Pneumatic Permeability (Air
|Scope and Use
soil remediation operations
such as: soil-vapor extraction, air sparging, backfilling of soils in
utility trenches, and similar engineering activities. This test
method covers laboratory determination of the Coefficient of
permeability for the flow of air (pneumatic permeability) through
partially saturated porous materials. This test method may be used with
undisturbed or compacted coarse grained soils, silts, or lean cohesive
soils that have a low degree of saturation and that have pneumatic
Permeability between 0.001 square micrometers (1.01milli- darcy) and
100 square micrometers (101darcy).
This test method is based on the assumption
that the rate of air flow through the specimen is constant with
time. When a specimen contains volatile materials this assumption
is violated. The mass of gas flowing out will be greater than
that flowing in, the pneumatic gradient is indeterminate and the test
may become meaningless. Such specimens pose special problems and
must be decontaminated before analysis in order to minimize health and
safety concerns and to prevent contamination of the test apparatus.
The pneumatic permeability of porous materials
may be strongly dependent on a variety of physical properties including
the void ratio, the degree of saturation, percent and direction of
compaction, and so forth. It is beyond the scope of this test
method to elaborate these dependencies. Rather, this test method
is intended to be a measurement technique for determining the pneumatic
permeability under a certain set of laboratory conditions. It is
the responsibility of the requestor to specify which soil parameters
must be controlled to ensure a valid extension of the test results to
For some specimens, the pneumatic permeability
will be strongly dependent on the effective confining stress due to
porosity reduction. Whenever possible, the requestor should
specify the field overburden conditions at which this test method is to
be performed. In some specimens, this stress will vary
significantly with flow in an indeterminate way. Cooper Testing
Labs can perform this test at multiple effective confining stresses if
a porous medium to
conduct gas in the presence of a gas (air) pressure gradient measured
as the ratio of volumetric flow through a specimen to the resultant
pressure drop across it. This is also commonly known as pneumatic
conductivity or air permeability. As a sample becomes more
saturated, the air permeability will decrease because the amount of
air-filled pore spaces available for flow decreases.
Effective permeability - A measure of the
ability of a single fluid to flow through a rock when the pore spaces
of the rock are not completely filled or saturated with that fluid.
Intrinsic permeability - While air
permeability or hydraulic conductivity are a function of both the
porous medium and the fluid flowing through it, the intrinsic
permeability is only a function of the medium itself and is independent
of the permeating fluid. The intrinsic permeability is a function
of the size of the pore spaces through which the fluid moves.
|Undisturbed (can also be run on a remolded
||Brass or steel liner (shelby tube); pitcher
|2", 2.5", 3", 4" and 6”. Two-inch diameter
samples and smaller can be tested but are not recommended due to
typical sampling disturbance seen in these small diameter
samples. See our newsletter article regarding sample diameter and
disturbance for more information. Testing costs for four and six inch
diameter samples are higher than the standard cost. See our fee schedule for more
||The minimum sample height should be greater than 2
to 2.5 times the diameter. More sample is required if other tests
will be performed.
||The sample should be sealed to prevent the loss of
moisture and be kept cool, but not frozen, and in a vertical position.
The sample should be delivered to the lab as soon as practical after
||It is critical to handle with care. The
permeability test can be very sensitive to sample disturbance.
effective permeability (Native State – In-situ moisture content), 5
business days, depending on quantity and workload. For intrinsic
permeability (Specific permeability – air dry state) approximately 10
business days depending on the length of time required to air-dry the
specimen while avoiding cracking.