Transient Stability Analyses with SLOPE/W 2007


The simplest way to look at results is just to pick a specific snapshot in time—a specific time step—and use SLOPE/W CONTOUR just as you do for a single analysis.

You pick the time step from the Analysis toolbar:


If the Time dropdown list has the focus (you can press Alt-I to give it the focus) you can use the Up and Down arrow keys to step through each time step, watching how the critical slip surface and factor of safety change over time.

All the other features of SLOPE/W CONTOUR will work too, like drawing graphs, viewing slice forces, etc. They all show you data for the current time step.

Graphing FOS over Time

To get the bigger picture, try graphing factor of safety over time.

This graph is not under Draw Graph as you might expect. Because you also need to select which slip surface to use, you find this graph under Draw Slip Surfaces:

There are two graphs to choose from:

  • The “Factor of Safety vs Time” graph uses the current slip surface, showing its FOS at each time step. Use this graph if you care about a specific mode of failure.
  • The “Minimum Factor of Safety vs Time” graph ignores the current slip surface, instead showing the FOS of the most critical slip surface at each time step. This graph is useful to see if a slope will be stable over time, at any slip surface.

Sometimes the two graphs will be the same (especially if you’re using the Auto-Locate method or the “optimized” slip surface option, because those are by definition the most critical), but if PWP conditions vary enough over time that at a particular step the critical slip surface is at a different location than at another step, the graphs will be different.

If you are doing a Probability analysis, you will also be able to see graphs of “Probability of Failure vs Time” and “Maximum Probability of Failure vs Time”.


Just as with any transient analysis, you can use the View Movie command to create a movie of the slope analysis. Each time step becomes a frame in the movie. Use Sketch Text fields to add key values that will change over time through the movie, such as the elapsed time and the factor of safety.