1、Designation: D 7300 06Standard Test Method forLaboratory Determination of Strength Properties of FrozenSoil at a Constant Rate of Strain1This standard is issued under the fixed designation D 7300; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONKnowledge of the stress-strain-strength behavior of frozen soil is of great importance for
3、civilengineering construction in permafrost regions. The behavior of frozen soils under load is usually verydifferent from that of unfrozen soils because of the presence of ice and unfrozen water films. Inparticular, frozen soils are much more subject to creep and relaxation effects, and their behav
4、ior isstrongly affected by temperature change. In addition to creep, volumetric consolidation may alsodevelop in frozen soils having large unfrozen water or gas contents.As with unfrozen soil, the deformation and strength behavior of frozen soils depends on interparticlefriction, particle interlocki
5、ng, and cohesion. In frozen soil, however, bonding of particles by ice maybe the dominant strength factor. The strength of ice in frozen soil is dependent on many factors, suchas temperature, pressure, strain rate, grain size, crystal orientation, and density. At very high icecontents (ice-rich soil
6、s), frozen soil behavior under load is similar to that of ice. In fact, forfine-grained soils, experimental data suggest that the ice matrix dominates when mineral volumefraction is less than about 50 %. At low ice contents, however, (ice-poor soils), when interparticleforces begin to contribute to
7、strength, the unfrozen water films play an important role, especially infine-grained soils. Finally, for frozen sand, maximum strength is attained at full ice saturation andmaximum dry density (1).21. Scope1.1 This test method covers the determination of thestrength behavior of cylindrical specimens
8、 of frozen soil,subjected to uniaxial compression under controlled rates ofstrain. It specifies the apparatus, instrumentation, and proce-dures for determining the stress-strain-time, or strength versusstrain rate relationships for frozen soils under deviatoric creepconditions.1.2 Values stated in S
9、I units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulator
10、y limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 653 Terminology Relating to Soil, Rock, and ContainedFluids3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 creep of frozen groundthe irrecoverable time-dependent deviatoric deformation that results from lo
11、ng-termapplication of a deviatoric stress.3.1.2 excess icethe volume of ice in the ground whichexceeds the total pore volume that the ground would haveunder unfrozen conditions.3.1.3 failurethe stress condition at failure for a testspecimen. Failure is often taken to correspond to the maximumprincip
12、al stress difference (maximum deviator stress) attained,or the principal stress difference (deviator stress) at 15 % axial1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.19 on Frozen Soils andRock.Current edition a
13、pproved Nov. 1, 2006. Published January 2007.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volu
14、me information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.strain, whichever is obtained first during the performance of atest. Depending on frozen soil behavior an
15、d field application,other suitable failure criteria may be defined, such as theprincipal stress difference (deviator stress) at a selected axialstrain or strain rate.3.1.4 ground icea general term referring to all types of iceformed in freezing or frozen ground.3.1.5 ice-bearing permafrostpermafrost
16、 that contains ice.3.1.6 ice-bonded permafrostice-bearing permafrost inwhich the soil particles are cemented together by ice.3.1.7 ice contentthe ratio of the mass of ice contained inthe pore spaces of frozen soil or rock material, to the mass ofsolid particles in that material, expressed as percent
17、age.3.1.8 ice lensa dominant horizontal, lens-shaped body ofice of any dimension.3.1.9 ice-rich permafrostpermafrost containing excessice.3.1.10 permafrostsoil or rock that remains frozen (tem-perature 0C) for a period of two or more years.3.1.11 pore iceice occurring in the pores of soil and rocks.
18、3.1.12 samplepiece or quantity of bulk material that hasbeen selected by some sampling process.3.1.13 specimenpieces or quantity taken or prepared froma sample for testing.3.1.14 total water contentthe ratio of the mass of water(unfrozen water + ice) contained in the pore spaces of frozensoil or roc
19、k material, to the mass of solid particles in thatmaterial, expressed as percentage.3.1.15 unfrozen water contentthe ratio of the mass ofwater (free and adsorbed) contained in the pore spaces offrozen soil or rock material, to the mass of solid particles inthat material, expressed as percentage (2).
20、3.2 For definitions of other terms used in this test method,refer to Terminology D 653.4. Summary of Test Method4.1 A cylindrical frozen soil specimen is cut to length andthe ends are machined flat. The specimen is placed in a loadingchamber and allowed to stabilize at a desired test temperature.Ast
21、rain rate in compression is applied to the specimen and heldconstant at the specified temperature for the duration of thetest. Axial stress and deformation of the specimen are moni-tored continuously. Typical results of a set of uniaxial com-pression tests are shown in Fig. X1.1 (3).5. Significance
22、and Use5.1 Understanding the mechanical properties of frozen soilsis of primary importance to frozen ground engineering. Datafrom strain rate controlled compression tests are necessary forthe design of most foundation elements embedded in, orbearing on frozen ground. They make it possible to predict
23、 thetime-dependent settlements of piles and shallow foundationsunder service loads, and to estimate their short and long-termbearing capacity. Such tests also provide quantitative param-eters for the stability analysis of underground structures thatare created for permanent or semi-permanent use.5.2
24、 It must be recognized that the structure of frozen soil insitu and its behavior under load may differ significantly fromthat of an artificially prepared specimen in the laboratory. Thisis mainly due to the fact that natural permafrost ground maycontain ice in many different forms and sizes, in addi
25、tion to thepore ice contained in a small laboratory specimen. These largeground-ice inclusions (such as ice lenses) will considerablyaffect the time-dependent behavior of full-scale engineeringstructures.5.3 In order to obtain reliable results, high-quality undis-turbed representative permafrost sam
26、ples are required forcompression strength tests. The quality of the sample dependson the type of frozen soil sampled, the in situ thermal conditionat the time of sampling, the sampling method, and thetransportation and storage procedures prior to testing. The besttesting program can be ruined by poo
27、r-quality samples. Inaddition, one must always keep in mind that the application oflaboratory results to practical problems requires much cautionand engineering judgment.6. Apparatus6.1 Axial Loading DeviceThe axial compression deviceshall be capable of maintaining a constant strain rate within onep
28、ercent of the applied strain rate. The device may be a screwjack driven by an electric motor through a geared transmission,a platform weighing scale equipped with a screw-jack-activated load yoke, a deadweight load apparatus, a hydraulicor pneumatic loading device, or any other compression devicewit
29、h sufficient capacity and control to provide the loadingconditions prescribed in Section 8. Vibrations due to theoperation of the loading device should be kept at a minimum.6.2 Axial Load-Measuring DeviceThe axial load-measuring device may be a load ring, electronic load cell,hydraulic load cell, or
30、 any other load measuring device capableof the accuracy prescribed in this paragraph and may be a partof the axial loading device. For frozen soil with a deviatorstress at failure of less than 100 kPa, the axial load measuringdevice shall be capable of measuring the unit axial load to anaccuracy equ
31、ivalent to 1 kPa; for frozen soil with a deviatorstress at failure of 100 kPa and greater, the axial load-measuring device shall be capable of measuring the axial loadto an accuracy of 1 % of the axial load at failure.6.3 Measurement of Axial DeformationThe interactionbetween the test specimen and t
32、he testing machine loadingsystem can affect the test results. For this reason, in order toobserve the true stress-strain-rate behavior of a frozen soilspecimen, deformations should be measured directly on thespecimen. This can be achieved by mounting deformationgages on special holders attached to t
33、he sides of the specimen(4). If deformations are measured between the loading platens,it should be recognized that some initial deformation (seatingerror) will occur between the specimen ends and the loadingsurface of the platens.6.4 Bearing SurfacesThe specimen cap and base shall beconstructed of a
34、 noncorrosive impermeable material, and eachshall have a circular plane surface of contact with the specimenand a circular cross section. The weight of the specimen capshall be less than 0.5 % of the applied axial load at failure. Thediameter of the cap and base shall be greater than the diameterof
35、the specimen. The stiffness of the end cap should normallybe high enough to distribute the applied load uniformly overthe loading surface of the specimen. The specimen base shallD7300062be coupled to the compression chamber so as to prevent lateralmotion or tilting, and the specimen cap shall be des
36、igned toreceive the piston, such that the piston-to-cap contact area isconcentric with the cap.NOTE 1It is advisable not to use ball or spherical seats that wouldallow rotation of the platens, but rather special care should be taken intrimming or molding the ends of the specimen to parallel planes.
37、The endsof the specimen shall be flat to 0.02 mm and shall not depart fromperpendicularity to the axis of the specimen by more than 0.001 radian(about 3.5 min) or 0.05 mm in 50 mm. Effects of end friction on specimendeformation can be tolerated if the height to diameter ratio of the testspecimen is
38、two to three. However, it is recommended that lubricatedplatens be used whenever possible in the uniaxial compression and creeptesting of frozen soils. The lubricated platen should consist of a circularsheet of 0.8-mm thick latex membrane, attached to the loading face of asteel platen with a 0.5-mm
39、thick layer of high-vacuum silicone grease. Thesteel platens are polished stainless steel disks about 10 mm larger than thespecimen diameter. As the latex sheets and grease layers compress underload, the axial strain of the specimen should be measured using exten-someters located on the specimen (5,
40、 6).6.5 Thermal ControlThe compressive strength of frozensoil is also affected greatly by temperature and its fluctuations.It is imperative, therefore, that specimens be stored and testedin a freezing chamber that has only a small temperaturefluctuation to minimize thermal disturbance. Reduce the ef
41、fectof fluctuations in temperature by enclosing the specimen in aninsulating jacket during storage and testing. Reference (7)suggests the following permissible temperature variationswhen storing and testing frozen soils within the followingdifferent ranges:Temperature, C 0 to 2 2 to 5 5 to 10 below
42、10Permissible deviation, C 60.1 60.2 60.5 61.07. Test Specimen7.1 Thermal Disturbance Effects:7.1.1 The strength and deformation properties of frozen soilsamples are known to be affected by sublimation, evaporation,and thermal disturbance. Their effect is in the redistribution andultimate loss of mo
43、isture from the sample as the result of atemperature gradient or low-humidity environment, or both.Loss of moisture reduces the cohesion between soil particlesand may reduce the strength (that is dependent on tempera-ture). The effects of moisture redistribution in frozen soil arethought to change i
44、ts strength and creep behavior.7.1.2 Thermal disturbance of a frozen sample refers not onlyto thawing, but also to temperature fluctuations. Soil structuremay be changed completely if the sample is thawed and thenrefrozen. Temperature fluctuations can set up thermal gradi-ents, causing moisture redi
45、stribution and possible change in theunfrozen moisture content. Take care, therefore, to ensure thatfrozen soil specimens remain in their natural state, and thatthey are protected against the detrimental effects of sublimationand thermal disturbance until testing is completed.7.1.3 In the event that
46、 the soil sample is not maintained atthe in situ temperature prior to testing, bring the test specimento the test temperature from a higher temperature to reduce thehysteresis effect on the unfrozen water content.7.1.4 Before testing, maintain the test specimen at the testtemperature for a sufficien
47、t period, to ensure that the tempera-ture is uniform throughout the volume.7.2 Machining and Preparation of Specimens for Testing(7):7.2.1 The machining and preparation procedures used forfrozen soils depend upon the size and shape of the specimenrequired, the type of soil, and the particular test b
48、eing per-formed. Follow similar procedures for cutting and machiningboth naturally frozen and artificially frozen samples.7.2.2 Handle frozen soil samples with gloves and all toolsand equipment kept in the cold room to avoid sample damageby localized thawing. A temperature of 5 6 1C is the mostsuita
49、ble ambient temperature for machining with respect tomaterial workability and personal comfort. At warmer tem-peratures, surface thawing is a problem, and cutting tools mustbe cleaned frequently, for they become coated and cloggedwith frozen soil, reducing their cutting efficiency. Working atcolder temperatures is uncomfortable and slow. The soil is alsodifficult to work with because of increased hardness; cracksmay also be formed easily in it, due to increased brittleness.7.2.3 After being cut roughly to the required dimension,rectangular specimens are f
