ASTM D7664-10(2018)e1

Standard Test Methods for Measurement of Hydraulic Conductivity of Unsaturated Soils

SIGNIFICANCE AND USE
5.1 The hydraulic conductivity function (HCF) is fundamental to hydrological characterization of unsaturated soils and is required for most analyses of water movement in unsaturated soils. For instance, the HCF is a critical parameter to analyze the movement of water during infiltration or evaporation from soil specimens. This is relevant to the evaluation of water movement in landfill cover systems, stiffness changes in pavements due to water movement, recharge of water into aquifers, and extraction of pore water from soils for sampling.  
5.2 Examples of HCFs reported in the technical literature are shown in Fig. 1(a), Fig. 1(b), and Fig. 1(c), for clays, silts, and sands, respectively. The decision to report a HCF in terms of suction or volumetric water content depends on the test method and instruments used to measure the HCF. The methods in Categories A and C will provide a HCF in terms of either suction or volumetric water content, while the methods in Category B will provide a HCF in terms of suction.
FIG. 1 Experimental HCFs for Different Soils: (a) k-ψ for Clays; (b) k-θ for Silts; (c) k-θ for Sands (3-14)  
5.3 A major assumption involved in measurement of the hydraulic conductivity is that it is used to quantify movement of water in liquid form through unsaturated soils (that is, it is the coefficient of proportionality between liquid water flow and hydraulic gradient). Water can also move through soil in vapor form, but different mechanisms govern impedance of a soil to water vapor flow (diffusion). Accordingly, the HCF is only applicable in engineering practice for degrees of saturation in which the water phase is continuous (that is, no pockets of “unconnected” water). Although this depends on the soil type and texture, this approximately corresponds to degrees of saturation greater than 50 to 60 %.  
5.4 The HCFs of soils may be sensitive to the porosity, soil structure, compaction (compaction gravimetric water content and dry unit weight), effe...
SCOPE
1.1 These test methods cover the quantitative measurement of data points suitable for defining the hydraulic conductivity functions (HCF) of unsaturated soils. The HCF is defined as either the relationship between hydraulic conductivity and matric suction or that between hydraulic conductivity and volumetric water content, gravimetric water content, or the degree of saturation. Darcy’s law provides the basis for measurement of points on the HCF, in which the hydraulic conductivity of a soil specimen is equal to the coefficient of proportionality between the flow rate of water through the specimen and the hydraulic gradient across the specimen. To define a point on the HCF, a hydraulic gradient is applied across a soil specimen, the corresponding transient or steady-state water flow rate is measured (or vice versa), and the hydraulic conductivity calculated using Darcy’s law is paired with independent measurements of matric suction or volumetric water content in the soil specimen.  
1.2 These test methods describe a family of test methods that can be used to define points on the HCF for different types of soils. Unfortunately, there is no single test that can be applied to all soils to measure the HCF due to testing times and the need for stress control. It is the responsibility of the requestor of a test to select the method that is most suitable for a given soil type. Guidance is provided in the significance and use section of these test methods.  
1.3 Similar to the Soil Water Retention Curve (SWRC), defined as the relationship between volumetric water content and matric suction, the HCF may not be a unique function. Both the SWRC and HCF may follow different paths whether the unsaturated soil is being wetted or dried. A test method should be selected which replicates the flow process occurring in the field.  
1.4 These test methods describe three categories of methods (Categories A through C) for direct measurement...

General Information

• Status: Published
• Publication Date: 30-Sep-2010
• ICS: 13.080.40 - Hydrological properties of soils
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.04 - Hydrologic Properties and Hydraulic Barriers

Relations

• Replaces: ASTM D7664-10 - Standard Test Methods for Measurement of Hydraulic Conductivity of Unsaturated Soils
• Effective Date: 01-Oct-2010
• Refers: ASTM D5101-23 - Standard Test Method for Measuring the Filtration Compatibility of Soil-Geotextile Systems
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D854-23 - Standard Test Methods for Specific Gravity of Soil Solids by the Water Displacement Method
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D2487-17e1 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D4318-17 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D4318-17e1 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D5101-12(2017) - Standard Test Method for Measuring the Filtration Compatibility of Soil-Geotextile Systems
• Effective Date: 15-Feb-2017
• Refers: ASTM D6836-16 - Standard Test Methods for Determination of the Soil Water Characteristic Curve for Desorption Using Hanging Column, Pressure Extractor, Chilled Mirror Hygrometer, or Centrifuge
• Effective Date: 15-Nov-2016
• Refers: ASTM D5084-16 - Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter
• Effective Date: 01-Aug-2016
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D5101-12 - Standard Test Method for Measuring the Filtration Compatibility of Soil-Geotextile Systems
• Effective Date: 01-Jul-2012

Overview

ASTM D7664-10(2018)e1 is the internationally recognized ASTM standard for test methods used to measure the hydraulic conductivity of unsaturated soils. Hydraulic conductivity is a critical parameter in the field of geoenvironmental and geotechnical engineering, as it governs the movement of water through soil in situations where the soil is not fully saturated. This standard provides detailed guidance on methods to quantitatively determine the hydraulic conductivity function (HCF), which describes how conductivity varies in relation to factors such as matric suction or water content.

These methods are fundamental for hydrological characterization, influencing the analysis and design of landfill covers, road pavements, groundwater recharge, and environmental containment systems. The standard addresses the need to accurately replicate field processes in laboratory testing and acknowledges that no single test covers all soil types or site conditions.

Key Topics

• Hydraulic Conductivity Function (HCF): The relationship between hydraulic conductivity and either matric suction, volumetric water content, gravimetric water content, or degree of saturation. The HCF is essential for modeling water flow in unsaturated conditions.
• Test Methods Categories:
  • Category A (Column Tests): Utilizes rigid wall permeameters to measure changes in water content or suction profiles during imposed flow processes.
  • Category B (Axis Translation Tests): Employs high air entry porous discs in oedometer or flexible wall permeameter setups to measure flow and suction.
  • Category C (Centrifuge Permeameter Tests): Uses a spinning centrifuge to expedite steady-state flow through soil columns and measure conductivity.
• Measurement Principles: All test methods are based on Darcy’s law, which relates water flow rate through a specimen to the hydraulic gradient, allowing the calculation of hydraulic conductivity.
• Applicability and Limitations: Not all methods are suitable for every soil type. Proper method selection depends on soil characteristics (such as plasticity and grain size), test duration constraints, and practical considerations for laboratory and field conditions.
• Reporting Units: Hydraulic conductivity is typically reported in meters per second [m/s] and suction in kilopascals [kPa], in line with SI unit standards.

Applications

ASTM D7664-10(2018)e1 is applicable in a variety of engineering and environmental situations where understanding the movement of water through partially saturated soils is vital:

• Environmental Protection: Design and analysis of landfill covers and barriers to minimize leachate migration.
• Geotechnical Engineering: Assessment of pavement subgrades and embankments where moisture variation affects load-bearing properties and durability.
• Groundwater Recharge: Modeling water infiltration to predict recharge rates for aquifers.
• Soil Remediation: Extraction of pore water for contamination analysis and remediation monitoring.
• Research and Education: Fundamental studies of soil-water relationships and their implications on infrastructure and environmental systems.

This standard enables consistency and accuracy in laboratory-based assessments, supporting reliable simulation of field-relevant hydrologic processes.

Related Standards

Understanding and applying ASTM D7664-10(2018)e1 is enhanced by referencing related ASTM standards:

• ASTM D653: Standard Terminology Relating to Soil, Rock, and Contained Fluids
• ASTM D2216: Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock
• ASTM D2487: Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• ASTM D4318: Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• ASTM D5084: Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter
• ASTM D6836: Test Methods for Determination of the Soil Water Characteristic Curve for Desorption

Integrating these standards with ASTM D7664 ensures comprehensive characterization of soil hydraulic properties for advanced geotechnical and environmental engineering practices.

Standards Content (Sample)

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.
´1
Designation: D7664 − 10 (Reapproved 2018)
Standard Test Methods for
Measurement of Hydraulic Conductivity of Unsaturated
Soils
This standard is issued under the fixed designation D7664; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Reapproval with changes editorially added in October 2018.
1. Scope 1.4 Thesetestmethodsdescribethreecategoriesofmethods
(Categories A through C) for direct measurement of the HCF.
1.1 These test methods cover the quantitative measurement
CategoryA(column tests) involves methods used to define the
of data points suitable for defining the hydraulic conductivity
HCF using measured one-dimensional profiles of volumetric
functions (HCF) of unsaturated soils. The HCF is defined as
water content or suction with height in a column of soil
either the relationship between hydraulic conductivity and
compacted into a rigid wall permeameter during imposed
matric suction or that between hydraulic conductivity and
transient and steady-state water flow processes. Different
volumetric water content, gravimetric water content, or the
means of imposing water flow processes are described in
degree of saturation. Darcy’s law provides the basis for
separate methods within Category A. Category B (axis trans-
measurement of points on the HCF, in which the hydraulic
lation tests) involves methods used to define the HCF using
conductivity of a soil specimen is equal to the coefficient of
outflow measurements from a soil specimen underlain by a
proportionality between the flow rate of water through the
saturated high-air entry porous disc in a permeameter during
specimen and the hydraulic gradient across the specimen. To
imposed transient water flow processes. The uses of rigid-wall
define a point on the HCF, a hydraulic gradient is applied
or flexible-wall permeameters are described in separate meth-
across a soil specimen, the corresponding transient or steady-
ods within Category B. Category C (centrifuge permeameter
state water flow rate is measured (or vice versa), and the
test) includes a method to define the HCF using measured
hydraulic conductivity calculated using Darcy’s law is paired
volumetricwatercontentorsuctionprofilesinacolumnofsoil
with independent measurements of matric suction or volumet-
confined in a centrifuge permeameter during imposed steady-
ric water content in the soil specimen.
statewaterflowprocesses.Themethodsinthisstandardcanbe
1.2 These test methods describe a family of test methods
used to measure hydraulic conductivity values ranging from
thatcanbeusedtodefinepointsontheHCFfordifferenttypes
the saturated hydraulic conductivity of the soil to approxi-
of soils. Unfortunately, there is no single test that can be -11
mately 10 m/s.
appliedtoallsoilstomeasuretheHCFduetotestingtimesand
1.5 The methods of data analysis described in these test
the need for stress control. It is the responsibility of the
methods involve measurement of the water flow rate and
requestor of a test to select the method that is most suitable for
hydraulic gradient, and calculation of the hydraulic conductiv-
a given soil type. Guidance is provided in the significance and
ity using Darcy’s law (direct methods) (1). Alternatively,
use section of these test methods.
inversemethodsmayalsobeusedtodefinetheHCF (2).These
1.3 Similar to the Soil Water Retention Curve (SWRC),
employ an iterative, regression-based approach to estimate the
defined as the relationship between volumetric water content
hydraulicconductivitythatasoilspecimenwouldneedtohave
and matric suction, the HCF may not be a unique function.
given a measured water flow response. However, as they
Both the SWRC and HCF may follow different paths whether
require specialized engineering analyses, they are excluded
the unsaturated soil is being wetted or dried. A test method
from the scope of these test methods.
should be selected which replicates the flow process occurring
1.6 These test methods apply to soils that do not change
in the field.
significantly in volume during changes in volumetric water
content or suction, or both (that is, expansive clays or collaps-
ing soils). This implies that these methods should be used for
ThesetestmethodsareunderthejurisdictionofASTMCommitteeD18onSoil
sands, silts, and clays of low plasticity.
and Rock and are the direct responsibility of Subcommittee D18.04 on Hydrologic
Properties and Hydraulic Barriers.
Current edition approved Oct. 1, 2010. Published November 2018. Originally
approved in 2010. Last previous edition approved in 2010 as D635–10. DOI: Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
10.1520/D7664–10R18E01. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D7664 − 10 (2018)
1.7 The methods apply only to soils containing two pore D3740Practice for Minimum Requirements for Agencies
fluids: a gas and a liquid. The liquid is usually water and the Engaged in Testing and/or Inspection of Soil and Rock as
gas is usually air. Other fluids may also be used if requested. Used in Engineering Design and Construction
Caution shall be exercised if the liquid being used causes D4318Test Methods for Liquid Limit, Plastic Limit, and
shrinkage or swelling of the soil. Plasticity Index of Soils
D5084Test Methods for Measurement of Hydraulic Con-
1.8 The units used in reporting shall be SI units in order to
ductivity of Saturated Porous Materials Using a Flexible
be consistent with the literature on water flow analyses in
Wall Permeameter
unsaturated soils. The hydraulic conductivity shall be reported
D5101Test Method for Measuring the Filtration Compat-
in units of [m/s], the matric suction in units of [kPa], the
3 3
ibility of Soil-Geotextile Systems
volumetric water content in [m /m ] or [%], and the degree of
3 3 D6026Practice for Using Significant Digits in Geotechnical
saturation in [m /m ].
Data
1.9 All observed and calculated values shall conform to the
D6527Test Method for Determining Unsaturated and Satu-
guideforsignificantdigitsandroundingestablishedinPractice
rated Hydraulic Conductivity in Porous Media by Steady-
D6026. The procedures in Practice D6026 that are used to 4
State Centrifugation (Withdrawn 2017)
specify how data are collected, recorded, and calculated are
D6836Test Methods for Determination of the Soil Water
regarded as the industry standard. In addition, they are repre-
Characteristic Curve for Desorption Using Hanging
sentative of the significant digits that should generally be
Column, Pressure Extractor, Chilled Mirror Hygrometer,
retained. The procedures do not consider material variation,
or Centrifuge
purpose for obtaining the data, special purpose studies, or any
considerations for the objectives of the user. Increasing or
3. Terminology
reducing the significant digits of reported data to be commen-
3.1 Definitions:
surate with these considerations is common practice. Consid-
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
eration of the significant digits to be used in analysis methods
to Terminology D653.
for engineering design is beyond the scope of these test
3.2 Definitions of Terms Specific to This Standard:
methods.
-1
3.2.1 airentrysuction,ψ ,(FL ),n—thesuctionrequiredto
a
1.10 This standard does not purport to address all of the
introduceairinto(andthrough)theporesofasaturatedporous
safety concerns, if any, associated with its use. It is the
material (soil or porous plate).
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.2.2 angular velocity,ω, (radians/T), n—the angular speed
mine the applicability of regulatory limitations prior to use.
of a centrifuge.
1.11 This international standard was developed in accor-
3.2.3 axis translation, n—the principle stating that a matric
dance with internationally recognized principles on standard-
suction ψ can be applied to a soil by controlling the pore air
ization established in the Decision on Principles for the
pressure u and the pore water pressure u so that the
a w
Development of International Standards, Guides and Recom-
difference between the pore air and water pressures equals the
mendations issued by the World Trade Organization Technical
desired matric suction, that is, ψ=u −u .
a w
Barriers to Trade (TBT) Committee.
3.2.4 capacitance probe, n—a tool used to infer the volu-
2. Referenced Documents
metric water content of an unsaturated soil through measure-
ment of the capacitance of a probe embedded within the soil.
2.1 ASTM Standards:
D422Test Method for Particle-SizeAnalysis of Soils(With-
3.2.5 centrifuge permeameter, n—a system having the pur-
drawn 2016)
poses of holding a soil specimen in a centrifuge, applying
D653Terminology Relating to Soil, Rock, and Contained
inflow rates to the top of the soil specimen, and collecting
Fluids
outflow from the bottom of the soil specimen.
D854Test Methods for Specific Gravity of Soil Solids by
3 -3
3.2.6 degree of saturation S , (L L ),n—the ratio of: (1)
r
Water Pycnometer
thevolumeofwaterinagivensoilorrockmass,to (2)thetotal
D1587Practice for Thin-Walled Tube Sampling of Fine-
volume of intergranular space (voids).
Grained Soils for Geotechnical Purposes
3.2.7 flexible-wall permeameter, n—a setup used to control/
D2216TestMethodsforLaboratoryDeterminationofWater
measuretheflowandhydraulicgradientacrossasoilspecimen
(Moisture) Content of Soil and Rock by Mass
contained within a latex membrane.
D2487Practice for Classification of Soils for Engineering
Purposes (Unified Soil Classification System)
3.2.8 g-level, N , (D), n—the ratio of the acceleration of
r,mid
gravity g to the centripetal acceleration, equal to ω (r -z )/g,
0 mid
where r is equal to the radius at the bottom of the centrifuge
3 0
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
permeameter, and z is the distance from the base of the soil
mid
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on specimen to its mid-height.
the ASTM website.
3.2.9 high air-entry porous disc, n—a disc made of metal,
The last approved version of this historical standard is referenced on
www.astm.org. ceramic, or other porous material that can transmit water and
´1
D7664 − 10 (2018)
has an air entry pressure exceeding the highest matric suction capable of lifting the liquid. In tests run using this standard, h
v
to be applied during a test. is negligible compared with the other components.
3 -3
3.2.21 volumetric water content, θ, (L L or %),n—the
3.2.10 high air-entry porous membrane, n—a porous poly-
ratioofthevolumeofwatercontainedintheporespacesofsoil
meric membrane that transmits water and has an air entry
or rock to the total volume of soil or rock.
suction greater than the highest suction to be applied during a
-1
test.
3.2.22 water discharge velocity, v, (LT ),n—rate of dis-
-1
chargeofwaterthroughaporousmediumperunitoftotalarea
3.2.11 hydraulic conductivity, k, (LT ) ,n—the rate of
perpendicular to the direction of flow.
discharge of water under laminar flow conditions through a
unit cross-sectional area of porous medium under a unit
3.2.23 water flow rate, Q, n—the volumetric rate of flow of
hydraulicgradientandstandardtemperatureconditions(20°C).
water through a soil specimen.
The hydraulic conductivity is defined as the coefficient of
proportionality between the water discharge velocity and the
4. Summary of Test Method
spatial gradient in hydraulic head across a saturated or unsatu-
4.1 Method A—Column Tests:
rated soil specimen, as follows:
4.1.1 CategoryAincludesfourmethods(MethodsA1toA4)
v
which involve measurement of changes in volumetric water
k 5 (1)
i
contentandsuctionoverspaceandtimeinasoilspecimenheld
within a horizontally- or vertically-oriented column during
3.2.12 hydraulic conductivity function (HCF),
one-dimensional water flow.
n—relationship between the hydraulic conductivity and the
4.1.2 Method A1 involves downward infiltration of water
matric suction, volumetric water content, or degree of satura-
onto the surface of an initially unsaturated soil specimen,
tion.
MethodA2 involves upward imbibition of water from the base
3.2.13 hydraulic gradient, i, (D), n—the change in total
of an initially unsaturated soil specimen, Method A3 involves
hydraulic head, ∆h, per unit distance Lin the direction of fluid
downward drainage of water from an initially saturated soil
flow, or i = ∆h/L.
specimen, and MethodA4 involves evaporation of water from
-1
3.2.14 infiltration rate, (LT ),n—the value of the water
an initially saturated soil specimen.
discharge velocity applied to the surface of a soil specimen to 4.1.3 MethodsA1toA4canbeusedforawiderangeofsoil
simulate infiltration.
types, but their practical application will depend on the time
-2 required to impose water flow through the soil specimen.
3.2.15 matric suction,ψ, (FL ),n—the difference between
Methods A1 through A4 shall not be used for soils with high
theporegaspressureu andtheporewaterpressureu insoil;
g w
plasticitybecauseofprohibitivetestingtimes,potentialforsoil
thatisψ=u −u ,whichyieldsapositivevalue.Theporegas
g w
cracking, side-wall leakage, and prohibitive column lengths to
in this test method is assumed to be air under pressure u,so
a
avoid outflow boundary effects. Methods A1 and A2 shall be
ψ=u −u .
a w
used for fine-grained sands and for low-plasticity silts. In the
3.2.16 pressure chamber, n—a setup that involves a rigid-
caseofMethodA1,coarse-grainedsoilsmaybesubjecttoflow
wall oedometer cell contained within a pressure vessel. This
throughpreferentialpathways,whileinthecaseofMethodA2,
chamber is used to independently apply a gas pressure to one
coarse-grained soils may not have sufficient capillary rise.
sideandwaterpressuretotheothersideofasoilspecimenheld
Methods A1 and A2 can be used to measure k values
within the oedometer in order to impose an average value of
corresponding to matric suction values ranging from 0 to 80
matric suction on the specimen.
kPa (12 psi) the upper limit on common matric suction
instrumentation). Method A3 shall be used with fine- or
3.2.17 soil-water retention curve (SWRC), n—relationship
coarse-grained sands. MethodA3 shall not be used for silts or
between matric suction and volumetric water content.
claysbecauseofdifficultiesinsaturatingthesoilspecimenand
3.2.18 tensiometer, n—a tool used to measure the matric
the long time required for gravity drainage to occur. Method
suction in soil by measuring the negative water pressure in a
A3 can be used to measure k values corresponding to matric
waterreservoirinequilibriumwithasoilviaasaturatedporous
suction values from 0 to 200 kPa (29 psi). MethodA4 shall be
disc.
used for any soil with the exception of clays of high plasticity
that show significant cracking during drying. Method A4 can
3.2.19 time domain reflectometer (TDR), n—a tool used to
infer the volumetric water content of an unsaturated soil be used to measure k values corresponding to matric suction
through measurement of the travel time of an electromagnetic values from 0 to 1000 kPa (145 psi) (or higher). Method A4
pulse through a metallic, shielded rod embedded within the shall not be used for silts or clays because of the potential for
soil. formation of low permeability surface crusts. The best-suited
soils for Methods A1 through A4 are summarized in Table 1.
3.2.20 total hydraulic head, h, n—the sum of three compo-
nents at a point: (1) elevation head, h , which is equal to the 4.2 Category B—Axis Translation Tests:
e
elevation of the point above a datum; (2) pressure head, h , 4.2.1 Category B includes two methods (Methods B1 and
p
which is the height of a column of static water that can be B2), which both involve measurement of outflow from a soil
supported by the static pressure at the point; and (3) velocity specimen during an axis translation test (a test commonly used
head, h , which is the height the kinetic energy of the liquid is to measure the SWRC—see Test Methods D6836). An axis
v
´1
D7664 − 10 (2018)
TABLE 1 Guide for Selection of HCF Test Methods
Testing Time
Test Best-Suited Field
Description Equipment Advantages Disadvantages for Silty Clays
Method Soils Application
(1, 3, 4, 5, 6, 7)
A1 Infiltration column Fine sands and low Column, flow Infiltration Straightforward Long testing time, Several weeks
plasticity silts (4, 7) control, water analysis preferential
content and suction pathways, no stress
instrumentation control
A2 Imbibition column Fine sands and low Column, Rising of a water Straightforward Long testing time Several weeks
plasticity silts manometer, table analysis for fine grained
Instrumentation soils, nonuniform
wetting
A3 Drainage column Fine- or coarse- Column, Lowering of a water Straightforward Nonuniform 1-2 weeks
grained sands manometer, table analysis drainage
instrumentation
A4 Evaporation column All soils except Column, heat lamp, Evaporation from Straightforward Varying boundary 1-2 weeks
clays of high fan, Instrumentation soil surface analysis conditions,
plasticity (6) desiccation may
cause nonuniform
drying
B1 Axis translation with Fine-grained soils Oedometer with Wetting and drying Oedometric stress Impedance of 1-2 weeks
rigid wall (3, 8, 7) high air entry with continuous control, volume change porous stone
permeameter porous disc, outflow water phase measurements
measurement
B2 Axis translation with Fine-grained soils Permeameter with Wetting and drying Isotropic stress control, Impedance of 1-2 weeks
flexible wall (8) high air entry with continuous volume change porous stone
permeameter porous disc, outflow water phase measurements
control
C Centrifuge Coarse-grained Centrifuge Similar to column Fast testing time, best Equipment Less than 1 week
permeameter soils and low permeameter, tests, but better for hysteresis requirements
plasticity fine instrumentation suited for wetting/
grained soils (7) drying
translation test involves placing a soil specimen on a water- 4.3.1 Category C includes one test method (Method C)
saturated high air-entry porous disc or membrane, then apply- which involves infiltration of water through a soil specimen
ing a matric suction to the soil specimen by imposing an air within a permeameter spinning in a centrifuge. The centrifuge
pressure on the top side of the specimen and a water pressure isusedtoimposehydraulicgradientsbyincreasingtheeffectof
on bottom side of the high air-entry porous disc. the elevation head, which reduces the time required to reach
4.2.2 Method B1 involves performing an axis translation steady-state water flow through the soil specimen when com-
test in a pressure chamber with the soil specimen held within pared with column infiltration tests (Method A1). Method C
a rigid-wall oedometer. Method B2 involves performing an shall be used for coarse-grained soils and low-plasticity fine-
axistranslationtestinaflexible-wallpermeameterwiththesoil grained soils. Method C can be used to measure k values
specimen held within a flexible latex membrane. Methods B1 corresponding to suction values between 0 and 200 kPa (29
and B2 are best suited for fine-grained soils. Methods B1 and psi).
B2 can be used to measure k values corresponding to suctions
5. Significance and Use
ranging from 0 to 1000 kPa (145 psi).
5.1 The hydraulic conductivity function (HCF) is funda-
4.2.3 The HCF may be defined with the axis translation
mentaltohydrologicalcharacterizationofunsaturatedsoilsand
technique by measuring the outflow when a hydraulic gradient
isrequiredformostanalysesofwatermovementinunsaturated
is applied to an unsaturated soil specimen (that is, by applying
soils. For instance, the HCF is a critical parameter to analyze
an air pressure to one side of the soil specimen and a water
the movement of water during infiltration or evaporation from
pressure to the opposite side).
soil specimens. This is relevant to the evaluation of water
4.2.4 The axis-translation technique can only be used to
movement in landfill cover systems, stiffness changes in
provide, at best, an approximation of the HCF of an unsatu-
pavements due to water movement, recharge of water into
ratedsoil.Thenonuniformityinsuctionacrosstheheightofthe
aquifers, and extraction of pore water from soils for sampling.
soil specimen (zero at the boundary with the high-air entry
porous disc, and greater than zero at the top of the specimen)
5.2 Examples of HCFs reported in the technical literature
implies that the matric suction corresponding to the measured
areshowninFig.1(a),Fig.1( b),andFig.1(c),forclays,silts,
hydraulic conductivity is approximate.Also, the impedance to
and sands, respectively. The decision to report a HCF in terms
flow due to the high-air entry porous disc affects the measured
of suction or volumetric water content depends on the test
hydraulic conductivity. Finally, air diffusion through the high
method and instruments used to measure the HCF. The
air-entry porous disc or membrane complicates accurate mea-
methods in CategoriesAand C will provide a HCF in terms of
surement of outflow volumes. Nevertheless, the technique
either suction or volumetric water content, while the methods
provides a means to measure the HCF using commonly
in Category B will provide a HCF in terms of suction.
available equipment.
5.3 A major assumption involved in measurement of the
4.3 Category C—Centrifuge Permeameter Test: hydraulic conductivity is that it is used to quantify movement
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FIG. 1 Experimental HCFs for Different Soils: (a) k-ψ for Clays; (b) k-θ for Silts; (c) k-θ for Sands (3-14)
of water in liquid form through unsaturated soils (that is, it is applicable in engineering practice for degrees of saturation in
thecoefficientofproportionalitybetweenliquidwaterflowand which the water phase is continuous (that is, no pockets of
hydraulic gradient).Water can also move through soil in vapor “unconnected” water). Although this depends on the soil type
form, but different mechanisms govern impedance of a soil to and texture, this approximately corresponds to degrees of
water vapor flow (diffusion). Accordingly, the HCF is only saturation greater than 50 to 60%.
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5.4 The HCFs of soils may be sensitive to the porosity, soil 6.1.2 The column shall be constructed from non-reactive
structure, compaction (compaction gravimetric water content metals, acrylic, or PVC, although it is often advantageous for
and dry unit weight), effective stress, temperature, and testing the column material to be transparent to visualize water
flow path (wetting or drying). However, not all engineering movementinthesoilspecimen.Asturdyworkingenvironment
problemsneedtoaccountfortheeffectsofthesevariables.Out shall be provided for the column in the case that the soil
of the test methods listed in Section 4, there is not a single specimen is prepared using compaction, wet tamping, or
method that is best suited to measure the effects of all of these pluviation. A means of affixing the column to the outflow
variables.Inaddition,thedifferenttestsmayhaveawiderange supportplatetopreventleakagefromthebottomofthecolumn
in testing times. Table 1 is provided as a guide for selection of shallbeprovided.Columnsmaybeattachedtoasupportframe
thebesttestforagivensoilandapplication.Testtimesforlow using tensioned wires or rods. If wires are used, they may be
plasticity, silty clays are provided as a baseline reference. attached to eye bolts on the support frame and to hook bolts
Testingtimesforcoarse-grainedsoilsaretypicallyontheorder placedoverthetopedgeofthecolumn (15).Turnbuckleshave
of 1 to 2 days. been used to tension the wires.
6.1.3 The column shall have ports at different heights to
5.5 A full investigation has not been conducted regarding
permitaccessforauxiliaryinstrumentationusedtomeasurethe
the correlation between HCFs obtained using the laboratory
volumetric water content and matric suction in the soil speci-
methods presented herein and HCFs of in-place materials.
men. The column shall have at least one port within 10 mm of
Thus, results obtained from the test methods should be applied
the soil surface and within 5 mm of the bottom of the soil
to field situations with caution and by qualified personnel.
specimen.Atleastthreeadditionalportsshallbespacedevenly
NOTE1—Thequalityoftheresultproducedbythisstandarddependson
the competence of the personnel performing the test and the suitability of between these upper and lower ports.
the equipment and facilities used. Agencies that meet the criteria of
6.1.4 Aminimumcolumndiameterof200mmshallbeused
Practice D3740 are generally considered capable of competent and
to capture the effects of preferential flow paths for water flow
objective testing, sampling, inspection, etc. Users of this standard are
thatarepresentinunsaturatedsoilsbecauseofcompactionand
cautioned that compliance with Practice D3740 does not in itself ensure
macro-features(micro-cracks,networksoflargepores).Alarge
reliable results. Reliable results depend on many factors. Practice D3740
provides a means of evaluating some of these factors.
diameter also helps to minimize boundary effects (side-wall
leakage) on flow through the soil specimen.
6. Apparatus
6.1.5 Theheightofthesoilspecimenmayhaveimplications
6.1 Column Apparatus (Category A):
onthetestingtimerequiredtoestablishwaterflowthroughthe
6.1.1 This apparatus is used to confine the soil specimen
soil specimen. The distribution of volumetric water content
during flow processes imposed in MethodsA1 throughA4.An
with height in the soil specimen can be influenced by the
example column apparatus is shown in Fig. 2.
outflow boundary for infiltration rates less than the saturated
hydraulic conductivity of the soil. Accordingly, the height of
the column should be large enough that there is a zone of soil
that is not influenced by the boundary.Acolumn height of 0.5
m may be used for coarse-grained soils, while a column height
greater than 1 m may be used for fine-grained soils (15). Other
column heights may be used if otherwise specified by the
requestor.The required column height may also be determined
for a specific test soil using the approach provided in (16).
However, the approach of (16) requires an estimate of the
SWRC and HCF for the soil.
NOTE2—Theheightofthecolumnshallbelargeenoughthattheupper
zone of the soil layer has a uniform distribution of volumetric water
content and matric suction with height during steady-state infiltration.
When the matric suction does not change with height, the total hydraulic
head is equal to the elevation head. In this case, the hydraulic gradient is
equal to one, a condition referred to as flow under a unit hydraulic
gradient. A sufficient column height is needed because the bottom
boundary of the column will typically have impedance to water flow
different from that of the soil, which will lead to the occurrence of a
capillarybreak.Thiswillpreventwaterfrompassingfromthesoilthrough
the bottom boundary until the soil is nearly water-saturated. This means
thatthevolumetricwatercontentandsuctionprofilesinthesoilspecimen
will change in the vicinity of the boundary, complicating interpretation of
results.
6.1.6 Infiltration Control System (Method A1):
6.1.6.1 This apparatus is used to control the rate of infiltra-
tion in the infiltration column test.
6.1.6.2 A peristaltic or infusion water pump, shown in Fig.
FIG. 2 Typical Column Test Setup (15) 3(a), shall be used to supply the constant inflow rate to the
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FIG. 3 Infiltration Control System: (a) Peristaltic Pump; (b) Fluid Distribution System
upper surface of the soil specimen. Peristaltic pump tubing piece of filter paper, shown in Fig. 5(a), has been used
shall be refreshed at least every 3 weeks to prevent changes in successfully in column tests on silts (15). The filter material
theflowrateduetocompressionofthetubingduringoperation shall be selected to have a porosity similar to the test soil.
of the peristaltic pump. The height of water in a graduated
6.1.8.3 Thecolumnshallbesealedtothepermeablesupport
cylinder connected to the inlet of the pump shall be monitored
plate to prevent leakage from the base of the column. An
as a backup to the pump velocity setting.
“O”-ring may be placed within a groove in the base of the
6.1.6.3 DuetothelowflowratesusedinHCFmeasurement,
column to provide a hydraulic seal with the porous plate, as
a system for distributing the infiltration evenly across the
shown in Fig. 5( b).
surface of the soil specimen shall be used. A successful
6.1.9 Outflow Measurement Systems (Category A):
approachusedinpracticeinvolvesplacingtheinflowlinefrom
6.1.9.1 For MethodA1, a tipping bucket [Fig. 6(a)] may be
the peristaltic pump into a small cup at the center of the soil
used to provide an electronic record of the volume of water
area, from which a series of cotton fiber wicks can be draped
collected from the base of the column. The funnel of the
across the soil surface, as shown in Fig. 3(b).
tipping bucket shall be placed beneath the permeable support
6.1.7 Evaporation Control System (Method A4):
plate so that it captures all water exiting from the base of the
6.1.7.1 This apparatus is used to control the infiltration rate
column. A graduated cylinder may also be used to provide a
in the evaporation column test.
back-up measurement of the water that passes out of the
6.1.7.2 A means of applying a constant relative humidity
tipping bucket [Fig. 6(b)].
andtemperaturetothesoilsurfaceshallbeusedinMethodA4.
6.1.9.2 For Methods A2, A3, and A4, a manometer system
An example of such a setup is shown in Fig. 4. An infrared
shall be used to control water flow from the bottom of the soil
lampmaybeusedtoprovideaconstanttemperaturetothesoil
specimen. Specifically, a water-filled manometer tube is useful
surface, and an electric fan may be used to provide air
to measure outflow during downward gravity drainage, to
circulation to the soil surface. If this approach is followed, a
provide a source of water imbibition from the base, or to help
layer of insulation shall be used to prevent heating of the
initially saturate the soil specimen for a surface evaporation
column sides.
test. In general, the manometer system may be used to impose
6.1.8 Base Support System (Category A):
water table at any height in the soil specimen. However, in
6.1.8.1 The base of the column shall rest on a permeable
order to measure the volume of water flow from or into the
supportplate,madefrommetaloracrylic.Thepurposesofthis
baseofthesoilspecimen,aMariottebottlemustbeattachedto
plate are to permit water drainage from the base of the soil
maintainaconstanthead.Anexamplesealingapproachforthe
specimen and to support the weight of the soil specimen.
manometer control system to the column and permeable
6.1.8.2 The permeable support plate shall serve as a freely-
support plate is shown in Fig. 6(c). The manometer tube shall
draining lower boundary to the soil specimen, having similar
also be fitted with valves that can be used to stop water flow
hydraulic impedance to the overlying soil in order to prevent
into or out of the base of the column.
the occurrence of a capillary break and prevent loss of soil
6.2 Axis Translation Apparatus (Category B):
particles. A honey-comb pattern of 2 mm holes overlain by a
6.2.1 Thistestsetupisusedformeasurementofthehydrau-
lic conductivity of unsaturated soils using the axis translation
technique.Apressure chamber (Method B1) or a flexible wall
permeameter (Method B2) may be included in this setup.
6.2.2 Regulated Pressure and Water Supply Source (Pres-
sure Panel) (Category B):
6.2.2.1 A regulated pressure source (an air compressor or
bottledgas)shallbeusedtosupplygaspressuresupto700kPa
(100 psi).
6.2.2.2 The pressure source and associated regulators shall
be capable of maintaining the desired pressure with an accu-
FIG. 4 Heat Lamp and Fan for Evaporation Column Test racy of 0.25% or better.
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FIG. 5 Column Test Base: (a) Base Support System; (b) Hydraulic Sealing System
FIG. 6 Outflow Monitoring Systems: (a) Tipping Bucket (Inside); (b) Tipping Bucket (Outside) with Graduated Cylinder; (c) Manometer
Outflow System
6.2.2.3 The pressure source shall be connected to graduated 6.2.3.2 The accuracy of the measuring device shall be
burettes, which can be filled with either water or air. The within 0.25% of the water or air pressure being applied.
graduationsontheburettesshallbesufficienttomeasurewater 6.2.4 Vacuum Pump and De-Airing Reservoir (Category B):
volumes of at least 1 mL, and shall have a volume of at least 6.2.4.1 Avacuumpumpcapableofapplyingavacuumofat
25 mL. least –80 kPa (–12 psi) shall be used to de-air water contained
6.2.2.4 The pressure source shall use incompressible tubing within a closed de-airing reservoir. A valve shall be included
(withastiffnessequalorgreaterthanHDPEplastic)toconnect suchthatthede-airingreservoirmaybeusedtofilltheburettes
the bottom of the burettes to the cell or bottom of the pressure in the pressure panel, or to apply vacuum directly to the
chamber or to the cell, top, and bottom of the flexible-wall pressure chamber or flexible wall permeameter.
permeameter. 6.2.5 Porous Disc or Membrane (Category B):
6.2.3 Pressure Indicators (Category B): 6.2.5.1 A porous disc shall be to provide a water-saturated
6.2.3.1 Bourdon gages or pressure transducers shall be used interfacebetweentheporewaterinthesoilandthewaterinthe
to measure the water and air pressures applied to the soil volume measuring system. When the porous disc is water-
specimenconfinedwithinthepressurechamberorflexiblewall saturated, air cannot pass through the disc. Porous discs shall
permeameter in the axis translation test. be fabricated from material that is hydrophilic and has an
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air-entry pressure greater than the maximum matric suction to confiningcollar.Formoreinformationonpossibledesignsofa
be applied during the test. Porous ceramic is the most com- pressure chamber, see (17).
monly used material. 6.2.12 The pressure chamber shall have a method of flush-
6.2.5.2 A cellulose membrane may also be used in the ing water beneath the bottom of the porous disc to remove air
flexible wall permeameter approach to provide a lower imped- bubbles, as shown in Fig. 8(b). An approach may involve a
ance to water flow due to their smaller thickness. Cellulose single,straightgrooveinthebottomplatenwhichconnectstwo
membranes shall not be used in the pressure chamber because water supply ports, or a network of grooves connected to the
of difficulties in sealing. two water supply ports (17).
6.2.6 Pressure Chamber (Method B1): 6.2.13 Flexible Wall Permeameter (Method B2):
6.2.6.1 A pressure chamber, such as that shown in Fig. 7, 6.2.13.1 The axis translation technique can also be incorpo-
may be used in axis-translation testing to apply a gas pressure rated into a flexible wall permeameter. In this approach, a
(typically air pressure) to a specimen resting on a water- cylindrical soil specimen is placed within a triaxial cell in
saturated, high-air entry porous disc (as specified in 6.2.4.1). whichthebottomporousstoneisreplacedwithahigh-airentry
6.2.7 The pressure chamber shall be a metallic vessel that porous disc or membrane. A schematic of the flexible-wall
shall be pressure-rated, at the very least, for 3 times the permeameter system for unsaturated soils is shown in Fig. 9.
maximum pressure to be applied to the vessel during the test. The flexible wall permeameter has the advantage over the
6.2.8 In some cases, the effects of overburden pressure may pressure chamber in that back-pressure saturation combined
besimulatedforatest.Forthesecases,thepressurevesselmay with measurement of Skempton’s B parameter (B = ∆u /∆σ)
w
be equipped with a piston and dial gauge for height measure- can be used to infer if the soil specimen is initially water-
ment during testing. A coarse porous confining mass that saturated or not. The flexible wall permeameter also has the
permits free flow of air shall be placed above the specimen. advantage that specimens may either be remolded specimens
6.2.9 The pressure chamber shall have a sealed, non- extruded from a compaction mold or undisturbed samples
collapsing outflow tube that connects the atmospheric pressure extruded from a field sampling tube.
side of the porous plate (or membrane) to the outside of the 6.2.13.2 The specimen in the flexible wall permeameter
pressure chamber. Schematics and photographs of an example shall have a diameter which is 1 to 2 cm less than the high
pressure chamber are shown in Fig. 7(a) and Fig. 7(b), air-entry porous disc. This contrast in diameter permits the
respectively. latex membrane to overlap the sides and part of the upper
6.2.10 The soil specimen shall be contained within a retain- surface of the porous disc as shown in Fig. 9. This overlap
ing ring, which may have similar dimensions to a standard prevents air from passing around the edge of the porous disc.
oedometer test ring (inside diameter of 6.35 cm, height of 2.54 Alternatively,theporousdiscmaybeaffixedtoarecesswithin
cm). This height is suitable to balance the uncertainty due to the bottom platen using epoxy suitable for porous materials
the difference in matric suction across the thickness of the according to the porous ceramic disc manufacturer specifica-
specimen during testing, with the need to have sufficient water tions.
storage in the specimen to provide measurable outflow values 6.2.13.3 A cellulose porous membrane having a high air-
during testing. entry suction may also be used in the flexible-wall permeame-
6.2.11 The pressure chamber shall have a means of provid- ter. Cellulose membranes have less of an impact on the
ingahydraulicsealaroundtheporousceramicdisc,inorderto hydraulic gradient than ceramic porous discs due to their
prevent air or water from passing around the edges of the disc. smaller thickness, so they may be desirable when testing soils
Asquare “O”-ring is used in the detailed drawing in Fig. 8(a) with higher permeability. They may be used in a flexible wall
and Fig. 8(b), which provides a seal between the edges of the permeameter without any special modification. Specifically, if
porousdiscandthebottomofthespecimenretainingringwhen the specimen has a diameter that is 1 to 2 cm less than the
the retaining ring is compressed onto the “O”-ring with the celluloseporousmembrane,thelatexmembranewillprovidea
FIG. 7 Pressure Chamber Setup: (a) Schematic; (b) Picture of Disassembled Setup
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FIG. 8 Pressure Chamber Setup: (a) Expanded Cross-Section; (b) Base Detail
FIG. 9 Flexible Wall Permeameter for Unsaturated Soils Testing
hydraulic seal between the bottom platen of the permeameter 6.3 Centrifuge Permeameter Apparatus (Category C):
and the cellulose membrane (see Fig. 9).
6.3.1 Centrifuge (Category C):
6.2.13.4 Volume changes during de-saturation of a speci-
6.3.1.1 The centrifuge used for this method may either be a
men may be evaluated using a force-displacement system
geotechnical centrifuge or a medical centrifuge in which the
involvingapistonconnectedtothetopofthespecimen,loaded
angular velocity w can be controlled by the test user.
with a pressure equivalent to the hydrostatic pressure in the
NOTE 3—Geotechnical centrifuges typically have an outside diameter
permeameter.
greater than 2 m, and can spin soil specimens weighing 1 kg or greater at
6.2.13.5 The flexible-wall permeameter shall be equipped
ω>875RPM.Geotechnicalcentrifugesareoftenequippedwithon-board
with flushing lines for air and water in the top and bottom
data acquisition systems which can be used to collect data from sensors
platens, respectively. duringcentrifugation.Medicalcentrifugestypicallyhaveasmalleroutside
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diameter of up to 0.5 m, and can spin soil specimens weighing less than
viewsofanexamplecentrifugepermeameterareshowninFig.
100gat ω > 3000 RPM. Medical centrifuges do not have on-board data
11(a) and Fig. 11(b), respectively.
acquisition systems so measurements of the flow process cannot be made
6.3.3.2 The component of the centrifuge permeameter that
duringcentrifugation.Althoughtheuseofmedicalcentrifugestomeasure
holds the soil specimen shall be a rigid-wall cylinder (that is,
the hydraulic conductivity of unsaturated soils is described by Test
Method D6527, this method compliments this standard by extending it to the permeameter). The permeameter shall be constructed of
centrifuges in general.
acrylic or another material that is not electrically conductive.
6.3.3.3 The permeameter may have ports for instrumenta-
6.3.1.2 The centrifuge shall be thermostatically controlled,
tion (see auxiliary equipment in section 6.4), and the outflow
capable of maintaining a temperature of 20°C.
reservoir may be equipped with a pressure transducer suitable
6.3.1.3 The centrifuge shall have a rotary union which is
for measuring the pressure at the bottom of a water column
capable of passing fluids from the stationary environment to
duringoutflow.Atleastoneoftheseportsshallbeintheupper
the spinning environment without pressurizing the water.
30% of the soil specimen height. The instrumentation may be
6.3.1.4 The centrifuge shall have a means of supporting the
embedded horizontally or vertically in the walls of the
permeameter system. A schematic view of the centrifuge
permeameter, as shown in the permeameter in Fig. 11(a) and
permeameterorientationduringcentrifugationisshowninFig.
10(a). The permeameter may be mounted horizontally, or can Fig. 11(b), or it may be embedded within the soil specimen.
Caution should be used when instrumentation is embedded
be supported using a swinging-basket system. A schematic of
an example swinging-basket is shown in Fig. 10(b). within the soil specimen to avoid settlement of the soil under
the increase weight of the instrument during centrifugation.
6.3.2 Flow Pump (Category C):
6.3.2.1 A flow pump capable of supplying flow rates from Any settlement observed as a result of embedded instrumen-
tation shall be reported.
0.1 to 1000 mL/h shall be used to supply fluid to the rotary
union of the centrifuge. 6.3.3.4 The component of the centrifuge permeameter used
tosupplywatertothetopofthesoilspecimen(thatis,thefluid
6.3.3 Centrifuge Permeameter Setup (Category C):
6.3.3.1 Thecentrifugepermeameteristhesystemwithinthe distributioncap)shallbeplacedatopthesoilspecimencylinder
as shown in Fig. 11(a). The fluid distribution cap shall
centrifuge that is used to hold the soil specimen, supply
infiltrationtothesurfaceofthesoilspecimen,andcollectwater connected using rigid tubing to the rotary union of the
centrifuge.
from the bottom of the soil specimen. Definitions of relevant
geometry variables for centrifuge permeameters are shown in 6.3.3.5 The component of the centrifuge permeameter used
Fig. 10( a) and Fig. 10(b). The value r is defined as radial to collect water from the bottom of the specimen (that is, the
distancefromthecentralaxisofthecentrifugetothebottomof outflow reservoir) shall be placed beneath the soil specimen
the soil specimen having length L. Isometric and cross-section cylinder. The outflow reservoir may rest atop the swinging
FIG. 10 Example Centrifuge Permeameter Setup (7): (a) Centrifuge Permeameter Orientation; (b) Example of Permeameter Support in a
Geotechnical Centrifuge
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FIG. 11 Schematic of a Centrifuge Permeameter (7): (a) Isometric View with Detail of Swinging Bucket Support System; (b) Cross-
Section View
basket of the centrifuge, or it can be integrated into the porousdisc,waterwillflowacrosstheinterfaceuntilthewater
swingingbasketofthecentrifugeitself,asshowninFig.11(a). pressure within the reservoir is the same as the suction within
The centrifuge shall include a measurement
...