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| Titel |
Modelling the effect of rock fragment on soil saturated hydraulic conductivity |
| VerfasserIn |
Sergio Pellegrini, Maria Costanza Andrenelli, Nadia Vignozzi |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092520
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| Publikation (Nr.) |
 EGU/EGU2014-6872.pdf |
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| Zusammenfassung |
| Stoniness may be a key factor in determining the soil hydrological properties. Nevertheless,
how coarse fraction takes part in some important processes (e.g., runoff, infiltration and
percolation) is not univocally recognized, mainly because of the difficulties in obtaining
reliable experimental data and, secondarily, for the employment of different approaches to
evaluate the role of the coarse fraction.
With that regard, equations developed by hydrogeologists to account for water fluxes in
porous media, consider permeability as mere function of grain size distribution (particles >2
mm included), with permeability values increasing when passing from sand to gravel.
Conversely, soil scientists consider the saturated hydraulic conductivity (Ksat) of soil
exclusively as function of the fine-earth fraction and attribute a contrasting effect to the
coarse fraction, both in relation to the decrease of porosity and to the increase of flow path
tortuosity. Nevertheless, the Soil Survey Handbook includes all fragmental soils (gravel
content ≥35% by weight) into the highest class of soil hydraulic conductivity, and this partly
disagrees with the mostly adopted soil scientists’ approaches. At the same time, lab-
experiments carried out by engineers on particle mixture point out that the addition of
increasing amounts of coarse material to finer grains progressively reduces the overall
porosity until a critical threshold is reached; beyond this level, the void proportion rises
again.
In relation to the engineers’ results, the present paper attempts to conceptually approach
the dual effects of rock fragment content on Ksat by considering a decay of the water
transmission properties of the fine-earth fraction at low gravel contents and, conversely, a
drastic improvement of the conductivity whenever the porosity increases. For that purpose a
data set of 50 soils of different textural classes is used to define the procedure by
virtually increasing the rock fragment fraction (SK) up to 99% by weight, meanwhile
calculating the corresponding statistical descriptors (e.g., d10, dg, ÏăÏ) of grain size
distribution (GSD). For each sample of the data set, the procedure is based on the Ksat
computation for increasing gravel content provided by both soil scientists’ and
hydrogeologists’ approaches. Given that the two methods generate curves with
different direction and slope, an intersection is obtained. Such a point indicates the
minimum saturated hydraulic conductivity value, that can be conceptually interpreted as
the minimum porosity (or the maximum density of the mixture) experimentally
observed by engineers. Therefore, the procedure for assessing the resulting Ksat
consists in adopting the soil scientists’ approach until the intersection is reached
and then following the hydrogeological curve beyond such threshold. The findings
provided by two other approaches are compared with our results and discussed. |
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