Nate Hekman has been a software developer with GEO-SLOPE International since the days when only two developers worked on the user interface of what is now branded GeoStudio 2007.  His passion is to make the software so easy to use you don’t even think about it, but until that day comes, he’s happy to share insider tips and tricks on his blog, Grokking GeoStudio (and the occasional article on GeoPrac.net!).

[Editor] In geotechnical engineering practice we most commonly look at a single set of conditions to anlalyze for a slope stability analysis. In many cases, this is an acceptable approximation of reality. But there are certain times where changing pore water pressures or stress states may warrant a more detailed analysis, a time-dependent stability analysis or transient analysis. In this article, Nate discusses transient stability analyses with SLOPE/W 2007. At the end of the article, he refers the reader to a downloadable example problem for a rapid drawdown condition in both PDF and GSZ (GeoStudio 2007) format. We look forward to more GeoPrac.net contributions from Nate in the future! [/Editor]

Transient Stability Analyses with SLOPE/W 2007

By Nate Hekman
Software Developer, GEO-SLOPE International Ltd.

Introduction

SLOPE/W 2007 is one of a family of eight products produced by GEO-SLOPE International, together referred to as GeoStudio 2007.

One of the strengths of this software suite is how every product can integrate with every other. SLOPE/W, for example, can be used quite well on its own to analyse slope stability. But it can also get the pore water pressures in the soil from SEEP/W, look at the reaction of a slope to an earthquake with QUAKE/W, or any number of other combinations.

This article will examine how to look at changes to slope stability over time by using the results of another transient analysis as input.

In Theory

The theory behind transient stability analyses is fairly simple. A typical "static" SLOPE/W analysis calculates a factor of safety for a specific snapshot in time. You determine what that snapshot is by identifying a finite-element analysis and a time step to use for the current pore-water pressure and/or stress conditions.

A transient stability analysis simply performs the same calculations over and over at several successive snapshots in time.

In Practice

To perform a single stability analysis (at a single point in time) you have always been able to use KeyIn Analyses to pick another analysis from which to obtain pore water pressures or stress conditions. You identified the other analysis and the time step to use. The stability analysis would give you a factor of safety for that snapshot in time.

For a transient stability analysis you choose “(all)” as the time step:

When you choose “(all)”, the SLOPE/W solver will repeat its calculations once for each time step it finds in the other analysis. You end up with one factor of safety for each slice in time.

That’s it! That’s all it takes to set up a transient stability analysis.

The fun of course starts when you can look at the results.

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