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Forecasting the long-term deterioration of a cut slope in high-plasticity clay using a numerical model

Lookup NU author(s): Dr Peter Helm, Professor Stephanie Glendinning, Dr Mohamed Rouainia



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


© 2020 The Author(s). This paper details development of a numerical modelling approach that has been employed to forecast the long-term performance of a cut slope formed in high plasticity clay. It links hydrological and mechanical behaviour in a coupled saturated and unsaturated model. This is used to investigate the influence of combined dissipation of excavation-generated excess pore water pressures and seasonal weather-driven near-surface cyclic pore water pressures. Deterioration of slope performance is defined in terms of both slope deformations (i.e. service) and factor of safety against shear failure (i.e. safety). Uniquely, the modelling approach has been validated using 16 years of measured pore water pressure data from multiple locations in a London Clay cut slope. Slope deterioration was shown to be a function of both construction-induced pore water pressure dissipation and seasonal weather-driven pore water pressure cycles. These lead to both transient and permanent changes in factor of safety due to effective stress variation and mobilisation of post-peak strength reduction over time, respectively, ultimately causing shallow first-time progressive failure. It is demonstrated that this long-term (90 year) deterioration in slope performance is governed by the hydrological processes in the weathered near surface soil zone that forms following slope excavation.

Publication metadata

Author(s): Postill H, Helm PR, Dixon N, Glendinning S, Smethurst JA, Rouainia M, Briggs KM, El-Hamalawi A, Blake AP

Publication type: Article

Publication status: Published

Journal: Engineering Geology

Year: 2020

Volume: 280

Print publication date: 01/01/2021

Online publication date: 16/11/2020

Acceptance date: 05/11/2020

Date deposited: 07/01/2021

ISSN (print): 0013-7952

ISSN (electronic): 1872-6917

Publisher: Elsevier B.V.


DOI: 10.1016/j.enggeo.2020.105912


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