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

Dixon, N. and Crosby, C.J. and Stirling, R. and Hughes, P.N. and Smethurst, J. and Briggs, K. and Hughes, D. and Gunn, D. and Hobbs, P. and Loveridge, F. and Glendinning, S. and Dijkstra, T. and Hudson, A. (2019) 'In situ measurements of near-surface hydraulic conductivity in engineered clay slopes.', Quarterly journal of engineering geology and hydrogeology., 52 (1). 23-135.


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.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:Dixon, N., Crosby, C.J., Stirling, R., Hughes, P.N., Smethurst, J., Briggs, K., Hughes, D., Gunn, D., Hobbs, P., Loveridge, F., Glendinning, S., Dijkstra, T. & Hudson, A. (2019). In situ measurements of near-surface hydraulic conductivity in engineered clay slopes. Quarterly Journal of Engineering Geology and Hydrogeology 52(1): 123-135 © Geological Society of London 2018.
Date accepted:01 August 2018
Date deposited:12 September 2018
Date of first online publication:31 August 2018
Date first made open access:31 August 2019

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