Sensitivity Analyses

A GeoStudio user commented on an earlier post (”solving in batch mode”) asking how to generate thousands of similar analyses that differ only by some input parameters.

Interesting question, and I’d like to hear more about what it is he’s trying to accomplish.  But in the meantime here are some thoughts.

Sensitivity

In SLOPE/W, take a look at the Sensitivity analysis (KeyIn Analyses - FOS Distribution - Sensitivity).

That will let you specify a range of values for certain properties (such as C, Phi and Unit Weight in the material properties), and will re-run the analysis many times.

In Contour you can then do things such as graphing how the FOS is affected by varying Phi. (In the menu that’s Draw - Sensitivity.)

Probability

Similarly you can do a Probabilistic analysis in SLOPE/W, where Solve takes care of varying the parameters in a random way using a distribution function you define. It then gives you a probability of failure instead of a factor of safety.

You can find an example of sensitivity and probabilistic stability analyses on the geo-slope.com web site.

Add-Ins

The other products (Seep, Sigma, etc) do not have sensitivity analyses built in.  (It’s a feature we’re considering adding, so email or leave a comment to cast your vote if you would use it.)

I could imagine doing something similar using an Add-In and a batch file. The batch file could make many copies of the file, giving each a unique name (”dam-1.gsz”, “dam-2.gsz”, etc), then solving each. An Add-In function would be used to specify the property you want to vary. The Add-In would look at the file name (the “1″ or “2″ part of it) to return a different value for each run.

Not a particularly elegant solution, but it would do the trick. Of course you’d end up with hundreds of files and no simple way to compare results or graph results across the varying parameter as you can do in Slope.

Add-Ins are beyond the scope of what I can go into today, but I have been wanting to delve into them on the blog at some point. Let me know if that would interest you.

XML

An even more adventurous route would be to edit the xml inside a gsz file.  (I mentioned in passing in a few other posts that a .gsz is just a zip file that contains a bunch of other files–one of the xml files it contains is what actually defines all the data in your model.)  The advantage would be you could avoid having thousands of files and instead have just a few files each containing a number of analyses.  That lets you share data (so that moving a point in one file wouldn’t have to be duplicated to all the others), and you may also be able to take advantage of the fact that GeoStudio can graph across analyses.

But editing the xml is not something we officially support, so you’re on your own if you choose that route.

I’m curious what it is you’re doing with your thousands of files. Can you share some more detail? Do the tips I mentioned help? We’re working full-force on the next version of GeoStudio at the moment, so this is a great time to hear about features that would be important to you.