The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
A S Obrien - One of the best experts on this subject based on the ideXlab platform.
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the influence of tree root water uptake on the long term hydrology of a Clay Fill railway embankment
Transportation geotechnics, 2016Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a Clay Fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. When all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.
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the use of laboratory testing in the characterisation of embankment Clay Fill from the uk rail network
2015Co-Authors: G Taylor, J Smethurst, A S Obrien, R Tan, Geoff Watson, J S Lane, E EvansAbstract:Most railway embankments in the UK were built in the Victorian era and are of end-tipped construction using materials (usually cohesive) excavated from adjacent cuttings, resulting in a clod-and-matrix structure. Historically there has been a lack in understanding of the mechanical behaviour of such railway embankments. In the next decade railway traffic in the UK, particularly freight, is forecast to grow considerably. Consequently there is a need to improve the understanding of how increases in rail traffic loading may influence the mechanical behaviour of railway embankments and thus track performance. The Rail Safety Standards Board in conjunction with Network Rail is currently undertaking a programme of applied research into this topic. As part of these studies a programme of laboratory element tests has been carried out on samples of embankment Clay Fill; the stress-strain characteristics of the embankment Clay Fill, particularly its non-linear characteristics at small strain, are important factors governing railway embankment deformation. The main objective of the element testing was to measure the accumulation of irrecoverable plastic strain in the Clay Fill specimens and thus aid the understanding of railway embankment behaviour when subject to repeated traffic loading. Samples of intact material were recovered from an existing railway embankment; samples were also recovered from a model test embankment constructed as part of a complementary programme of physical model testing. The embankment Clay Fill sampled was of a medium to high plasticity, representative of embankments on the UK railway network. This paper summarises the laboratory element test programme and the conclusions drawn.
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wet winter pore pressures in railway embankments
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2013Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper demonstrates the influence of extreme wet winter weather on pore water pressures within Clay Fill railway embankments, using field monitoring data and numerical modelling. Piezometer readings taken across the London Underground Ltd network following the wet winter of 2000/2001 were examined, and showed occurrences of hydrostatic pore water pressure within embankments but also many readings below this. A correlation was found between the maximum pore water pressures and the permeability of the embankment foundation soil, with high permeability foundation soils (of Chalk or river terrace deposits) providing underdrainage and maintaining low pore water pressures within the overlying Clay embankment Fill. Numerical modelling of transient water flow in response to a climate boundary condition supports this conclusion and has been used to demonstrate the influence of Clay Fill and underlying foundation permeability on transient pore water pressures during extreme (c. 1 in 100 year) and intermediate (c. 1 in 10 year) wet winter rainfall. For Clay founded embankments, extreme wet winter conditions increased pore water pressures significantly compared with an intermediate winter, while for embankments underlain by a permeable stratum pore water pressures were less sensitive to the extreme winter rainfall.
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old railway embankment Clay Fill laboratory experiments numerical modelling and field behaviour
ADVANCES IN GEOTECHNICAL ENGINEERING - THE SKEMPTON CONFERENCE. A THREE DAY CONFERENCE ON ADVANCES IN ENGINEERING ORGANISED BY THE INSTITUTION OF CIVI, 2004Co-Authors: R J Jardine, A S Obrien, D M Potts, K G Higgins, E A Ellis, D RussellAbstract:UK railway embankments are typically more than 100 years old, and, in southern England, are generally composed of high plasticity Clay Fills. They were built without compaction by end-tipping loosely into place. Significant vegetation growth has developed and, depending on the vegetation type and extent, the embankments are prone to collapse or to severe serviceability problems. The paper summarises laboratory test results on block samples of Clay Fill. Tests were also carried out on reconstituted soils. The paper considers the varying influences of 'structure' on strength, stiffness and permeability characteristics. Numerical analyses were carried out which utilised a non-linear stress-strain model, both pre-peak and post-peak with strain softening towards residual strength. A challenging area is understanding the influence of vegetation; the behaviour of trees compared with grass is considered. The numerical model predictions are compared with a case history where seasonal variations in track displacement were monitored. For the covering abstract see ITRDE128041.
Kevin Briggs - One of the best experts on this subject based on the ideXlab platform.
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macropore structure and permeability of Clay Fill samples from a historic Clay Fill earthwork
Transportation geotechnics, 2019Co-Authors: D Muddle, Kevin BriggsAbstract:Abstract Near surface macropores and macro features (e.g. cracks and fissures) provide pathways for rapid water infiltration into the core of Clay Fill earthworks. However it is more difficult to measure the size and distribution of macropores located below the weathered soil surface (>1.5 m depth) and hence assess their influence on water flow through the Clay Fill core of an earthwork. This paper explores the influence of macropores on the rate of water flow within the core of a historic railway earthwork. Samples were excavated from the core (1.5 m–6.5 m depth) of a Clay Fill railway embankment and subjected to laboratory saturated hydraulic conductivity testing. The samples were scanned using X -ray computed tomography (XCT) before and after laboratory testing. XCT was used to measure the size and distribution of macropores (>63 × 10−6 m) within the samples and compare with the saturated hydraulic conductivity measurements. The results showed that the distribution of macropores and the saturated hydraulic conductivity of the samples from the embankment core was not dependant on the depth of excavation. The total macroporosity of the samples was very small relative to the total porosity (less than 10%). The saturated hydraulic conductivity of the samples was more closely related to the connectivity of the macropores (mean length) than to the total porosity or the total macroporosity. The macropores were variably distributed within the core of the Clay Fill embankment, they did not show a clear relationship with depth and they were connected over relatively short lengths (the mean macropore length was not greater than 1.6 × 10−3 m). Therefore water flow through the core of the embankment is likely to be through the Clay Fill matrix, rather than through the connected macropore pathways which allow rapid water infiltration at the near soil surface (
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Failures in transport infrastructure embankments
Engineering Geology, 2017Co-Authors: Kevin Briggs, Fleur Loveridge, Stephanie GlendinningAbstract:To ensure that road and rail transport networks remain operational, both highway and railway embankments require continual maintenance and renewal to mitigate against ongoing deterioration and repair any sections damaged by realised failures. This paper provides a review of recent developments in the understanding of highway and railway embankment degradation and failure. Failures due to pore water pressure increase, seasonal shrink-swell deformation and progressive failure are considered. The material composition and construction of highway and railway embankments differ, which influences the dominant type and timing of embankment failure. There is evidence for highway embankment failures induced by pore water pressure increase, but not seasonal deformation and progressive failure. Some railway embankments are susceptible to pore water pressure increase, seasonal shrink-swell deformation and progressive failure due to the age and nature of the dumped Clay Fill used in their construction. The approaches used to measure and explore embankment failure mechanisms are compared and discussed. Field observations have been used to understand pore water pressure increase and seasonal shrink-swell deformation in embankments, while the investigation of progressive embankment failure has mainly utilised physical and numerical modelling approaches. Further field and laboratory investigation is required before the rigorous analysis of embankment failure can be routinely undertaken. However, progress is being made to empirically identify and evaluate the various risk factors affecting transport infrastructure embankment failure.
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the influence of tree root water uptake on the long term hydrology of a Clay Fill railway embankment
Transportation geotechnics, 2016Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a Clay Fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. When all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.
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mechanical and hydrological impacts of tree removal on a Clay Fill railway embankment
Geotechnique, 2015Co-Authors: J Smethurst, Kevin Briggs, W Powrie, A Ridley, Derek ButcherAbstract:Seasonal shrinkage and swelling of Clay Fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated Clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the Clay Fill at the crest of the earthwork, but also resulted in the los...
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wet winter pore pressures in railway embankments
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2013Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper demonstrates the influence of extreme wet winter weather on pore water pressures within Clay Fill railway embankments, using field monitoring data and numerical modelling. Piezometer readings taken across the London Underground Ltd network following the wet winter of 2000/2001 were examined, and showed occurrences of hydrostatic pore water pressure within embankments but also many readings below this. A correlation was found between the maximum pore water pressures and the permeability of the embankment foundation soil, with high permeability foundation soils (of Chalk or river terrace deposits) providing underdrainage and maintaining low pore water pressures within the overlying Clay embankment Fill. Numerical modelling of transient water flow in response to a climate boundary condition supports this conclusion and has been used to demonstrate the influence of Clay Fill and underlying foundation permeability on transient pore water pressures during extreme (c. 1 in 100 year) and intermediate (c. 1 in 10 year) wet winter rainfall. For Clay founded embankments, extreme wet winter conditions increased pore water pressures significantly compared with an intermediate winter, while for embankments underlain by a permeable stratum pore water pressures were less sensitive to the extreme winter rainfall.
J Smethurst - One of the best experts on this subject based on the ideXlab platform.
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the influence of tree root water uptake on the long term hydrology of a Clay Fill railway embankment
Transportation geotechnics, 2016Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a Clay Fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. When all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.
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mechanical and hydrological impacts of tree removal on a Clay Fill railway embankment
Geotechnique, 2015Co-Authors: J Smethurst, Kevin Briggs, W Powrie, A Ridley, Derek ButcherAbstract:Seasonal shrinkage and swelling of Clay Fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated Clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the Clay Fill at the crest of the earthwork, but also resulted in the los...
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the use of laboratory testing in the characterisation of embankment Clay Fill from the uk rail network
2015Co-Authors: G Taylor, J Smethurst, A S Obrien, R Tan, Geoff Watson, J S Lane, E EvansAbstract:Most railway embankments in the UK were built in the Victorian era and are of end-tipped construction using materials (usually cohesive) excavated from adjacent cuttings, resulting in a clod-and-matrix structure. Historically there has been a lack in understanding of the mechanical behaviour of such railway embankments. In the next decade railway traffic in the UK, particularly freight, is forecast to grow considerably. Consequently there is a need to improve the understanding of how increases in rail traffic loading may influence the mechanical behaviour of railway embankments and thus track performance. The Rail Safety Standards Board in conjunction with Network Rail is currently undertaking a programme of applied research into this topic. As part of these studies a programme of laboratory element tests has been carried out on samples of embankment Clay Fill; the stress-strain characteristics of the embankment Clay Fill, particularly its non-linear characteristics at small strain, are important factors governing railway embankment deformation. The main objective of the element testing was to measure the accumulation of irrecoverable plastic strain in the Clay Fill specimens and thus aid the understanding of railway embankment behaviour when subject to repeated traffic loading. Samples of intact material were recovered from an existing railway embankment; samples were also recovered from a model test embankment constructed as part of a complementary programme of physical model testing. The embankment Clay Fill sampled was of a medium to high plasticity, representative of embankments on the UK railway network. This paper summarises the laboratory element test programme and the conclusions drawn.
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wet winter pore pressures in railway embankments
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2013Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper demonstrates the influence of extreme wet winter weather on pore water pressures within Clay Fill railway embankments, using field monitoring data and numerical modelling. Piezometer readings taken across the London Underground Ltd network following the wet winter of 2000/2001 were examined, and showed occurrences of hydrostatic pore water pressure within embankments but also many readings below this. A correlation was found between the maximum pore water pressures and the permeability of the embankment foundation soil, with high permeability foundation soils (of Chalk or river terrace deposits) providing underdrainage and maintaining low pore water pressures within the overlying Clay embankment Fill. Numerical modelling of transient water flow in response to a climate boundary condition supports this conclusion and has been used to demonstrate the influence of Clay Fill and underlying foundation permeability on transient pore water pressures during extreme (c. 1 in 100 year) and intermediate (c. 1 in 10 year) wet winter rainfall. For Clay founded embankments, extreme wet winter conditions increased pore water pressures significantly compared with an intermediate winter, while for embankments underlain by a permeable stratum pore water pressures were less sensitive to the extreme winter rainfall.
W Powrie - One of the best experts on this subject based on the ideXlab platform.
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the influence of tree root water uptake on the long term hydrology of a Clay Fill railway embankment
Transportation geotechnics, 2016Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a Clay Fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. When all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.
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mechanical and hydrological impacts of tree removal on a Clay Fill railway embankment
Geotechnique, 2015Co-Authors: J Smethurst, Kevin Briggs, W Powrie, A Ridley, Derek ButcherAbstract:Seasonal shrinkage and swelling of Clay Fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated Clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the Clay Fill at the crest of the earthwork, but also resulted in the los...
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wet winter pore pressures in railway embankments
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2013Co-Authors: Kevin Briggs, J Smethurst, W Powrie, A S ObrienAbstract:This paper demonstrates the influence of extreme wet winter weather on pore water pressures within Clay Fill railway embankments, using field monitoring data and numerical modelling. Piezometer readings taken across the London Underground Ltd network following the wet winter of 2000/2001 were examined, and showed occurrences of hydrostatic pore water pressure within embankments but also many readings below this. A correlation was found between the maximum pore water pressures and the permeability of the embankment foundation soil, with high permeability foundation soils (of Chalk or river terrace deposits) providing underdrainage and maintaining low pore water pressures within the overlying Clay embankment Fill. Numerical modelling of transient water flow in response to a climate boundary condition supports this conclusion and has been used to demonstrate the influence of Clay Fill and underlying foundation permeability on transient pore water pressures during extreme (c. 1 in 100 year) and intermediate (c. 1 in 10 year) wet winter rainfall. For Clay founded embankments, extreme wet winter conditions increased pore water pressures significantly compared with an intermediate winter, while for embankments underlain by a permeable stratum pore water pressures were less sensitive to the extreme winter rainfall.
Derek Butcher - One of the best experts on this subject based on the ideXlab platform.
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mechanical and hydrological impacts of tree removal on a Clay Fill railway embankment
Geotechnique, 2015Co-Authors: J Smethurst, Kevin Briggs, W Powrie, A Ridley, Derek ButcherAbstract:Seasonal shrinkage and swelling of Clay Fill railway embankments can disturb the track geometry, resulting in train speed restrictions that disrupt normal operations. Such movements are exacerbated by vegetation, but reliable analytical descriptions of the effects of trees on embankment behaviour are not yet established. This paper presents and analyses the results of a field experiment, carried out on a heavily vegetated Clay railway embankment to investigate quantitatively the influence of trees. After the first year of monitoring, the mature trees initially present on the upper two-thirds of the embankment slopes were removed. The field monitoring data are used to assess and understand the mechanisms of soil water content and pore water pressure changes before and after tree removal, and their influence on the vertical and lateral displacements of the embankment slopes. Removal of the vegetation stopped seasonal volume changes in the Clay Fill at the crest of the earthwork, but also resulted in the los...