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

Lookup NU author(s): Dr Ross Stirling, Dr Paul Hughes, David Hughes, Professor Stephanie Glendinning

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by The Geological Society of London, 2019.

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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 0.3 and 1.2 metres depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. 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.


Publication metadata

Author(s): Dixon N, Crosby CJ, Stirling R, Hughes PN, Smethurst J, Briggs K, Hughes D, Gunn D, Hobbs P, Loveridge F, Glendinning S, Dijkstra T, Hudson A

Publication type: Article

Publication status: Published

Journal: Quarterly Journal of Engineering Geology and Hydrogeology

Year: 2019

Volume: 52

Issue: 1

Pages: 123-135

Print publication date: 01/02/2019

Online publication date: 16/10/2018

Acceptance date: 01/08/2018

Date deposited: 09/10/2018

ISSN (print): 1470-9236

ISSN (electronic): 2041-4803

Publisher: The Geological Society of London

URL: https://doi.org/10.1144/qjegh2017-059

DOI: 10.1144/qjegh2017-059


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