University of Missouri – Columbia
Civil and Environmental Engineering
PERMEABILITY TEST
PURPOSE
The purpose of this laboratory is to teach you how to measure the hydraulic conductivity of soils
using constant and falling head tests. Although field permeability tests are generally to be
preferred over laboratory tests (because field tests include the effects of joints, fissures, root
holes, and other similar defects better than do laboratory tests), laboratory tests are still very
useful for:
 tests on compacted soils

studies of the effects of variables such as chemistry of the permeating fluid
 studies of the effects of direction of fluid flow on hydraulic conductivity
Laboratory tests also have the advantage of being far less expensive than field tests, which is
probably the main reason why laboratory tests are still performed in relatively large numbers.
BACKGROUND
Terminology
Analysis of water flow in soil is usually based on Darcy's (1856) law. The law has been written
in many forms, depending on the discipline of the user and the date of usage. The form most
commonly encountered is:
A
i
k
q
⋅
⋅

=
(1)
where q is the rate of flow (units of L
3
/T), i is the hydraulic gradient (the dimensionless ratio of
rate of change of total head with respect to position along the path of flow), A is the cross
sectional area of flow (L
2
), and k is a constant of proportionality (L/T) that is termed hydraulic
conductivity in most disciplines but is often termed coefficient of permeability, or just
permeability, by many civil engineers.
In addition to being dependent on the properties of the soil, k is also dependent upon the
properties of the permeating fluid. For example, motor oil will flow through a specimen of sand
more slowly than water, all other factors being equal. To take into account the properties of the
fluid, Darcy's law may be written in an alternative form:
A
i
K
q
w
⋅
⋅

=
m
g
(2)
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentUniversity of Missouri – Columbia
Civil and Environmental Engineering
Permeability Test
p.2
where
γ
w
(M/L
2
T
2
) and
μ
(ML/T) are the unit weight and viscosity of the fluid, respectively, and
K is a constant of proportionality (L
2
) that is termed the coefficient of permeability in most
disciplines but is sometimes termed intrinsic permeability.
A third form of Darcy's law is:
A
dx
dp
k
q
⋅

=
m
(3)
where q is the rate of flow in units of cubic centimeters per second,
μ
is the viscosity of the fluid
in units of centipoises, p is the pressure in the fluid in units of atmospheres, x is the position
along the path of flow in units of centimeters, A is the crosssectional area of flow in units of
square centimeters, and k is the permeability in units of "darcies." For a permeant liquid of pure
water at 20°C, the conversions are:
1 cm/sec = 1.02 x 10
5
cm
2
= 1.04 x 10
3
darcy
Because of the simplicity of Eq. 1 and the fact that geotechnical engineers are usually concerned
with flow of a single fluid (water), most geotechnical engineers prefer to use Eq. 1. We will also
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '11
 Rosenblad
 Hydrology, Environmental Engineering, Geotechnical Engineering, Aquifer, Civil and Environmental Engineering, permeability test

Click to edit the document details