Graphics such as lines, circles and arcs, are useful for sketching the problem domain before defining a
finite element mesh. Text is useful for annotating the drawing to show information such as material
names and properties among other things. A dynamic text feature automatically updates the project
information text on the drawing whenever the project information is changed. This ensures that the
project information shown on the drawing always matches the project settings used in the model.
The import picture feature is useful for displaying graphics from other applications in your drawing.
For example, a cross-section drawing could be imported from a drafting application for use as a
background graphic while defining the problem domain. This feature can also be used to display things
like photographs or a company logo on the drawing. Pictures are imported as a Windows metafile
(WMF), an enhanced metafile (EMF), or a Windows bitmap (BMP).
Using the mouse, individual or groups of graphics and text objects may be selected, then moved,
resized or deleted.

3. 16 SEEP/W
· Graphical finite element mesh generation and editing.
After the problem has been sketched, the problem domain must be discretized into a finite element
mesh. To facilitate this, quadrilateral and/or triangular regions are drawn in the problem domain. Inside
each region, any number of finite elements can automatically be generated. Individual or groups of
nodes and elements may be moved or deleted using the mouse to select and drag these objects. The
figure below shows how a quadrilateral region is interactively meshed with quadrilateral elements.
· Graphical application of soil types and boundary conditions.
Each element in the mesh must be associated with a soil type. This can be accomplished using the
mouse to select individual or groups of elements to which a soil type will be assigned. Boundary
conditions can also be assigned to nodes and edges using the mouse. The figure below shows the
application of a fixed 0.3 m total head boundary condition being applied to node 10.

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· Graphical and keyboard editing of functions.
SEEP/W makes extensive use of functions. For example, boundary conditions can be a function of
time, and hydraulic conductivity is a function of pore-water pressure. All these functions can be edited
graphically using the mouse and exact numerical values can be input using the keyboard. The figure
below shows a point on a conductivity function being moved using the mouse.

5. 18 SEEP/W
· Graphical flux section definition.
It is often of interest to compute seepage fluxes across some section of the problem domain. Multiple
flux sections can be drawn through the problem domain using the mouse.
· Graphical initial water table definition.
For transient analyses, initial conditions are required. The fastest way to specify initial conditions is to
draw the water table across the problem domain, which can be done using the mouse.