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Centrifuge and numerical modelling of triggers of slope failures
Thesis (PhD (Civil Engineering))--University of Pretoria, 2025.
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University of Pretoria
2025
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| _version_ | 1867613486211661824 |
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| access_status_str | Open Access |
| author2 | Jacobsz, Schalk Willem |
| author_browse | Jacobsz, Schalk Willem |
| author_facet | Jacobsz, Schalk Willem |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD (Civil Engineering))--University of Pretoria, 2025. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/104975 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:36:54.588Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/104975 Centrifuge and numerical modelling of triggers of slope failures Jacobsz, Schalk Willem arnocrous2313@gmail.com Crous, Petrus Arnoldus UCTD Sustainable Development Goals (SDGs) Slope stability Tailings Finite element method Trigger Centrifuge modelling Thesis (PhD (Civil Engineering))--University of Pretoria, 2025. This research investigates the triggers and mechanisms of slope failures in fine sand, focusing on both drained instability and triggers of undrained instability. It addresses a critical issue in geotechnical engineering: ensuring the stability of slopes constructed with brittle soils, such as tailings dams and loose fill slopes under varying loading and environmental conditions. Historically, slope stability assessments have relied on drained shear strength. However, the introduction of new international standards in response to recent failures have underscored the need to consider undrained conditions and their role in triggering slope failures. The 2019 Brumadinho tailings dam disaster highlighted the uncertainty surrounding failure mechanisms, as different expert panels proposed differing triggers.This study investigated a range of triggers that might result in the triggering of undrained slope instability through physical modelling in the geotechnical centrifuge, complemented by limit equilibrium (LE) and finite element method (FEM) numerical analysis. The triggers investigated included drained instability resulting from a rising water table, rapid removal of confinement at the toe of the slope, rapid buttress construction against the toe, rapid surcharge loading at the crest of the slope and fluid injection into a hydraulically continuous layer associated with borehole drilling. The tests also examined the effects of soil density, pore fluid viscosity and soil saturation state on failure mechanisms.In this study, slope failure typically occurred when the drained factor of safety approached unity. A dense slope subjected to a rising water table exhibited progressive sloughing, gradually propagating upwards along the slope, never resulting in catastrophic failure. Loose slopes experienced rapid, deep seated, brittle failures, initiating from drained instability, transitioning to undrained shearing due to the rapidity of collapse. Rapid removal of confinement at the toe resulted in similar responses to those observed during drained instability, suggesting that the two instability mechanisms (i.e. drained instability and loss of confinement) resulted in practically indistinguishable pore pressure and deformation responses upon failure. The importance of toe stability and saturation was evident. Slopes with unsaturated toes remained stable under imposed triggers, whereas near full saturation of the toe was a precursor to failure. It was found that even slight disturbance of a near-saturated toe, such as the construction of a buttress, triggered slope failure. Surcharge loading at the crest led to negligible excess pore pressures due to stress redistribution in unsaturated soil overlying the water table and triggered drained instability after a slight pause. Finally, raising pore pressures in a hydraulically continuous layer, simulating conditions during drilling with water, was shown to be a credible trigger of undrained instability due to localised loss of effective stress and hence strength.Instances where positive pore pressures were observed during failure, presumed to be indicative of undrained conditions, were highly localised to some regions within the saturated sand, with the most susceptible region being the saturated toe. Despite the model slopes being prepared in as loose a state as possible, negative pore pressure measurements were far more commonly observed upon failure than positive responses, suggesting that modelling all materials below the water table as undrained is a very conservative approach.Numerical back-analyses were conducted using the LE method and the FEM with the NorSand constitutive model. LE analyses indicated that slope failures were triggered when the drained factor of safety was approximately one. In this study, slope failure could not be triggered by the trigger mechanisms modelled, unless the drained factor of safety was one. The NorSand FEM models captured pre-failure mechanisms, such as pore pressure responses and stress path development. Additionally, the NorSand FEM models were capable of capturing deep-seated failures as observed in the centrifuge models. It is recommended to analyse the stability of slopes using the drained strength in combination with the appropriate pore pressures to cater for partially drained or undrained conditions. The results of this study suggest that modelling all material below the water table as undrained is an over-conservative approach. Recommendations are provided for improving slope stability assessment, design and management of tailings and other man-made slopes. Future work should focus on refining numerical models to better capture post-failure mechanisms. Anglo American Civil Engineering PhD (Civil Engineering) Unrestricted Faculty of Engineering, Built Environment and Information Technology None 2025-10-24T08:37:32Z 2025-10-24T08:37:32Z 2026-04 2025-07 Thesis * A2026 http://hdl.handle.net/2263/104975 https://doi.org/10.25403/UPresearchdata.30437035.v1 N/A en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Slope stability Tailings Finite element method Trigger Centrifuge modelling Centrifuge and numerical modelling of triggers of slope failures |
| title | Centrifuge and numerical modelling of triggers of slope failures |
| title_full | Centrifuge and numerical modelling of triggers of slope failures |
| title_fullStr | Centrifuge and numerical modelling of triggers of slope failures |
| title_full_unstemmed | Centrifuge and numerical modelling of triggers of slope failures |
| title_short | Centrifuge and numerical modelling of triggers of slope failures |
| title_sort | centrifuge and numerical modelling of triggers of slope failures |
| topic | UCTD Sustainable Development Goals (SDGs) Slope stability Tailings Finite element method Trigger Centrifuge modelling |
| url | http://hdl.handle.net/2263/104975 https://doi.org/10.25403/UPresearchdata.30437035.v1 |