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Strength parameter selection framework for evaluating the design life of clay cut slopes

Lookup NU author(s): Dr Harry Postill, Dr Peter HelmORCiD, Professor Stephanie Glendinning



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Design of engineered earthworks is predominantly conducted through limit equilibrium analysis requiring strain independent strength criteria. Previous studies for deep-seated first-time failures within over-consolidated clay cut slopes have proposed the use of fully softened strength parameters for design. A study investigating shallow first-time failures in clay cut slopes due to seasonal stress cycles has been undertaken using a validated numerical model capable of capturing seasonal ratcheting and progressive failure. It is shown that fully softened strength criteria are inappropriate for the assessment of shallow first-time failures due to seasonal ratcheting and that slopes at angles between the material's fully softened and residual friction angle may be at risk of failure in the future due to this behaviour. However, adopting residual strength parameters will likely result in overly conservative solutions considering the required design life of geotechnical assets. It is shown that the strain-softening behaviour of clay defines the rate of strength deterioration and the operational life of engineered slopes. While general guidelines for analysis considering shallow first-time failures in clay cut slopes are made, detailed understanding of a material's strain-softening behaviour, the magnitude and rate of strength reduction with strains, is needed to establish strength criteria for limit equilibrium analysis.

Publication metadata

Author(s): Postill H, Helm PR, Dixon N, El-Hamalawi A, Glendinning S, Take WA

Publication type: Article

Publication status: Published

Journal: Proceedings of the Institution of Civil Engineers - Geotechnical Engineering

Year: 2021

Issue: ePub ahead of Print

Online publication date: 04/10/2021

Acceptance date: 17/09/2020

Date deposited: 08/11/2021

ISSN (print): 1353-2618

ISSN (electronic): 1751-8563

Publisher: ICE Publishing


DOI: 10.1680/jgeen.21.00125


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