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In situ measurements of near-surface hydraulic conductivity in engineered clay slopes

In situ measurements of near-surface hydraulic conductivity in engineered clay slopes
In situ measurements of near-surface hydraulic conductivity in engineered clay slopes
In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved due to preferential and by-pass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0 to 0.3 metres depth), decreasing by four orders of magnitude between 0 and 1.2 metres depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content (up to 1.5 orders of magnitude). Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependency of a two orders of magnitude decrease from 0.2 to 0.6 metres depth. The main factor controlling the large range is found to be spatial variability in the soil macro structure generated by wetting/drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather/vegetation/infiltration/soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.
1470-9236
123-135
Dixon, Neil
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Crosby, Chris J
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Stirling, Ross
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Hughes, Paul N
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Smethurst, Joel
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Briggs, Kevin
8974f7ce-2757-4481-9dbc-07510b416de4
Hughes, David
d3b52ac5-5b40-4694-8350-927e4c292ecb
Gunn, David
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Hobbs, Peter
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Loveridge, Fleur
fb5b7ad9-d1b8-40d3-894b-bccedf0e8a77
Glendinning, Stephanie
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Dijkstra, Tom
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Hudson, Andrew P
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Dixon, Neil
6272601b-f201-4828-898b-2b4b8d5e08c0
Crosby, Chris J
3860314d-1844-4c5f-b433-f032201a4c64
Stirling, Ross
db08b140-8662-4c14-b889-0cf6a7d6c56d
Hughes, Paul N
6eb480ef-5702-4fbd-b022-7cd098c5c7be
Smethurst, Joel
8f30880b-af07-4cc5-a0fe-a73f3dc30ab5
Briggs, Kevin
8974f7ce-2757-4481-9dbc-07510b416de4
Hughes, David
d3b52ac5-5b40-4694-8350-927e4c292ecb
Gunn, David
e8d344cd-c386-4514-af02-c4570c968d13
Hobbs, Peter
4051c5c2-b4de-466b-a181-fde7bbf7ee9c
Loveridge, Fleur
fb5b7ad9-d1b8-40d3-894b-bccedf0e8a77
Glendinning, Stephanie
c0be9556-3210-4794-a36b-a483258a4b45
Dijkstra, Tom
32bcc951-6d68-4317-8c83-8335e45e67be
Hudson, Andrew P
c834356f-d618-49d2-a8cc-cd338e1a87a4

Dixon, Neil, Crosby, Chris J, Stirling, Ross, Hughes, Paul N, Smethurst, Joel, Briggs, Kevin, Hughes, David, Gunn, David, Hobbs, Peter, Loveridge, Fleur, Glendinning, Stephanie, Dijkstra, Tom and Hudson, Andrew P (2019) In situ measurements of near-surface hydraulic conductivity in engineered clay slopes. Quarterly Journal of Engineering Geology and Hydrogeology, 52 (1), 123-135. (doi:10.1144/qjegh2017-059).

Record type: Article

Abstract

In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved due to preferential and by-pass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0 to 0.3 metres depth), decreasing by four orders of magnitude between 0 and 1.2 metres depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content (up to 1.5 orders of magnitude). Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependency of a two orders of magnitude decrease from 0.2 to 0.6 metres depth. The main factor controlling the large range is found to be spatial variability in the soil macro structure generated by wetting/drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather/vegetation/infiltration/soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.

Text
Dixon et al Hydraulic Conductivity paper QJEGH FINAL 01aug18 - Accepted Manuscript
Restricted to Repository staff only until 1 August 2019.
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Accepted/In Press date: 1 August 2018
e-pub ahead of print date: 31 August 2018
Published date: 5 February 2019

Identifiers

Local EPrints ID: 422718
URI: https://eprints.soton.ac.uk/id/eprint/422718
ISSN: 1470-9236
PURE UUID: 2693d461-73ca-45ef-8a4c-dffa3ad62461

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Date deposited: 01 Aug 2018 16:30
Last modified: 13 Mar 2019 18:12

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Contributors

Author: Neil Dixon
Author: Chris J Crosby
Author: Ross Stirling
Author: Paul N Hughes
Author: Joel Smethurst
Author: Kevin Briggs
Author: David Hughes
Author: David Gunn
Author: Peter Hobbs
Author: Fleur Loveridge
Author: Stephanie Glendinning
Author: Tom Dijkstra
Author: Andrew P Hudson

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