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The effect of increased axle loading on saturated and unsaturated railway foundation materials
Thesis (PhD)--University of Pretoria, 2020.
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| Format: | Thesis |
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University of Pretoria
2021
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| _version_ | 1867613609221160960 |
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| access_status_str | Open Access |
| author2 | Grabe, P.J. (Hannes) |
| author_browse | Grabe, P.J. (Hannes) |
| author_facet | Grabe, P.J. (Hannes) |
| collection | Thesis |
| dc_rights_str_mv | © 2019 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)--University of Pretoria, 2020. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/78939 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:38:52.072Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| 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:2263/78939 The effect of increased axle loading on saturated and unsaturated railway foundation materials Grabe, P.J. (Hannes) david.mpye@up.ac.za Mpye, Godisang David UCTD increased axle loading railway foundation materials cyclic loading triaxial testing saturated and unsaturated soils Engineering, built environment and information technology theses SDG-09 SDG-09: Industry, innovation and infrastructure Engineering, built environment and information technology theses SDG-11 SDG-11: Sustainable cities and communities Thesis (PhD)--University of Pretoria, 2020. The aim of the research is to investigate the effect of increased axle loading on saturated and unsaturated railway foundation materials for heavy haul applications. The research methodology comprises of a literature review to identify the lacuna in the scientific knowledge, finite element modelling for characterisation of railway cyclic loading, development of a cyclic triaxial apparatus for laboratory testing and experimental work, followed by analysis, interpretation and discussion of results and lastly the formulation of conclusions and recommendations. The axle loading of interest start with a base load of 20 tonnes per axle for general freight followed by increased axle loading of 26, 30, 32.5 and 40 tonnes per axle for heavy haul. The test materials used in the experimental work are representative of the subballast and subgrade layers in a railway substructure. As a reproduction of the climatic conditions in the field and the loading from passing trains, experimental testing was carried out on saturated samples under undrained conditions and unsaturated samples under constant water content. Unsaturated samples were prepared to matric suctions of 50, 100 and 225 kPa via axis translation. Monotonic and cyclic tests were conducted to investigate the behaviour of railway foundation materials. Critical state theory for saturated and unsaturated soils is used as a method of analysis in establishing the failure criterion and the failure envelope. Various parameters, such as stress states, strains, resilient modulus, pore water pressure and matric suction are also utilised in investigating trends and behaviours. Based on the monotonic test results, the shear strength of unsaturated samples was found to be greater than that of saturated samples, attributed mainly to strain hardening caused by the unsaturated soil conditions, with the presence of a peak deviator stress when plotted on the stress-strain graph. However, unsaturated samples were also found to be prone to load-collapse during monotonic shear, even when the water content and confining stress remained constant, which resulted in brittle behaviour with the sudden rupture and formation of multiple bifurcation shear bands and slip planes. Based on the cyclic tests on saturated materials, it was discovered that increased axle loading can result in phase-transition in soil behaviour, based on the stress states in the soil relative to the critical state line plotted in the effective stress space. Stress states below the critical state line resulted in a no-phase transition with dilation behaviour. Stress states on the critical state line resulted in a single-phase transition from dilation to contraction. Stress states above the critical state line resulted in a double-phase transition from dilation to contraction behaviour and then strain-softening. It is therefore concluded that increased axle loading can only be sustained by materials which presented dilation and no phase-transition in soil behaviour, which occurred at axle loading of 20 and 26 tonnes per axle for the subballast and subgrade materials. Based on the cyclic tests on unsaturated materials, it was established that increased axle loading did not cause material failure for all load axle cases and materials. The stress states of all tests plotted well below the failure envelope in the net stress space, which is indicative of resilient and elastic behaviour. Increased axle loading instead resulted in decreased permanent strain, until the critical level of repeated deviator stress of 32.5 tonnes per axle was found, where the permanent strain increased. It is therefore concluded that, as a result of the increased shear strength from the strain hardening property of unsaturated materials, an increased axle loading of 32.5 tonnes per axle can be safely sustained by the tested materials provided the matric suction in the soil is greater than 50 kPa. Civil Engineering PhD Unrestricted 2021-03-04T09:34:44Z 2021-03-04T09:34:44Z 2021-04-20 2020 Thesis Mpye, GD 2020, The effect of increased axle loading on saturated and unsaturated railway foundation materials, PhD Thesis, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/78939> A2021 http://hdl.handle.net/2263/78939 en © 2019 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 increased axle loading railway foundation materials cyclic loading triaxial testing saturated and unsaturated soils Engineering, built environment and information technology theses SDG-09 SDG-09: Industry, innovation and infrastructure Engineering, built environment and information technology theses SDG-11 SDG-11: Sustainable cities and communities The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title | The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title_full | The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title_fullStr | The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title_full_unstemmed | The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title_short | The effect of increased axle loading on saturated and unsaturated railway foundation materials |
| title_sort | effect of increased axle loading on saturated and unsaturated railway foundation materials |
| topic | UCTD increased axle loading railway foundation materials cyclic loading triaxial testing saturated and unsaturated soils Engineering, built environment and information technology theses SDG-09 SDG-09: Industry, innovation and infrastructure Engineering, built environment and information technology theses SDG-11 SDG-11: Sustainable cities and communities |
| url | http://hdl.handle.net/2263/78939 |