Heuristics, biases, and expertise in identifying critical slip surfaces

While various algorithms are available to identify critical slip surfaces in soil slopes, practitioners often need to seed the surface search and validate identified surfaces. Identifying critical slip surfaces requires assessing competing cues related to driving and resisting moments, using heuristic reasoning and intuition. This study received 181 responses to a task asking participants to identify the most and least critical slip surfaces in three different slope stability scenarios. Most participants correctly identified one or two of the highest (mean = 1.6), and, on average, they identified one of the lowest factors of safety (mean = 1.0). Expertise measures only correlated with performance in the scenario with the highest factor of safety across the three scenarios and not the other scenarios. While this may suggest limited conceptual understanding, analysis of reasons provided by participants suggested that errors often stemmed from misapplied heuristics. For example, cohesion was sometimes overlooked, leading to incorrect identification of the lowest factor of safety; larger failing masses were sometimes incorrectly associated with lower safety in frictional materials; and masses were sometimes incorrectly assumed as driving moments rather than resisting moments when considering the point of rotation. Addressing these misconceptions could significantly enhance practitioner performance.