ASTM D5520-94(2006)e1
(Test Method)Standard Test Method for Laboratory Determination of Creep Properties of Frozen Soil Samples by Uniaxial Compression
Standard Test Method for Laboratory Determination of Creep Properties of Frozen Soil Samples by Uniaxial Compression
SIGNIFICANCE AND USE
Understanding the mechanical properties of frozen soils is of primary importance to permafrost engineering. Data from creep tests are necessary for the design of most foundation elements embedded in, or bearing on frozen ground. They make it possible to predict the time-dependent settlements of piles and shallow foundations under service loads, and to estimate their short- and long-term bearing capacity. Creep tests also provide quantitative parameters for the stability analysis of underground structures that are created for permanent use.
It must be recognized that the structure of frozen soil in situ and its behavior under load may differ significantly from that of an artificially prepared specimen in the laboratory. This is mainly due to the fact that natural permafrost ground may contain ice in many different forms and sizes, in addition to the pore ice contained in a small laboratory specimen. These large ground-ice inclusions (such as ice lenses) will considerably affect the time-dependent behavior of full-scale engineering structures.
In order to obtain reliable results, high-quality undisturbed representative permafrost samples are required for creep tests. The quality of the sample depends on the type of frozen soil sampled, the in situ thermal condition at the time of sampling, the sampling method, and the transportation and storage procedures prior to testing. The best testing program can be ruined by poor-quality samples. In addition, one must always keep in mind that the application of laboratory results to practical problems requires much caution and engineering judgment.
SCOPE
1.1 This test method covers the determination of the creep behavior of cylindrical specimens of frozen soil, subjected to uniaxial compression. It specifies the apparatus, instrumentation, and procedures for determining the stress-strain-time, or strength versus strain rate relationships for frozen soils under deviatoric creep conditions.
1.2 Although this test method is one that is most commonly used, it is recognized that creep properties of frozen soil related to certain specific applications, can also be obtained by some alternative procedures, such as stress-relaxation tests, simple shear tests, and beam flexure tests. Creep testing under triaxial test conditions will be covered in another standard.
1.3 Values stated in SI units are to be regarded as the standard.
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:D5520–94 (Reapproved 2006)
Standard Test Method for
Laboratory Determination of Creep Properties of Frozen Soil
Samples by Uniaxial Compression
This standard is issued under the fixed designation D5520; 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.
´ NOTE—Editorial changes were made in June 2006.
INTRODUCTION
Knowledge of the stress-strain-strength behavior of frozen soil is of great importance for civil
engineeringconstructioninpermafrostregions.Thebehavioroffrozensoilsunderloadisusuallyvery
different from that of unfrozen soils because of the presence of ice and unfrozen water films. In
particular, frozen soils are much more subject to creep and relaxation effects, and their behavior is
strongly affected by temperature change. In addition to creep, volumetric consolidation may also
develop in frozen soils having large unfrozen water or gas contents.
Aswithunfrozensoil,thedeformationandstrengthbehavioroffrozensoilsdependsoninterparticle
friction, particle interlocking, and cohesion. In frozen soil, however, bonding of particles by ice may
be the dominant strength factor.The strength of ice in frozen soil is dependent on many factors, such
as temperature, pressure, strain rate, grain size, crystal orientation, and density. At very high ice
contents (ice-rich soils), frozen soil behavior under load is similar to that of ice. In fact, for
fine-grained soils, experimental data suggest that the ice matrix dominates when mineral volume
fraction is less than about 50%. At low ice contents, however, (ice-poor soils), when interparticle
forces begin to contribute to strength, the unfrozen water films play an important role, especially in
fine-grained soils. Finally, for frozen sand, maximum strength is attained at full ice saturation and
maximum dry density (1).
1. Scope 1.3 Values stated in SI units are to be regarded as the
standard.
1.1 This test method covers the determination of the creep
1.4 This standard does not purport to address all of the
behavior of cylindrical specimens of frozen soil, subjected to
safety concerns, if any, associated with its use. It is the
uniaxial compression. It specifies the apparatus, instrumenta-
responsibility of the user of this standard to establish appro-
tion, and procedures for determining the stress-strain-time, or
priate safety and health practices and determine the applica-
strength versus strain rate relationships for frozen soils under
bility of regulatory limitations prior to use.
deviatoric creep conditions.
1.2 Although this test method is one that is most commonly
2. Referenced Documents
used,itisrecognizedthatcreeppropertiesoffrozensoilrelated
2.1 ASTM Standards:
to certain specific applications, can also be obtained by some
D653 Terminology Relating to Soil, Rock, and Contained
alternative procedures, such as stress-relaxation tests, simple
Fluids
shear tests, and beam flexure tests. Creep testing under triaxial
D2850 Test Method for Unconsolidated-UndrainedTriaxial
test conditions will be covered in another standard.
Compression Test on Cohesive Soils
D4083 Practice for Description of Frozen Soils (Visual-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland Manual Procedure)
Rock and is the direct responsibility of Subcommittee D18.19 on Frozen Soils and
Rock.
Current edition approved May 1, 2006. Published June 2006. Originally
approved in 1994. Last previous edition approved in 2001 as D5520–94(2001). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/D5520-94R06E01. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
the text. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D5520–94 (2006)
D4341 Test Method for Creep of Hard Rock Core Speci- 5. Significance and Use
mens in Uniaxial Compression at Ambient or Elevated
5.1 Understanding the mechanical properties of frozen soils
Temperature
is of primary importance to permafrost engineering. Data from
D4405 TestMethodforCreepofSoftRockCoreSpecimens
creep tests are necessary for the design of most foundation
inUniaxialCompressionatAmbientorElevatedTempera-
elements embedded in, or bearing on frozen ground. They
ture
make it possible to predict the time-dependent settlements of
D4406 Test Method for Creep of Rock Core Specimens in
piles and shallow foundations under service loads, and to
Triaxial Compression at Ambient or Elevated Tempera-
estimate their short- and long-term bearing capacity. Creep
tures
tests also provide quantitative parameters for the stability
analysis of underground structures that are created for perma-
3. Terminology
nent use.
3.1 Definitions:
5.2 It must be recognized that the structure of frozen soil in
3.1.1 creep—of frozen ground, the irrecoverable time-
situ and its behavior under load may differ significantly from
dependent deviatoric deformation that results from long-term
that of an artificially prepared specimen in the laboratory.This
application of a deviatoric stress.
is mainly due to the fact that natural permafrost ground may
3.1.2 excess ice—the volume of ice in the ground which
containiceinmanydifferentformsandsizes,inadditiontothe
exceeds the total pore volume that the ground would have
pore ice contained in a small laboratory specimen.These large
under unfrozen conditions.
ground-ice inclusions (such as ice lenses) will considerably
3.1.3 ground ice—ageneraltermreferringtoalltypesofice
affect the time-dependent behavior of full-scale engineering
formed in freezing or frozen ground.
structures.
3.1.4 ice-bearing permafrost—permafrost that contains ice.
5.3 In order to obtain reliable results, high-quality undis-
3.1.5 ice-bonded permafrost—ice-bearing permafrost in
turbedrepresentativepermafrostsamplesarerequiredforcreep
which the soil particles are cemented together by ice.
tests. The quality of the sample depends on the type of frozen
3.1.6 ice content—the ratio of the mass of ice contained in
soil sampled, the in situ thermal condition at the time of
the pore spaces of frozen soil or rock material, to the mass of
sampling, the sampling method, and the transportation and
solid particles in that material, expressed as percentage.
storage procedures prior to testing. The best testing program
3.1.7 ice lens—a dominant horizontal, lens-shaped body of
can be ruined by poor-quality samples. In addition, one must
ice of any dimension.
always keep in mind that the application of laboratory results
3.1.8 ice-rich permafrost—permafrost containing excess
to practical problems requires much caution and engineering
ice.
judgment.
3.1.9 permafrost—perennially frozen soil or rock.
3.1.10 poreice—iceoccurringintheporesofsoilandrocks.
6. Apparatus
3.1.11 sample—a portion of a material intended to be
6.1 Axial Loading Device—The axial compression device
representative of the whole.
shallbecapableofmaintainingaconstantloadorstresswithin
3.1.12 specimen—a piece or portion of a sample used to
one percent of the applied load or stress. The device may be a
make a test.
screw jack driven by an electric motor through a geared
3.1.13 total water content—the ratio of the mass of water
transmission, a platform weighing scale equipped with a
(unfrozen water+ice) contained in the pore spaces of frozen
screw-jack-activatedloadyoke,adeadweightloadapparatus,a
soil or rock material, to the mass of solid particles in that
hydraulic or pneumatic loading device, or any other compres-
material, expressed as percentage.
sion device with sufficient capacity and control to provide the
3.1.14 unfrozen water content—the ratio of the mass of
loading conditions prescribed in Section 8. Vibrations due to
water (free and adsorbed) contained in the pore spaces of
the operation of the loading device should be kept at a
frozen soil or rock material, to the mass of solid particles in
minimum.
that material, expressed as percentage (2).
6.2 Axial Load-Measuring Device—The axial load-
3.2 For definitions of other terms used in this test method,
measuring device may be a load ring, electronic load cell,
refer to Terminology D653.
hydraulicloadcell,oranyotherloadmeasuringdevicecapable
4. Summary of Test Method
of the accuracy prescribed in this paragraph and may be a part
4.1 A cylindrical frozen soil specimen is cut to length and
of the axial loading device. For frozen soil with a deviator
theendsaremachinedflat.Thespecimenisplacedinaloading stress at failure of less than 100 kPa, the axial loadmeasuring
chamber and allowed to stabilize at a desired test temperature.
device shall be capable of measuring the unit axial load to an
Anaxialcompressionstressisappliedtothespecimenandheld accuracy equivalent to 1 kPa; for frozen soil with a deviator
constant at the specified temperature for the duration of the
stress at failure of 100 kPa and greater, the axial load-
test. Specimen deformation is monitored continuously.Typical measuring device shall be capable of measuring the axial load
results of a uniaxial compression creep test are shown in Fig.
to an accuracy of 1% of the axial load at failure.
X1.1.
6.3 Measurement of Axial Deformation—The interaction
between the test specimen and the testing machine loading
systemcanaffectthecreeptestresults.Forthisreason,inorder
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org. to observe the true strain-time behavior of a frozen soil
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D5520–94 (2006)
specimens, deformations should be measured directly on the 7.1.2 Thermaldisturbanceofafrozensamplerefersnotonly
specimen. This can be achieved by mounting deformation to thawing, but also to temperature fluctuations. Soil structure
gages on special holders attached to the sides of the specimen may be changed completely if the sample is thawed and then
(3). If deformations are measured between the loading platens, refrozen. Temperature fluctuations can set up thermal gradi-
it should be recognized that some initial deformation (seating ents,causingmoistureredistributionandpossiblechangeinthe
error) will occur between the specimen ends and the loading unfrozen moisture content. Take care, therefore, to ensure that
surface of the platens. frozen soil specimens remain in their natural state, and that
6.4 Bearing Surfaces—The specimen cap and base shall be theyareprotectedagainstthedetrimentaleffectsofsublimation
constructed of a noncorrosive impermeable material, and each and thermal disturbance until testing is completed.
shallhaveacircularplanesurfaceofcontactwiththespecimen
7.1.3 In the event that the soil sample is not maintained at
and a circular cross section. The weight of the specimen cap
the in situ temperature prior to testing, bring the test specimen
shallbelessthan0.5%oftheappliedaxialloadatfailure.The
to the test temperature from a higher temperature to reduce the
diameter of the cap and base shall be greater than the diameter
hysteresis effect on the unfrozen water content.
of the specimen. The stiffness of the end cap should normally
7.1.4 Before testing, maintain the test specimen at the test
be high enough to distribute the applied load uniformly over
temperature for a sufficient period, to ensure that the tempera-
the loading surface of the specimen. The specimen base shall
ture is uniform throughout the volume.
becoupledtothecompressionchambersoastopreventlateral
7.2 Machining and Preparation of Specimens for Testing:
motion or tilting, and the specimen cap shall be designed to
7.2.1 The machining and preparation procedures used for
receive the piston, such that the piston-to-cap contact area is
frozen soils depend upon the size and shape of the specimen
concentric with the cap.
required, the type of soil, and the particular test being per-
NOTE 1—It is advisable not to use ball or spherical seats that would
formed. Follow similar procedures for cutting and machining
allow rotation of the platens, but rather special care should be taken in
both naturally frozen and artificially frozen samples.
trimmingormoldingtheendsofthespecimentoparallelplanes.Theends
7.2.2 Handle frozen soil samples with gloves and all tools
of the specimen shall be flat to 0.02 mm and shall not depart from
and equipment kept in the cold room to avoid sample damage
perpendicularity to the axis of the specimen by more than 0.001 radian
(about3.5min)or0.05mmin50mm.Effectsofendfrictiononspecimen by localized thawing.Atemperature of−5 6 1°C is the most
deformation can be tolerated if the height to diameter ratio of the test
suitable ambient temperature for machining with respect to
specimen is two to three. However, it is recommended that lubricated
material workability and personal comfort.
platens be used whenever possible in the uniaxial compression and creep
7.2.3 Cylindrical specimens are either machined on a work-
testing of frozen soils. The lubricated platen should consist of a circular
ing lathe or cut carefully with a coring tube in the laboratory.
sheet of 0.8-mm thick latex membrane, attached to the loading face of a
steelplatenwitha0.5-mmthicklayerofhighvacuumsiliconegrease.The They can also be cored from block samples, using a diamond
steelplatensarepolishedstainlesssteeldisksabout10mmlargerthanthe
set core barrel and a large industrial drill press. For machining
specimen diameter.As the latex sheets and grease layers compress under
on a working lathe, the best results are obtained when the
load, the axial strain of the specimen should be measured using exten-
specimen is turned at 690 r/min and the carriage feed set at 30
someters located on the specimen (4, 5).
mm per 36 revolutions. Limit the maximum depth of cut to
6.5 Thermal Control—The compressive strength of frozen
0.38 mm. A tungsten carbide cutting tool, with a minimum
soil is also affected greatly by temperature and its fluctuations.
back clearance of 45°, gives the best results. For clean cuts,
It is imperative, therefore, that specimens be stored and tested
sharpen the tool often, as the abrasive action of the soil dulls
in a freezing chamber that has only a small temperature
the edge quickly (7). Shaping coarse sand or gravel specimens
fluctuation to minimize thermal disturbance. Reduce the effect
on a lathe is difficult, because the soil grains are pulled out
of fluctuations in temperature by enclosin
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