BE-02 Open cut method Lesson: Utility Trench Construction

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Geotechnology
Geotechnology (2)
Subsoil - Geomechanical Principles
Geomechanical Principles
Hydrogeological Basics
End of Lesson

Soil Permeability

How to Determine the Soil Permeability Coefficient? (2)

Prior to the design and dimensioning of technical details, investigations according to [ASTM D2434] and/or [DIN18130-1:1998] should also be included. Their evaluation is based on the application of Darcy‘s law and, as a result, provides the permeability coefficient k.

k = \frac{v}{I}

Formula:

permeability coefficient k according to Darcy‘s law

v Filter velocity in the soil sample [m/s]

I Applied hydraulic gradient [-]

[ASTM D2434]

American Society for Testing and Materials (2006). ASTM Standard D422 Standard Test Method for Permeability of Granular Soils (Constant Head) (Withdrawn 2015). ASTM International, West Conshohocken, PA. www.astm.org

DIN18130-1:1998

DIN 18130-1: Baugrund; Versuche und Versuchsgeräte; Kalkgehaltsbestimmung; Bestimmung des Wasserdurchlässigkeitsbeiwertes Laborversuche (11.1989).
[Soil - Experiments and experimental equipment; lime content; Determination of the water permeability coefficient Laboratory tests]
Das Dokument wurde zurückgezogen. Das gültige Ersatzdokument ist: Document was withdrawn and substituted by:
DIN18130-1: Baugrund - Untersuchung von Bodenproben; Bestimmung des Wasserdurchlässigkeitsbeiwerts - Teil 1: Laborversuche (05.1998).
[Soil - investigation of soil samples; Determination of water permeability coefficient - Part 1: Laboratory experiments]

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Darcy‘s law states that the water quantity Q, that laminarily traverses an area A in a porous medium (e.g. sand), is directly proportional to the hydraulic gradient i. The proportionality factor of this relation, i.e. the k-value (permeability coefficient), is a characteristic parameter for the porous medium and the traversing fluid (liquid or gas).

This interrelation represents the fundamental law of the linear, unidimensional water flow in incohesive types of soil as a result of gravitational forces. Darcy‘s flow law has been proven to be true for many types of soil and soil conditions. However, subject to the given particle diameters and the hydraulic gradient, it might reach the limits of the linear region in extreme cases.

In such cases, the permeability coefficient k loses its constant character and represents a parameter that is directly dependent on the existing hydraulic gradient. Thus, Darcy‘s law cannot be applied for coarse rubble and coarse gravel, for example (see next slide) [Kolym98].