Permeability Testing in Unconsolidated Materials
by: Sebastien Fortin, E.I.T., M.Sc.
Field Methods for the Vadose Zone
For field methods in the vadose zone, a distinction must be made between "saturated" (Ks) and "field-saturated" (Kfs) hydraulic conductivity. True saturated conditions seldom occur in the vadose zone except where impermeable layers result in the presence of perched water tables. During infiltration events or in the event of a leak from a lined pond, a "field-saturated" condition develops. True saturation does not occur due to entrapped air. The entrapped air prevents water from moving in air-filled pores that, in turn, may reduce the hydraulic conductivity measured in the field by as much as a factor of two compared to conditions when trapped air is not present (i.e. full saturation). Field tests methods in the vadose zone generally simulate the "field-saturated" condition. The hydraulic conductivity measured in the unsaturated (vadose) zone is thus referred to as the "field-saturated" hydraulic conductivity (Kfs) (Reynolds et al, 1983).
Several test methods are available for determining the field saturated hydraulic conductivity (Kfs) of unsaturated materials above the water table. Most of the methods involve measurement of the infiltration rate of water into the soil or mine waste from an infiltrometer or permeameter device. Infiltrometers typically measure hydraulic conductivity at the soil surface, whereas permeameters may be used to determine hydraulic conductivity at different depths within the soil profile.
In general, field methods for testing permeability in the vadose zone can be subdivided into the following categories:
Borehole Permeameter Tests;
Infiltration Tests;
Other Methods.
Field tests used for determining the value of Kfs can either be constant head tests and falling head tests. Most field methods that do not use piezometers correspond to constant head tests. These various methods are briefly presented in the following paragraphs. The interested reader is encouraged to consult the list of references provided in the sections below, which summarizes the principle, operation mode and interpretation of each of these field methods. Table 1 compares different field test methods commonly used for measuring hydraulic conductivity in the vadose zone of soils.
The remainder of this paper describes the various field methods for determining field-saturated permeability in the unsaturated (vadose) zone.
Forward to Borehole Permeameter Tests.
Return to Methods of Permeability Testing.
|
|
/ Surface Water
