ASTM D6527-00
(Test Method)Standard Test Method for Determining Unsaturated and Saturated Hydraulic Conductivity in Porous Media by Steady-State Centrifugation
Standard Test Method for Determining Unsaturated and Saturated Hydraulic Conductivity in Porous Media by Steady-State Centrifugation
SCOPE
1.1 This test method covers the determination of the hydraulic conductivity, or the permeability relative to water, of any porous medium in the laboratory, in particular, the hydraulic conductivity for water in subsurface materials, for example, soil, sediment, rock, concrete, and ceramic, either natural or artificial, especially in relatively impermeable materials or materials under highly unsaturated conditions. This test method covers determination of these properties using any form of steady-state centrifugation (SSC) in which fluid can be applied to a specimen with a constant flux or steady flow during centrifugation of the specimen. This test method only measures advective flow on core specimens in the laboratory.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D6527–00
Standard Test Method for
Determining Unsaturated and Saturated Hydraulic
Conductivity in Porous Media by Steady-State
Centrifugation
This standard is issued under the fixed designation D 6527; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 5084 Test Method for Measurement of Hydraulic Con-
ductivity of Saturated Porous Materials Using a Flexible
1.1 This test method covers the determination of the hy-
Wall Permeameter
draulic conductivity, or the permeability relative to water, of
D 5730 Guide for Site Characterization for Environmental
any porous medium in the laboratory, in particular, the hydrau-
Purposes With Emphasis on Soil, Rock, the Vadose Zone,
lic conductivity for water in subsurface materials, for example,
and Ground Water
soil, sediment, rock, concrete, and ceramic, either natural or
D 6026 Practice for Using Significant Digits in Calculating
artificial, especially in relatively impermeable materials or
and Reporting Geotechnical Test Data
materials under highly unsaturated conditions. This test
method covers determination of these properties using any
3. Terminology
form of steady-state centrifugation (SSC) in which fluid can be
3.1 Definitions—For common definitions of terms in this
applied to a specimen with a constant flux or steady flow
guide, such as porosity, permeability, hydraulic conductivity,
during centrifugation of the specimen. This test method only
water content, and matric potential (matric suction, water
measures advective flow on core specimens in the laboratory.
suction, or water potential), refer to Terminology D 653.
1.2 This standard may involve hazardous materials, opera-
3.2 Definitions of Terms Specific to This Standard:
tions, and equipment. This standard does not purport to
3.2.1 hydraulic steady state—the condition in which the
address all of the safety concerns, if any, associated with its
water flux density remains constant along the conducting
use. It is the responsibility of the user of this standard to
system. This is diagnosed as the point at which both the mass
establish appropriate safety and health practices and deter-
and volumetric water contents of the material are no longer
mine the applicability of regulatory limitations prior to use.
changing.
2. Referenced Documents 3.2.2 SSCM or SSC-UFA—Apparatus to achieve steady-
state centrifugation. The SSCM (steady-state centrifugation
2.1 ASTM Standards:
method) uses a self-contained flow delivery-specimen system
D 420 Guide to Site Characterization for Engineering, De-
2 (1) . The SSC-UFA (unsaturated flow apparatus) uses an
sign, and Construction Purposes
externalpumptodeliverflowtotherotatingspecimen(2).This
D 653 Terminology Relating to Soil, Rock, and Contained
2 test method will describe the SSC-UFA application, but other
Fluids
applications are possible. Specific parts for the SSC-UFA are
D 2216 TestMethodforLaboratoryDeterminationofWater
2 described in Section 6 as an example of a SSC system.
(Moisture) Content of Soil and Rock
3.2.3 steady-state centrifugation—controlled flow of water
D 3740 Practice for Minimum Requirements for Agencies
or other fluid through a specimen while it is rotating in a
Engaged in the Testing and/or Inspection of Soil and Rock
centrifuge, as distinct from water retention centrifugation
as Used in Engineering Design and Construction
methods which measure drainage from a wet specimen by
D 4753 Specification for Evaluating, Selecting, and Speci-
centrifugation with no flow into the specimen.
fying Balances and Scales for Use in Testing Soil, Rock,
3.2.4 water flux density—the flow rate of water through a
and Related Construction Materials
3 2
cross-sectional area per unit time, for example, 5 cm /cm /s,
written as 5 cm/s.
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.21 on GroundWater and
Vadose Zone Investigations. Annual Book of ASTM Standards, Vol 04.09.
Current edition approved Feb. 10, 2000. Published June 2000. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 04.08. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6527–00
3.3 Symbols: can not be effective for measuring unsaturated transport prop-
erties because they do not provide a body force and cannot act
on the entire specimen simultaneously unless the specimen is
K = hydraulic conductivity, cm/s
saturated or near-saturated.Abody force is a force that acts on
3 2
q = water flux density, cm /cm /s or cm/s
every point within the system independently of other forces or
r = distance from axis of rotation, cm
3 properties of the system. High pressures used on saturated
r = dry density, g/cm
systems often induce fracturing or grain rearrangements and
v = rotation speed, radians/s
cause compaction as a result of high-point stresses that are
generated within the specimen. A SSC-UFA does not produce
4. Summary of Test Method
such high-point stresses.
4.1 Using a SSC-UFA is effective because it allows the
5.2 There are specific advantages to using centrifugal force
operator to control the independent variables in Darcy’s Law.
asafluiddrivingforce.Itisabodyforcesimilartogravityand,
Darcy’s Law states that the water flux density equals the
therefore, acts simultaneously over the entire system and
hydraulic conductivity times the fluid driving force (See
independently of other driving forces, for example, gravity or
Section 11). The driving force is fixed by imposing an
matric potential. Additionally, in a SSC-UFA the acceleration
acceleration on the specimen through an adjustable rotation
can dominate any matric potential gradients as the Darcy
speed. The water flux density is fixed by setting the flow rate
drivingforce.Theuseofsteady-statecentrifugationtomeasure
into the specimen with an appropriate constant-flow pump and
steady-state hydraulic conductivities has recently been demon-
dispersing the flow front evenly over the specimen. Thus, the
strated on various porous media (1,2).
specimen reaches the steady-state hydraulic conductivity
5.3 Several issues involving flow in an acceleration field
which is dictated by that combined water flux density and
have been raised and addressed by previous and current
driving force. The operator can impose whatever hydraulic
research (1,4).These studies have shown that compaction from
conductivity is desired within the operational range of rotation
–4 –9 2
acceleration is negligible for subsurface soils at or near their
speeds and flow rates, from 10 cm/s (0.l darcy; 10 cm)to
–11 –8 –16 2
field densities. Bulk densities in these specimens have re-
10 cm/s (10 darcy; 10 cm ). Higher conductivities are
mained constant (60.1 g/cm ) because the specimens are
measured using falling head or constant head methods (3).
already compacted more than the acceleration can affect them.
These methods are also convenient to saturate the specimen.
The notable exception is structured soils. Special arrangements
Following saturation and constant or falling head measure-
must be made to preserve their densities, for example, the use
ments, the specimen is stepwise desaturated in the SSC-UFA
of speeds not exceeding specific equivalent stresses. As an
by increasing the speed and decreasing the flow rate, allowing
example, for most SSC-UFAspecimen geometries, the equiva-
steady state to be reached at each step. Because a relatively
lent pressure in the specimen at a rotation speed of 2500 rpm
largedrivingforceisused,theSSC-UFAcanachievehydraulic
isabout2bar.Ifthespecimensignificantlycompactsunderthis
steady state in a matter of hours for geologic materials, even at
pressure, a lower speed must be used. Usually, only very fine
very low water contents. Sample size is up to about 5-cm
soils at dry bulk densities less than 1.2 g/cm are a problem.
diameter and 6-cm length cores. This test method is distinct
Whole rock, grout, ceramics, or other solids are completely
from water retention centrifugation methods which measure
unaffectedbytheseaccelerations.Precompactionrunsuptothe
simpledrainagefromawetspecimenbycentrifugationwithno
highest speed for that run are performed in the SSC-UFAprior
flow into the specimen. Hydraulic steady state cannot be
to the run to observe any compaction effects.
achieved without flow into the specimen.
5.4 Three-dimensional deviations of the driving force as a
5. Significance and Use
function of position in the specimen are less than a factor of
two. Theoretically, the situation under which unit gradient
5.1 Recent results have demonstrated that direct measure-
conditions are achieved in a SSC-UFA, in which the change in
ments of unsaturated transport parameters, for example, hy-
the matric potential with radial distance equals zero (dc/dr =
draulic conductivity, vapor diffusivity, retardation factors, ther-
0), is best at higher water flux densities, higher speeds, or
mal and electrical conductivities, and water potential, on
coarser grain-size, or combination thereof. This is observed in
subsurface materials and engineered systems are essential for
potential gradient measurements in the normal operational
defensible site characterization needs of performance assess-
range where dc/dr = 0. The worst case occurs at the lowest
ment as well as restoration or disposal strategies. Predictive
water flux densities in the finest-grained materials (1).
models require the transport properties of real systems that can
be difficult to obtain over reasonable time periods using 5.5 There is no sidewall leakage problem in the SSC-UFA
traditional methods. Using a SSC-UFA greatly decreases the for soils. The centrifugal force maintains a good seal between
time required to obtain direct measurements of hydraulic the specimen and the wall. As the specimen desaturates, the
conductivity on unsaturated systems and relatively imperme- increasing matric potential (which still operates in all direc-
able materials. Traditionally, long times are required to attain tions although there is no potential gradient) keeps the water
steady-state conditions and distributions of water because within the specimen, and the acceleration (not being a pres-
normal gravity does not provide a large enough driving force sure) does not force water into any larger pore spaces such as
relative to the low conductivities that characterize highly along a wall. Therefore, capillary phenomena still hold in the
unsaturated conditions or highly impermeable saturated sys- SSC-UFA, a fact which is especially important for fractured or
tems (Test Method D 5084). Pressure techniques sometimes heterogeneous media (2). Cores of solid material such as rock
D6527–00
or concrete, are cast in epoxy sleeves as their specimen holder, of up to 20 000 g (soils are generally run only up to 1 000 g),
and this also prevents sidewall leakage. temperatures can be adjusted from –20 to 150°C. Infusion and
5.6 The SSC-UFA can be used in conjunction with other syringe pumps can provide constant flow rates as low as 0.001
methods that require precise fixing of the water content of a mL/h. Effluent from the specimen is collected in a transparent,
porous material. The SSC-UFA is used to achieve the steady- volumetrically calibrated chamber at the bottom of the speci-
state water content in the specimen and other test methods are men assembly. Using a strobe light, an observer can check the
applied to investigate particular problems as a function of chamber while the specimen is being centrifuged. Two speci-
water content. This has been successful in determining diffu- mens are run at the same time in a SSC-UFA with water
sion coefficients, vapor diffusivity, electrical conductivity, flowingintoeachbymeansoftwofeedlines,thecentralfeedor
monitoring the breakthrough of chemical species (retardation inlet path, and the annular feed. Specific parts are defined as
factor),porewaterextraction,solidscharacterization,andother follows (see Fig. 1):
physical or chemical properties as functions of the water
6.1.1 Specimen Holder—The metal, polysulfone, fiberglass,
content (2,5).
or epoxy shell that contains the soil, rock, cement, or aggregate
5.7 Hydraulic conductivity can be very sensitive to the specimen to be tested.
solutionchemistry,especiallywhenspecimenscontainexpand-
6.1.2 Specimen Cup—The metal canister that contains the
able, or swelling, clay minerals. Water should be used that is
specimen holder. It has a dispersion cap that disperses flow
appropriate to the situation, for example, ground water from
evenly across the top of the specimen. O-ring seals prevent
the site from which the specimen was obtained, or rainwater if
waterflowaroundthesidesofthespecimenholder.Thebottom
an experiment is being performed to investigate infiltration of
of the specimen cup has a cone-shaped spacer that holds the
precipitation into a disposal site. Appropriate antimicrobial
bottom of the holder horizontal and allows effluent to drain out
agents should be used to prevent microbial effects within the
of the specimen cup.
specimen, for example, clogging, but should be chosen with
6.1.3 Bucket—The metal shell that holds the specimen cup
consideration of any important chemical issues in the system.
and screws into the rotor.
Astandardsyntheticporewatersolution,similartothesolution
6.1.4 Effluent Collection Chamber—The plastic graduated
expected in the field, is useful when it is difficult to obtain field
vessel at the end of the specimen cup that collects the effluent
water. Distilled or deionized water is generally not useful
as it exits the specimen cup.
unlesstheresultsaretobecomparedtoothertestsusingsimilar
6.1.5 Rotor—The central aluminum fixture that holds the
water or is specified in pertinent test plans, ASTM test
specimen and bucket and spins on the rotating shaft. Most
methods, or EPA procedures. Distilled water can dramatically
SSC-UFAs have rotors that hold three specimen sizes: a
affect the conductivity of soil and rock specimens that contain
3.33-cm diameter specimen, a 4.44-cm diameter specimen, and
clay minerals, and can induce dissolution/precipitation within
a 20-in. Shelby Tube-sized specimen.
the specimen.
6.1.6 Rotating Seal—The mechanism which connects the
5.8 This test method establishes a dynamic system, and, as
stationary exterior of the system to the rotating interior; the
such, the steady-state water content is usually
...
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