Modified Semi-Analytical Method for 3D Slope Reliability

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An improved method for the reliability analysis of 3D slopes has been proposed based on the semi-analytical method of Vanmarcke (1977). Comparing the predicted responses of an idealised 3D slope obtained by the more general, albeit computationally intensive, random finite element method (RFEM), and the original semi-analytical method showed that the latter gives unconservative estimates of the probability of failure. Three significant areas were identified as requiring improvement in the simpler method. These were corrected by: (i) a correction factor to reduce the overestimation of endresistance in 3D failures, i.e. reducing the impact of conservative geometric assumptions; (ii) a correction factor to correct for overestimating the average shear strength on the failure plane, which is found to be lower than the average shear strength for the entire slope; and (iii) an alternative relationship for the expected failure length for intermediate values of the spatial correlation length of the shear strength. The proposed modified semi-analytical method gives substantially improved results that are comparable to RFEM, while retaining the simplicity of the original method.
Original languageEnglish
Title of host publicationProceedings of the 7th International Symposium on Geotechnical Safety and Risk (ISGSR 2019)
Subtitle of host publicationState-of-the-Practice in Geotechnical Safety and Risk
EditorsJianye Ching, Dian-Qing Li, Jie Zhang
Place of PublicationTaipei, Taiwan
Number of pages6
ISBN (Electronic)978-981-11-2725-0
Publication statusPublished - 2019
EventISGSR 2019: 7th International Symposium on Geotechnical Safety and Risk - National Taiwan University of Science and Technology, Taipei, Taiwan
Duration: 11 Dec 201913 Dec 2019


ConferenceISGSR 2019: 7th International Symposium on Geotechnical Safety and Risk
Abbreviated titleISGSR 2019
Internet address

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • Analytical
  • finite element analysis
  • random fields
  • slope stability
  • spatial variability
  • three dimensional


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