1、Designation: D2850 15Standard Test Method forUnconsolidated-Undrained Triaxial Compression Test onCohesive Soils1This standard is issued under the fixed designation D2850; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers determination of the strengthand stress-strain relationships of a cylindrical specimen ofeit
3、her intact, compacted, or remolded cohesive soil. Specimensare subjected to a confining fluid pressure in a triaxial chamber.No drainage of the specimen is permitted during the applica-tion of the confining fluid pressure or during the compressionphase of the test. The specimen is axially loaded at
4、a constantrate of axial deformation (strain controlled).1.2 This test method provides data for determiningundrained strength properties and stress-strain relations forsoils. This test method provides for the measurement of thetotal stresses applied to the specimen, that is, the stresses arenot corre
5、cted for pore-water pressure.NOTE 1The determination of the unconfined compressive strength ofcohesive soils is covered by Test Method D2166/D2166M.NOTE 2The determination of the consolidated, undrained strength ofcohesive soils with pore pressure measurement is covered by Test MethodD4767.1.3 All o
6、bserved and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.3.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as theindustry standard. In addition, they are representative
7、 of thesignificant digits that generally should be retained. The proce-dures used do not consider material variation, purpose forobtaining the data, special purpose studies, or any consider-ations for the users objectives; and it is common practice toincrease or reduce significant digits of reported
8、 data to becommensurate with these considerations. It is beyond the scopeof this standard to consider significant digits used in analysismethods for engineering design.1.4 UnitsThe values stated in SI units are to be regardedas the standard.The values given in parentheses are mathemati-cal conversio
9、ns to inch-pound units, which are provided forinformation only and are not considered standard. Reporting oftest results in units other than SI shall not be regarded asnonconformance with this test method.1.4.1 The converted inch-pound units use the gravitationalsystem of units. In this system, the
10、pound (lbf) represents a unitof force (weight), while the unit for mass is slugs. The slug unitis not given, unless dynamic (F = ma) calculations areinvolved.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user
11、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:2D422 Test Method for Particle-Size Analysis of SoilsD653 Terminology Relating to Soil, Rock, and ContainedFluidsD8
12、54 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD1587 Practice for Thin-Walled Tube Sampling of Soils forGeotechnical PurposesD2166/D2166M Test Method for Unconfined CompressiveStrength of Cohesive SoilD2216 Test Methods for Laboratory Determination of Water(Moisture) Content o
13、f Soil and Rock by MassD2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)D3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of
14、 Soil and Rock asUsed in Engineering Design and ConstructionD4220/D4220M Practices for Preserving and TransportingSoil Samples1This 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 Soi
15、ls.Current edition approved Nov. 15, 2015. Published December 2015. Originallyapproved in 1970. Last previous edition approved in 2007 as D2850 03a (2007).DOI: 10.1520/D2850-15.2For referenced ASTM Standards, visit the ASTM website, www.astm.org, orcontact Customer Service at serviceastm.org. For An
16、nual Book of ASTM Stan-dardsvolume information, refer to the standards Document Summary page on theASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D4318 Tes
17、t Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD4753 Guide for Evaluating, Selecting, and Specifying Bal-ances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD4767 Test Method for Consolidated Undrained TriaxialCompression Test for Cohesive SoilsD
18、6026 Practice for Using Significant Digits in GeotechnicalDataD6913 Test Methods for Particle-Size Distribution (Grada-tion) of Soils Using Sieve Analysis3. Terminology3.1 DefinitionsFor definitions of common technical termsin this standard, refer to Terminology D653.3.2 Definitions of Terms Specifi
19、c to This Standard:3.2.1 failurea stress condition selected to represent themaximum stress supported by a test specimen.3.2.1.1 DiscussionFailure is often taken to correspond tothe maximum principal stress difference (deviator stress) at-tained or the principal stress difference (deviator stress) at
20、15 % axial strain, whichever is obtained first during theperformance of a test.3.2.2 unconsolidated-undrained compressive strengththevalue of the principal stress difference (deviator stress) atfailure.3.2.3 unconsolidated-undrained shear strengththe valueof the principal stress difference (deviator
21、 stress) at failuredivided by two.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 p
22、ermittedfrom 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 is 100 % saturated, consolidationcannot occur when the confining pressure is applied nor
23、duringthe 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 unconsolidated-undrained shear stre
24、ngth.4.3 If the test specimens are partially saturated, orcompacted/reconstituted specimens, where the degree of satu-ration is less than 100 %, consolidation may occur when theconfining pressure is applied and during application of axialload, even though drainage is not permitted. Therefore, ifseve
25、ral partially saturated specimens of the same material aretested at different confining stresses, they will not have thesame unconsolidated-undrained shear strength.4.4 Mohr failure envelopes may be plotted from a series ofunconsolidated undrained triaxial tests. The Mohrs circles atfailure based on
26、 total stresses are constructed by plotting a halfcircle with a radius of half the principal stress difference(deviator stress) beginning at the axial stress (major principalstress) and ending at the confining stress (minor principalstress) on a graph with principal stresses as the abscissa andshear
27、 stress as the ordinate and equal scale in both directions.The failure envelopes will usually be a horizontal line forsaturated specimens and a curved line for partially saturatedspecimens.4.5 The unconsolidated-undrained shear strength is appli-cable to situations where the loads are assumed to tak
28、e place sorapidly that there is insufficient time for the induced pore-waterpressure to dissipate and for consolidation to occur during theloading period (that is, drainage does not occur).4.6 Compressive strengths determined using this proceduremay not apply in cases where the loading conditions in
29、 the fielddiffer significantly from those used in this test method.NOTE 3The quality of the results produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are ge
30、nerally considered capable of competenttesting. Users of this test method are cautioned that compliance withPractice D3740 does not ensure reliable results. Reliable results depend onseveral factors; Practice D3740 provides a means of evaluating some ofthose factors.5. Apparatus5.1 Axial Loading Dev
31、iceThe axial loading device 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 n
32、ot deviate by more than 65 % 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
33、of water placed on theloading 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 capable of measuring the axial loadto at least three significant digits (readability); have a full scaleaccuracy not to
34、 exceed 0.25 %; and a capacity that is notgreater than four times the axial load at failure. Commonly, anelectronic load cell is used and may be integrated with the axialloading device.5.3 Triaxial Compression ChamberThe triaxial chambershall consist of a top plate and a baseplate separated by acyli
35、nder. The cylinder shall be constructed of any materialcapable of withstanding the applied pressure. It is desirable 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 for
36、ced out of the chamber as it is filled. The base plate shallhave an inlet to fill the 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 axialD2850 152load at failure a
37、s measured in 8.6 and so there is negligiblelateral bending of the piston during loading.NOTE 5The use of two linear ball bushings to guide the piston isrecommended to reduce the friction and maintain alignment.NOTE 6A minimum piston diameter of one sixth the specimendiameter has been used successfu
38、lly in many laboratories to minimizelateral bending.5.5 Pressure-maintaining and Measurement DevicesThepressure-maintaining and measurement devices shall be ca-pable of applying, controlling, and measuring the chamberpressure to within 62 kPa (0.3 psi) for pressures less than 200kPa (29 psi) and to
39、within 61 % for pressures greater than 200kPa (29 psi).5.5.1 A pressure transducer measuring the applied chamberpressure shall have an accuracy not to exceed 60.25 % of fullrange, a capacity in excess of the applied chamber pressure,and a readability equivalent to at least three significant digits a
40、tthe maximum applied chamber pressure. This device com-monly consists of a reservoir connected to the triaxial chamberand partially filled with the chamber fluid (usually water), withthe upper part of the reservoir connected to a compressed gassupply; the gas pressure being controlled by a pressurer
41、egulator and measured by an electronic pressure transducer.5.6 Specimen Cap and BaseAn 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 c
42、ontact with the specimen and a circular crosssection. The mass of the specimen cap shall produce an axialstress on the specimen of less than 1 kPa (0.1 psi). Thediameter of the cap and base shall be equal to the initialdiameter of the specimen. The specimen base shall be con-nected to the triaxial c
43、ompression chamber to prevent lateralmotion or tilting, and the specimen cap shall be designed suchthat eccentricity of the piston-to-cap contact relative to thevertical axis of the specimen does not exceed 1.3 mm (0.05in.). The end of the piston and specimen cap contact area shallbe designed so tha
44、t tilting of the specimen cap during the testis minimal. The cylindrical surface of the specimen base andcap that contacts the membrane to form a seal shall be smoothand free of scratches.NOTE 7To determine the axial stress from the top cap, measure themass of the top cap in grams and area of the to
45、p cap in cm2. The stressfrom the top cap, in kN/m2(= kPa), is equal to the mass in grams timesthe acceleration due to gravity (9.8087 m/sec2) divided by the area in cm2times 10,000 cm2/m2divided by 1000 N/kN and 1000 g/kg.5.7 Deformation IndicatorThe vertical deformation of thespecimen is usually de
46、termined from the travel of the pistonacting on the top of the specimen. The piston travel shall bemeasured using a deformation indicator with a range of at least20 % of the initial height of the specimen and an accuracy notto exceed 0.25 % of the initial specimen height. The deforma-tion indicator
47、is commonly a linear variable differential trans-former (LVDT) or other measuring device meeting the require-ments for accuracy and range.5.8 Rubber MembraneThe rubber membrane used to en-case the specimen shall provide reliable protection againstleakage. Membranes shall be carefully inspected prior
48、 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 thickness shall notexceed 1 % of the diameter of the specimen. The membrane
49、shall 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 correcting theprincipal stress difference (deviator stress) for the effect of thestrength of the membrane is given in 8.8.5.9 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 minimum disturbance of the sampl
