ASTM D6766-20a

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Designation: D6766 − 20 D6766 − 20a
Standard Test Method for
Evaluation of Hydraulic Properties of Geosynthetic Clay
Liners Permeated with Potentially Incompatible Aqueous
Solutions
This standard is issued under the fixed designation D6766; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers laboratory measurement of both flux and hydraulic conductivity (also referred to as coeffıcient of
permeability) of geosynthetic clay liner (GCL) specimens permeated with chemical solutions and leachates utilizing a flexible wall
permeameter. For test measurement of index hydraulic properties of geosynthetic clay liners, refer to Test Method D5887/D5887M.
For hydraulic conductivity compatibility of soils with aqueous chemical solutions and leachates, refer to Test Method D7100.
–5
1.2 This test method may be utilized with GCL specimens that have a hydraulic conductivity less than or equal to 1 × 10 m ⁄s
–3
(1 × 10 cm/s).
1.3 This test method is applicable to GCL products having geotextile backing(s). It is not applicable to GCL products with
geomembrane backing(s), geofilm backing(s), or polymer coating backing(s).
1.4 This test method allows the requester to evaluate the hydraulic properties of a GCL with site-specific or laboratory-prepared
solution under different test conditions; thus, the test method also may be used to check performance or conformance, or both.
1.5 The values stated in SI units are to be regarded as the standard, unless other units are specifically given. By tradition in U.S.
practice, hydraulic conductivity is reported in centimeters per second, although the common SI units for hydraulic conductivity
are meters per second.
1.6 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D854 Test Methods for Specific Gravity of Soil Solids by Water Pycnometer
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D4439 Terminology for Geosynthetics
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D5887/D5887M Test Method for Measurement of Index Flux Through Saturated Geosynthetic Clay Liner Specimens Using a
Flexible Wall Permeameter
D7100 Test Method for Hydraulic Conductivity Compatibility Testing of Soils with Aqueous Solutions
E145 Specification for Gravity-Convection and Forced-Ventilation Ovens
This test method is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.04 on Geosynthetic Clay
Liners.
Current edition approved Jan. 1, 2020May 1, 2020. Published January 2020May 2020. Originally approved in 2002. Last previous edition approved in 20182020 as
D6766 – 18.D6766 – 20. DOI: 10.1520/D6766-20.10.1520/D6766-20A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6766 − 20a
3. Terminology
3.1 Definitions:
3.1.1 flux, n—the rate of discharge of liquid under laminar flow conditions through a unit cross-sectional area of a GCL
specimen at a standard temperature condition (22 6 3 °C).
3.1.2 geosynthetic clay liner (GCL), n—a factory-manufactured geosynthetic hydraulic barrier consisting of clay supported by
geotextiles, geomembranes, or a combination thereof, that are held together by needling, stitching, chemical adhesives, or other
methods.
3.1.3 hydraulic conductivity, k, n—the rate of discharge of liquid under laminar flow conditions through a unit cross-sectional
area of a GCL specimen under a unit hydraulic gradient and standard temperature conditions (22 6 3 °C).
3.1.3.1 Discussion—
The term coeffıcient of permeability is often used instead of hydraulic conductivity, but hydraulic conductivity is used exclusively
in this test method. A more complete discussion of the terminology associated with Darcy’s law is given in the literature.
3.1.4 index test, n—a test procedure that may contain bias, but may be used to establish comparable results with respect to the
property of interest.
3.1.5 pore volume of flow, n—the cumulative quantity of flow into a test specimen divided by the volume of voids in the
specimen.
3.2 For definitions of other terms used in this test method, see Terminologies D653 and D4439.
4. Significance and Use
4.1 This test method applies to one-dimensional, laminar flow of aqueous solutions, such as chemical solutions, landfill
leachate, and contaminated water (from here on referred to as “test liquid”), through saturated/hydrated GCL specimen that is
consolidated and permeated under a prescribed or requested set of conditions.
4.2 This test method assumes that Darcy’s law is valid and that the hydraulic conductivity is essentially unaffected by hydraulic
gradient. The validity of Darcy’s law may be evaluated by measuring the hydraulic conductivity of the specimen at three different
hydraulic gradients; if all measured values are similar (within about 25 %), then Darcy’s law may be taken as valid. However, when
the hydraulic gradient acting on a test specimen is changed, the state of stress will also change and, if the specimen is compressible,
the volume of the specimen will change. Thus, some change in hydraulic conductivity may occur when the hydraulic gradient is
altered, even in cases where Darcy’s law is valid.
4.3 This test method provides tools for determining flux and hydraulic conductivity values for a given GCL under the following
two different scenarios, which should be specified by the requester:
4.3.1 Scenario 1 – Hydrated/Saturated with Water Prior to Contact with Test Liquid—This scenario simulates the field
conditions where the GCL is well hydrated with water prior to contact with actual test liquid. It should be noted that initial degree
of saturation/hydration greatly affects the hydraulic properties of a GCL product. The test has two phases: (Phase 1) hydrate,
saturate, consolidate, and permeate with water as Test Liquid 1, and (Phase 2) switch to permeation with test liquid as Test Liquid
2.
4.3.2 Scenario 2 – Hydrated/Saturated with Test Liquid (Worst Case)—This scenario simulates the field conditions where the
GCL is in contact with test liquid prior to being fully hydrated with water. It should be noted that this scenario may result in higher
flux and hydraulic conductivity values compared to Scenario 1, as chemicals present in test liquid may alter the hydration and
hydraulic properties of a GCL product.
4.4 The apparatus used in this test method is commonly used to determine the hydraulic conductivity of soil specimens.
However, flux values measured in this test are typically much lower than those commonly measured for most natural soils. It is
essential that the leakage rate of the apparatus in this test be less than 10 % of the flux.
5. Apparatus
5.1 Compatibility—All parts in contact with the test liquid(s) shall be checked/verified for long-term compatibility. This can be
established either based on the available information or by in-house testing.
5.2 Hydraulic System—Constant head (Method A), falling head (Methods B and C), or constant rate of flow (Method D) systems
may be utilized provided they meet the criteria outlined as follows:
5.2.1 Constant Head (Method A)—The system must be capable of maintaining constant hydraulic pressures to within 65 % and
shall include means to measure the hydraulic pressures to within the prescribed tolerance. In addition, the head loss across the test
Olson, R. E. and Daniel, D. E., “Measurement of the Hydraulic Conductivity of Fine-Grained Soils,” Symposium on Permeability and Groundwater Contaminant
Transport, ASTM STP 746, ASTM International, 1981, pp. 18–64.
D6766 − 20a
specimen must be held constant to within 65 % and shall be measured with the same accuracy or better. Pressures shall be
measured by a pressure gage, electronic pressure transducer, or any other device of suitable accuracy.
5.2.2 Falling Head (Methods B and C)—The system shall allow for measurement of the applied head loss, thus hydraulic
gradient, to within 65 %. In addition, the ratio of initial head loss divided by final head loss over an interval of time shall be
measured such that this computed ratio is accurate to within 65 %. The head loss shall be measured with a pressure gage,
electronic pressure transducer, engineer’s scale, graduated pipette, or any other device of suitable accuracy. Falling head tests may
be performed with either a falling headwater and constant tailwater elevation (Method B) or a falling headwater and rising tailwater
elevation (Method C).
5.2.3 Constant Rate of Flow (Method D)—The system must be capable of maintaining a constant rate of flow through the
specimen to within +5 %. Flow measurement shall be by calibrated syringe, graduated pipette, or other device of suitable accuracy.
The head loss across the specimen shall be measured to an accuracy of 5 % or better using an electronic pressure transducer or
other device of suitable accuracy. More information on testing with a constant rate of flow is given in the literature.
5.2.4 System De-Airing—The hydraulic system shall be designed to facilitate rapid and complete removal of free air bubbles
from flow lines.
5.2.5 Back Pressure System—The hydraulic system shall have the capability to apply back pressure to the specimen to facilitate
saturation. The system shall be capable of maintaining the applied back pressure throughout the duration of hydraulic conductivity
measurements. The back pressure system shall be capable of applying, controlling, and measuring the back pressure to 5 % or
better of the applied pressure. The back pressure may be provided by a compressed gas supply (see Note 1), a dead weight acting
on a piston, or any other method capable of applying and controlling the back pressure to the tolerance prescribed in this paragraph.
NOTE 1—Application of gas pressure directly to a fluid will dissolve gas in the fluid. Any suitable technique, including separation of gas and liquid
phases with a bladder, may be used to minimize dissolution of gas in the back pressure fluid.
5.3 Flow Measurement System—Both inflow and outflow volumes shall be measured unless the lack of leakage, continuity of
flow, and cessation of consolidation or swelling can be verified by other means. Flow volumes shall be measured by a graduated
accumulator, graduated pipette, vertical standpipe in conjunction with an electronic pressure transducer, or other volume-
measuring device of suitable accuracy.
5.3.1 Flow Accuracy—Required accuracy for the quantity of flow measured over an interval of time is 65 %.
5.3.2 De-Airing and Compliance of the System—The flow measurement system shall contain a minimum of dead space and be
capable of complete and rapid de-airing. Compliance of the system in response to changes in pressure shall be minimized by using
a stiff flow measurement system. Rigid tubing, such as metallic or rigid thermoplastic tubing, shall be used.
5.3.3 Head Losses—Head losses in the tubes, valves, porous end pieces, and filter paper may lead to error. To guard against such
errors, the permeameter shall be assembled with no specimen inside and then the hydraulic system filled. If a constant or falling
head test is to be used, the hydraulic pressures or heads that will be used in testing a specimen shall be applied, and the rate of
flow measured with an accuracy of 5 % or better. This rate of flow shall be at least ten times greater than the rate of flow that is
measured when a GCL specimen is placed inside the permeameter and the same hydraulic pressures or heads are applied. If a
constant rate of flow test is to be used, the rate of flow to be used in testing a specimen shall be supplied to the permeameter and
the head loss measured. The head loss without a specimen shall be less than 0.1 times the head loss when a GCL specimen is
present.
5.4 Permeant Interface Device (Bladder Accumulator)—A permeant interface device shall be used when a hazardous/corrosive
or volatile test liquid, or both, is to be used as the permeant. The permeant interface device shall contain the test liquid in a closed
chamber and allow neither possible contamination of flow measurement and pressure systems nor potential release of chemicals
present in the test liquid to the breathing air, while maintaining the desired test pressures. A schematic diagram of a typical
permeant interface device is shown in Fig. 1. The device consists of mainly a water chamber and a test liquid chamber, which are
separated with a flexible bladder membrane. The device should be checked for leaks at the desired test pressures prior to the testing.
NOTE 2—The suppliers of the apparatus materials in contact with the test liquid (for example, permeant interface device, flexible membrane, and porous
end pieces) may be consulted regarding chemical compatibility with the test liquid prior to testing.
5.5 Permeameter Cell Pressure System—The system for pressurizing the permeameter cell shall be capable of applying and
controlling the cell pressure to within 65 % of the applied pressure. However, the effective stress on the test specimen (which is
the difference between the cell pressure and the pore water pressure) shall be maintained to the desired value with an accuracy of
65 % or better. The device for pressurizing the cell may consist of a reservoir connected to the permeameter cell and partially filled
with de-aired water, with the upper part of the reservoir connected to a compressed gas supply or other source of pressure (see Note
3). The gas pressure shall be controlled by a pressure regulator and measured by a pressure gage, electronic pressure transducer,
or any other device capable of measuring to the prescribed tolerance. A hydraulic system pressurized by dead weight acting on a
piston or any other pressure device capable of applying and controlling the permeameter cell pressure to the tolerance prescribed
in this paragraph may be used.
Olson, H. W., Morin, R. H., and Nichols, R. W., “Flow Pump Applications in Triaxial Testing,” Symposium on Advanced Triaxial Testing of Soil and Rock, ASTM STP
977, ASTM International, 1988, pp. 68–81.
D6766 − 20a
FIG. 1 Schematic Diagram of Permeant Interface Device
NOTE 3—De-aired water is commonly used for the cell fluid to minimize potential for diffusion of air through the membrane into the specimen. Other
fluids, such as oils, which have low gas solubility are also acceptable, provided they do not react with components of the permeameter. Also, use of a
long (approximately 5 to 7 m) tube connecting the pressurized cell liquid to the permeameter cell helps to delay the appearance of air in the cell fluid
and to reduce the flux of dissolved air into the cell.
5.6 Permeameter Cell—An apparatus shall be provided in which the GCL specimen and porous end pieces, enclosed by a
membrane sealed to the cap and base, are subjected to controlled fluid pressures. A schematic diagram of a typical cell is shown
in Fig. 2.
5.6.1 The permeability cell may allow for observation of changes in height of the GCL specimen, either by observation through
the cell wall using a cathetometer or other instrument, or by monitoring of either a loading piston or an extensometer extending
through the top plate of the cell bearing on the top cap and attached to a dial indicator or other measuring device. The piston or
extensometer should pass through a bushing and seal incorporated into the top plate and shall be loaded with sufficient force to
compensate for the cell pressure acting over the cross-sectional area of the piston where it passes through the seal. If deformations
are measured, the deformation indicator shall be a dial indicator or cathetometer graduated to 0.3 mm (0.01 in.) or better and having
an adequate travel range. Any other measuring device meeting these requirements is acceptable.
5.6.2 In order to facilitate gas removal, and thus saturation of the hydraulic system, four drainage lines leading to the specimen,
two each to the base and top cap, are recommended. The drainage lines shall be controlled by no-volume-change valves, such as
ball valves, and shall be designed to minimize dead space in the lines.
5.7 Top Cap and Base—An impermeable, rigid top cap and base shall be used to support the specimen and provide for
transmission of permeant liquid to and from the specimen. The diameter or width of the top cap and base shall be equal to the
diameter or width of the specimen 65 %. The base shall prevent leakage, lateral motion, or tilting, and the top cap shall be
designed to receive the piston or extensometer, if used, such that the piston-to-top cap contact area is concentric with the cap. The
surface of the base and top cap that contacts the membrane to form a seal shall be smooth and free of scratches.
5.8 Flexible Membranes—The flexible membrane used to encase the specimen shall provide reliable protection against leakage.
The membrane shall be carefully inspected prior to use and if any flaws or pinholes are evident, the membrane shall be discarded
(see Note 4). To minimize restraint of the specimen, the diameter or width of the unstretched membrane shall be between 90 and
95 % of that of the specimen. The membrane shall be sealed to the specimen base and cap with rubber O-rings for which the
unstressed inside diameter or width is less than 90 % of the diameter of width of the base and cap, or by any other method that
will produce an adequate seal.
NOTE 4—Membranes may be tested for flaws by placing them around a form sealed at both ends with rubber O-rings, subjecting them to a small air
D6766 − 20a
FIG. 2 Schematic Diagram of Permeameter Cell
pressure on the inside, and then dipping them into water. If air bubbles come up from any point on the membrane, or if any visible flaws are observed,
the membrane shall be discarded. In some cases, when there are no compatible membranes available, the specimen may be wrapped by a very thin and
flexible sheet/film/tape of chemically resistive and compatible material such as TFE-fluorocarbon prior to placement of the flexible membrane.
5.9 Porous End Pieces—The porous end pieces shall be of silicon carbide, aluminum oxide, or other material that is not attacked
by the specimen or permeant liquid. The end pieces shall have plane and smooth surfaces and be free of cracks, chips, and
nonuniformities. They shall be checked regularly to ensure that they are not clogged.
5.9.1 The porous end pieces shall be the same diameter or width (65 %) as the specimen, and the thickness shall be sufficient
to prevent breaking.
5.9.2 The hydraulic conductivity of the porous end pieces shall be significantly greater than that of the specimen to be tested.
The requirements outlined in 5.3.3 ensure this.
5.10 Filter Paper—To prevent intrusion of material into the pores of the porous end pieces, one or more sheets of filter paper
shall be placed between the top and bottom porous end pieces and the specimen (see Note 5). The filter paper shall have a
negligibly small hydraulic impedance. The requirements outlined in 5.3.3 ensure that the impedance is small.
NOTE 5—The type of filter paper recommended is Whatman No. 1 (or equivalent), that has a particle retention capability greater than 11 μm.
NOTE 6—For solutions with high suspended solids levels, clogging can be an important consideration. In these cases, nonwoven geotextiles can be used
on both sides of the GCL specimen, in lieu of porous stones and filter paper that can be more susceptible to particulate clogging. Some laboratories first
pass high suspended solids solutions through a 100-mesh stainless steel screen to filter out solids.
5.11 Trimming Equipment—Specific equipment for trimming the specimen to the desired diameter will vary depending on
quality and characteristics of the sample and the procedure used to prepare the specimen. The following items, however, are
commonly used: razor knife, cutting dyes, carpet knife, and scissors.
5.12 Devices for Measuring the Dimensions of the Specimen—Devices used to measure the dimensions of the specimen shall
be capable of measuring to the nearest 0.3 mm (0.01 in.) or better and shall be constructed such that their use will not disturb the
specimen.
5.13 Balance—The balance shall be suitable for determining the mass of the specimen and shall be selected as discussed in
Guide D4753. The mass of specimens less than 100 g shall be determined to the nearest 0.01 g. The mass of specimens 100 g or
larger shall be determined to the nearest 0.1 g. The mass of specimens larger than 1000 g shall be determined to the nearest 1.0 g.
5.14 Equipment for Mounting the Specimen—Equipment for mounting the specimen in the permeameter cell shall include a
membrane expander or cylinder, and rings for expanding and placing O-rings on the base and top cap to seal the membrane.
5.15 Vacuum Pump—To assist with de-airing of water or, if applicable, the test liquid.
5.16 Temperature Maintaining Device—The temperature of the permeameter, test specimen, and reservoir(s) of test liquid shall
not vary more than 63 °C (65.7 °F). Normally, this is accomplished by performing the test in a room with a temperature of 22
6 3 °C. If such a room is not available, the apparatus shall be placed in a water bath, insulated chamber, or other device that
maintains a temperature within the specified tolerance. The temperature shall be periodically measured and recorded.
D6766 − 20a
5.17 Water Content Containers—The containers shall be in accordance with Test Methods D2216.
5.18 Drying Oven—The oven shall be in accordance with Specification E145.
6. Reagents
6.1 Deionized Water:
6.1.1 De-Aired Water—To aid in saturating the test specimen as much as possible, de-aired water should be used when
appropriate. Water can be de-aired by boiling, by spraying a fine mist of water into an evacuated vessel attached to a vacuum
source, or by forceful agitation of water in a container attached to a vacuum source. If boiling is used, care shall be taken not to
evaporate an excessive amount of liquid which can lead to a larger mineral concentration in the water than desired. To prevent
dissolution of air back into the water, de-aired water shall not be exposed to air for prolonged periods.
6.2 Test Liquids:
6.2.1 The test liquid is the liquid used for permeation of the test specimen and it may be used in hydrating/saturating the
specimen.
6.2.2 The test liquids should be specified and, if available, supplied along with chemical composition by the requester for both
Test Scenarios 1 and 2.
6.2.3 Test liquids which may contain volatile chemicals or may cause any potential hazards during the de-airing process should
not be de-aired, even when the test liquid is used to hydrate/saturate the specimen.
NOTE 7—Samples containing separate phase liquids should be left in a quiescent state for 24 h, to allow the non-aqueous phases to separate from the
aqueous phase. The aqueous phase can then be decanted and used as the permeant liquid.
7. Test Specimen Preparation
7.1 Inspe
...