Selecting Minimum Factors of Safety for 3D Slope Stability Analyses

T. D. Stark, D. G. Ruffing

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Geotechnical engineers understand there is uncertainty and risk in the input parameters for slope stability analyses and within the analysis methodologies themselves. Decades of research and inverse analyses of slope failures have resulted in widespread acceptance of certain factors of safety (FS) in typical situations, e.g., a static two-dimensional (2D) factor of safety of 1.3 is often used for temporary or low risk slopes and 1.5 for permanent slopes. However, these FSs are not appropriate for use with three-dimensional (3D) analyses because 3D analyses account for additional shear resistance that is generated along the sides of the slide mass. The contribution of the additional shear resistance can be significant in shallow slide masses or for translational slide masses with a width to height ratio less than six, resulting in calculated values of 3D FS that are greater than the calculated 2D FS. To achieve the same level of safety or risk as a static 2D FS of 1.3 or 1.5, the user must use a greater minimum FS for 3D analyses. This paper presents methods for calculating a suitable minimum 3D FS to achieve a similar level of safety or risk as a minimum 2D FS, such as 1.3 or 1.5, would afford.

Original languageEnglish (US)
Title of host publicationGeotechnical Special Publication
EditorsJinsong Huang, Gordon A. Fenton, Limin Zhang, D. V. Griffiths
PublisherAmerican Society of Civil Engineers
Number of pages8
EditionGSP 283
ISBN (Electronic)9780784480700
StatePublished - 2017
EventGeo-Risk 2017: Reliability-Based Design and Code Developments - Denver, United States
Duration: Jun 4 2017Jun 7 2017

Publication series

NameGeotechnical Special Publication
NumberGSP 283
ISSN (Print)0895-0563


OtherGeo-Risk 2017: Reliability-Based Design and Code Developments
Country/TerritoryUnited States

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Architecture
  • Building and Construction
  • Geotechnical Engineering and Engineering Geology

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