Is there a movement toward three-dimensional slope stability analyses?

Over the past few years, interest in performing three-dimensional (3-D) slope stability analyses has surged. An increasing number of research papers on this topic are being published at conferences and in peer-reviewed geotechnical journals. This increased interest has resulted in a reconsideration of the fundamental issues surrounding 3-D analysis and its practical application in the geotechnical consulting industry. Landslides and most mass movements are, in general, 3-D in character. However, it has been common practice to analyze the sliding mass by considering static limit equilibrium conditions on a two-dimension (2-D) slice through the zone of greatest depth. Some questions that a geotechnical engineer might ask when considering the relationship between 2-D and 3-D slope stability analyses are:

• Is there a need to perform a 3-D analysis in most situations where slope instability is a concern?
• What role do geometry and stratigraphy play in arriving at the conclusion that a 3-D slope stability analysis should be performed?
• In the case where a slope has failed, what is the relationship between performing a back-analysis and a forward analysis, while using a 2-D analysis on a mass movement that is obviously 3-D in character?

This article attempts to address these questions while also trying to assess whether 3-D aspects should play a significant role in the engineering design, or if they are now being considered simply as the natural outgrowth of having increased computational tools.