1、Designation: D 2850 03a (Reapproved 2007)Standard Test Method forUnconsolidated-Undrained Triaxial Compression Test onCohesive Soils1This standard is issued under the fixed designation D 2850; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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.1. Scope1.1 This test method covers determination of the strengthand stress-strain relationships of a cylin
3、drical specimen ofeither undisturbed or remolded cohesive soil. Specimens aresubjected to a confining fluid pressure in a triaxial chamber. Nodrainage of the specimen is permitted during the test. Thespecimen is sheared in compression without drainage at aconstant rate of axial deformation (strain c
4、ontrolled).1.2 This test method provides data for determining und-rained strength properties and stress-strain relations for soils.This test method provides for the measurement of the totalstresses applied to the specimen, that is, the stresses are notcorrected for pore-water pressure.NOTE 1The dete
5、rmination of the unconfined compressive strength ofcohesive soils is covered by Test Method D 2166.NOTE 2The determination of the consolidated, undrained strength ofcohesive soils with pore pressure measurement is covered by Test MethodD 4767.1.3 All observed and calculated values shall conform to t
6、heguidelines for significant digits and rounding established inPractice D 6026.1.3.1 The method used to specify how data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the
7、 results obtained using thisstandard is beyond its scope.1.4 The values stated in SI units are to be regarded as thestandard. The values stated in inch-pound units and given inparentheses are approximate.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with
8、 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 422 Test Method for Particle-Size Analysis of SoilsD 653 Terminolo
9、gy Relating to Soil, Rock, and ContainedFluidsD 854 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD 1587 Practice for Thin-Walled Tube Sampling of Soilsfor Geotechnical PurposesD 2166 Test Method for Unconfined Compressive Strengthof Cohesive SoilD 2216 Test Methods for Laborato
10、ry Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D 2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)D 3740 Practice for Minimum Requirements f
11、or AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and ConstructionD 4220 Practices for Preserving and Transporting SoilSamplesD 4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD 4753 Guide for Evaluating, Selecting, and S
12、pecifyingBalances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD 4767 Test Method for Consolidated Undrained TriaxialCompression Test for Cohesive SoilsD 6026 Practice for Using Significant Digits in Geotechni-cal Data3. Terminology3.1 DefinitionsThe definitions of ter
13、ms used in this testmethod shall be in accordance with Terminology D 653.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.05 on Strength andCompressibility of Soils
14、.Current edition approved Sept. 15, 2007. Published October 2007. Originallyapproved in 1970. Last previous edition approved in 2003 as D 2850 03a.2For referenced ASTM Standards, visit the ASTM website, www.astm.org, orcontact Customer Service at serviceastm.org. For Annual Book of ASTM Stan-dardsvo
15、lume information, refer to the standards Document Summary page on theASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1 failurethe stress condition at failure for a testspecimen. Failure is often taken to correspond t
16、o the maximumprincipal stress difference (deviator stress) attained or theprincipal stress difference (deviator stress) at 15 % axial strain,whichever is obtained first during the performance of a test.3.2.2 unconsolidated-undrained compressive strengththevalue of the principal stress difference (de
17、viator stress) atfailure.4. Significance and Use4.1 In this test method, the compressive strength of a soil isdetermined in terms of the total stress, therefore, the resultingstrength depends on the pressure developed in the pore fluidduring loading. In this test method, fluid flow is not permittedf
18、rom or into the soil specimen as the load is applied, thereforethe resulting pore pressure, and hence strength, differs fromthat developed in the case where drainage can occur.4.2 If the test specimens are 100 % saturated, consolidationcannot occur when the confining pressure is applied nor duringth
19、e shear portion of the test since drainage is not permitted.Therefore, if several specimens of the same material are tested,and if they are all at approximately the same water content andvoid ratio when they are tested, they will have approximatelythe same undrained shear strength. The Mohr failure
20、envelopewill usually be a horizontal straight line over the entire rangeof confining stresses applied to the specimens if the specimensare fully saturated.4.3 If the test specimens are partially saturated or com-pacted specimens, where the degree of saturation is less than100 %, consolidation may oc
21、cur when the confining pressure isapplied and during shear, even though drainage is not permit-ted. Therefore, if several partially saturated specimens of thesame material are tested at different confining stresses, theywill not have the same undrained shear strength. Thus, theMohr failure envelope
22、for unconsolidated undrained triaxialtests on partially saturated soils is usually curved.4.4 The unconsolidated undrained triaxial strength is appli-cable to situations where the loads are assumed to take place sorapidly that there is insufficient time for the induced pore-waterpressure to dissipat
23、e and for consolidation to occur during theloading period (that is, drainage does not occur).4.5 Compressive strengths determined using this proceduremay not apply in cases where the loading conditions in the fielddiffer significantly from those used in this test method.NOTE 3Notwithstanding the sta
24、tements on precision and bias con-tained in this test method: The precision of this test method is dependenton the competence of the personnel performing it and the suitability of theequipment and facilities used.Agencies which meet the criteria of PracticeD 3740 are generally considered capable of
25、competent testing. Users ofthis test method are cautioned that compliance with Practice D 3740 doesnot ensure reliable testing. Reliable testing depends on several factors;Practice D 3740 provides a means of evaluating some of those factors.5. Apparatus5.1 Axial Loading DeviceThe axial loading devic
26、e shallbe screw jack driven by an electric motor through a gearedtransmission, a hydraulic loading device, or any other com-pression device with sufficient capacity and control to providethe rate of loading prescribed in 7.5. The rate of advance of theloading device shall not deviate by more than 65
27、 % from theselected value. Vibrations due to the operation of the loadingdevice shall be sufficiently small to not cause dimensionalchanges in the specimen.NOTE 4A loading device may be said to provide sufficiently smallvibrations if there are no visible ripples in a glass of water placed on theload
28、ing platen when the device is operating at the speed at which the testis performed.5.2 Axial Load-Measuring DeviceThe axial load-measuring device shall be a load ring, electronic load cell,hydraulic load cell, or any other load-measuring device capableof measuring the axial load to an accuracy of 1
29、% of the axialload at failure and may be a part of the axial loading device.5.3 Triaxial Compression ChamberThe triaxial chambershall consist of a top plate and a baseplate separated by acylinder. The cylinder shall be constructed of any materialcapable of withstanding the applied pressure. It is de
30、sirable touse a transparent material or have a cylinder provided withviewing ports so the behavior of the specimen may beobserved.The top plate shall have a vent valve such that air canbe forced out of the chamber as it is filled. The base plate shallhave an inlet through which the pressure liquid i
31、s supplied tothe chamber.5.4 Axial Load PistonThe piston passing through the topof the chamber and its seal must be designed so the variationin axial load due to friction does not exceed 0.1 % of the axialload at failure as measured in 8.4.1.3 and so there is negligiblelateral bending of the piston
32、during loading.NOTE 5The use of two linear ball bushings to guide the piston isrecommended to minimize friction and maintain alignment.NOTE 6A minimum piston diameter of one sixth the specimendiameter has been used successfully in many laboratories to minimizelateral bending.5.5 Pressure Control Dev
33、iceThe chamber pressure con-trol device shall be capable of applying and controlling thechamber pressure to within 62 kPa (0.25 psi) for pressures lessthan 200 kPa (28 psi) and to within 61 % for pressures greaterthan 200 kPa (28 psi). This device may consist of a reservoirconnected to the triaxial
34、chamber and partially filled with thechamber fluid (usually water), with the upper part of thereservoir connected to a compressed gas supply; the gaspressure being controlled by a pressure regulator and measuredby a pressure gage, electronic pressure transducer, or any otherdevice capable of measuri
35、ng to the prescribed tolerance.However, a hydraulic system pressurized by deadweight actingon a piston or any other pressure-maintaining and measurementdevice capable of applying and controlling the chamber pres-sure to the tolerance prescribed in this section may be used.5.6 Specimen Cap and BaseAn
36、 impermeable rigid capand base shall be used to prevent drainage of the specimen.Thespecimen cap and base shall be constructed of a noncorrosiveimpermeable material, and each shall have a circular planesurface of contact with the specimen and a circular crosssection. The weight of the specimen cap s
37、hall produce an axialstress on the specimen of less than 1 kN/m2. The diameter ofthe cap and base shall be equal to the initial diameter of thespecimen. The specimen base shall be connected to the triaxialcompression chamber to prevent lateral motion or tilting andD 2850 03a (2007)2the specimen cap
38、shall be designed such that eccentricity of thepiston to cap contact relative to the vertical axis of thespecimen does not exceed 1.3 mm (0.05 in.). The end of thepiston and specimen cap contact area shall be designed so thattilting of the specimen cap during the test is minimal. Thecylindrical surf
39、ace of the specimen base and cap that contactsthe membrane to form a seal shall be smooth and free ofscratches.5.7 Deformation IndicatorThe vertical deformation of thespecimen shall be measured with an accuracy of at least 0.03 %of the specimen height. The deformation indicator shall have arange of
40、at least 20 % of the height of the specimen, and maybe a dial indicator, linear variable differential transformer(LVDT), extensiometer or other measuring device meeting therequirements for accuracy and range.5.8 Rubber MembraneThe rubber membrane used toencase the specimen shall provide reliable pro
41、tection againstleakage. Membranes shall be carefully inspected prior to use,and if any flaws or pinholes are evident, the membrane shall bediscarded. To offer minimum restraint to the specimen, theunstretched membrane diameter shall be between 90 and 95 %of that of the specimen. The membrane thickne
42、ss shall notexceed 1 % of the diameter of the specimen. The membraneshall be sealed to the specimen base and cap with rubberO-rings for which the unstressed inside diameter is between 75and 85 % of the diameter of the cap and base or by any methodthat will produce a positive seal.An equation for cor
43、recting theprincipal stress difference (deviator stress) for the effect of thestiffness of the membrane is given in 8.7.5.9 Sample ExtruderThe sample extruder shall be capableof extruding the soil core from the sampling tube in the samedirection of travel in which the sample entered the tube andwith
44、 minimum disturbance of the sample. If the soil core is notextruded vertically, care should be taken to avoid bendingstresses on the core due to gravity. Conditions at the time ofsample removal may dictate the direction of removal, but theprincipal concern is to keep the degree of disturbance minima
45、l.5.10 Specimen Size Measurement Devices Devices usedto measure the height and diameter of the specimen shall becapable of measuring the desired dimension to within 0.1 % ofits actual length and shall be constructed such that their use willnot disturb the specimen.NOTE 7Circumferential measuring tap
46、es are recommended over cali-pers for measuring the diameter.5.11 TimerA timing device indicating the elapsed testingtime to the nearest 1 s shall be used for establishing the rate ofstrain application prescribed in 7.5.5.12 BalancesA balance or scale conforming to the re-quirements of Specification
47、 D 4753 readable (with no estima-tion) to 0.1 % of the test mass, or better.5.13 Miscellaneous ApparatusSpecimen trimming andcarving tools including a wire saw, steel straightedge, miterbox and vertical trimming lathe, apparatus for preparingcompacted specimens, remolding apparatus, water contentcan
48、s, and data sheets shall be provided as required.6. Test Specimens6.1 Specimen SizeSpecimens shall be cylindrical andhave a minimum diameter of 3.3 cm (1.3 in.). The height-to-diameter ratio shall be between 2 and 2.5. The largest particlesize shall be smaller than one sixth the specimen diameter. I
49、f,after completion of a test, it is found based on visual observa-tion that oversize particles are present, indicate this informa-tion in the report of test data (see 9.2.12).NOTE 8If oversize particles are found in the specimen after testing, aparticle-size analysis may be performed in accordance with Test MethodD 422 to confirm the visual observation and the results provided with thetest report (see 9.2.4).6.2 Undisturbed SpecimensPrepare undisturbed speci-mens from large undisturbed samples or from samples securedin accordance with Practice D 1587 or othe
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