1、Designation: D7181 11Standard Test Method forConsolidated Drained Triaxial Compression Test for Soils1This standard is issued under the fixed designation D7181; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of strengthand stress-strain relationships of a cylindrical specimen ofeither intact o
3、r reconstituted soil. Specimens are consolidatedand sheared in compression with drainage at a constant rate ofaxial deformation (strain controlled).1.2 This test method provides for the calculation of princi-pal stresses and axial compression by measurement of axialload, axial deformation, and volum
4、etric changes.1.3 This test method provides data useful in determiningstrength and deformation properties such as Mohr strengthenvelopes. Generally, three specimens are tested at differenteffective consolidation stresses to define a strength envelope.1.4 If this test method is used on cohesive soil,
5、 a test maytake weeks to complete.1.5 The determination of strength envelopes and the devel-opment of relationships to aid in interpreting and evaluatingtest results are beyond the scope of this test method and mustbe performed by a qualified, experienced professional.1.6 All observed and calculated
6、 values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.6.1 The methods used to specify how data are collected,calculated, or recorded in this standard are regarded as theindustry standard. In addition, they are representative of thesignificant digit
7、s that generally should be retained. The proce-dures used do not consider material variations, purpose forobtaining the data, special purpose studies or any considerationof the end use. It is beyond the scope of this test method toconsider significant digits used in analysis methods for engi-neering
8、 design.1.7 UnitsThe values stated in SI units are to be regardedas standard. The inch-pound units given in parentheses aremathematical conversions, which are provided for informationpurposes only and are not considered standard. Reporting oftest results in units other than SI shall not be regarded
9、asnon-conformance with this test method.1.7.1 The gravitational system of inch-pound units is usedwhen dealing with inch-pound units. In this system, the pound(lbf) represents a unit of force (weight), while the unit for massis slugs. The slug unit is not given, unless dynamic (F = ma)calculations a
10、re involved.1.7.2 It is common practice in the engineering/constructionprofession to concurrently use pounds to represent both a unitof mass (lbm) and of force (lbf). This implicitly combines twoseparate systems of units: that is, the absolute system and thegravitational system. It is scientifically
11、 undesirable to combinethe use of two separate sets of inch-pound units within a singlestandard. As stated, this standard includes the gravitationalsystem of inch-pound units and does not use/present the slugunit for mass. However, the use of balances or scales recordingpounds of mass (lbm) or recor
12、ding density in lbm/ft3shall notbe regarded as non-conformance with this standard.1.7.3 The terms density and unit weight are often usedinterchangeably. Density is mass per unit volume whereas unitweight is force per unit volume. In this standard density isgiven only in SI units. After the density h
13、as been determined,the unit weight is calculated in SI or inch-pound units, or both.1.8 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user
14、 of this standard toestablish appropriate safety and health practices and deter-mine the applicability 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 ContainedFluidsD85
15、4 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD1587 Practice for Thin-Walled Tube Sampling of Soils forGeotechnical PurposesD2166 Test Method for Unconfined Compressive Strengthof Cohesive SoilD2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil
16、 and Rock by MassD2435 Test Methods for One-Dimensional Consolidation1This 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.Current edition approved July 1, 2011. Published Augus
17、t 2011. DOI: 10.1520/D71812For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100
18、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Properties of Soils Using Incremental LoadingD2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D2850 Test Method for Unconsolidated-Undrained TriaxialCompression Test
19、on Cohesive SoilsD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4220 Practices for Preserving and Transporting SoilSamplesD4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index o
20、f SoilsD4753 Guide for Evaluating, Selecting, and SpecifyingBalances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD4767 Test Method for Consolidated Undrained TriaxialCompression Test for Cohesive SoilsD6026 Practice for Using Significant Digits in GeotechnicalDataD726
21、3 Test Methods for Laboratory Determination of Den-sity (Unit Weight) of Soil Specimens3. Terminology3.1 DefinitionsRefer to Terminology D653 for standarddefinitions of common technical terms.3.2 Definitions of Terms Specific to This Standard:3.2.1 back pressure, na pressure applied to the specimenp
22、ore-water to cause air in the pore space to compress and topass into solution in the pore-water thereby increasing thepercent saturation of the specimen.3.2.2 effective consolidation stress, nthe difference be-tween the cell pressure and the pore-water pressure prior toshearing the specimen.3.2.3 fa
23、ilure, na maximum-stress condition or stress at adefined strain for a test specimen. Failure is often taken tocorrespond to the maximum principal stress difference (maxi-mum deviator stress) attained or the principal stress difference(deviator stress) at 15 % axial strain, whichever is obtained firs
24、tduring the performance of a test. Depending on soil behaviorand field application, other suitable failure criteria may bedefined, such as maximum effective stress obliquity, s1/s3max,or the principal stress difference (deviator stress) at a selectedaxial strain other than 15 %.4. Significance and U
25、se4.1 The shear strength of a saturated soil in triaxial com-pression depends on the stresses applied, time of consolidation,strain rate, and the stress history experienced by the soil.4.2 In this test method, the shear characteristics are mea-sured under drained conditions and are applicable to fie
26、ldconditions where soils have been fully consolidated under theexisting normal stresses and the normal stress changes underdrained conditions similar to those in the test method.4.3 The shear strength determined from this test method canbe expressed in terms of effective stress because a strain rate
27、 orload application rate slow enough to allow pore pressuredissipation during shear is used to minimize excess porepressure conditions. The shear strength may be applied to fieldconditions where full drainage can occur (drained conditions),and the field stress conditions are similar to those in the
28、testmethod.4.4 The shear strength determined from the test is com-monly used in embankment stability analyses, earth pressurecalculations, and foundation design.NOTE 1Notwithstanding the statements on precision and bias con-tained in this test method, the precision of this test method is dependent o
29、nthe competence of the personnel performing it and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD3740 are generally considered capable of competent testing. Users ofthis test method are cautioned that compliance with Practice D3740 doesnot ensure re
30、liable testing. Reliable testing depends on several factors;Practice D3740 provides a means of evaluating some of those factors.5. Apparatus5.1 The requirements for equipment needed to performsatisfactory tests are given in the following sections. See Fig.15.2 Axial Loading DeviceThe axial loading d
31、evice maybe a 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 axial strain (loading) prescribed in 8.4.2. The rate ofadvance of the loading device should not d
32、eviate by more than61 % from the selected value. Vibration due to the operationof the loading device shall be sufficiently small to not causedimensional changes in the specimen.NOTE 2A loading device may be judged to produce sufficiently smallvibrations if there are no visible ripples in a glass of
33、water placed on theloading platform when the device is operating at the speed at which thetest is performed.5.3 Axial Load-Measuring DeviceThe axial load-measuring device shall be an electronic load cell, hydraulicload cell, or any other load-measuring device capable of theaccuracy prescribed in thi
34、s paragraph and may be a part of theaxial loading device. The axial load-measuring device shall becapable of measuring the axial load to an accuracy of within1 % of the axial load at failure. If the load-measuring device islocated inside the triaxial compression chamber, it shall beinsensitive to ho
35、rizontal forces and to the magnitude of thechamber pressure.5.4 Triaxial Compression ChamberThe triaxial chambershall have a working chamber pressure capable of sustainingthe sum of the effective consolidation stress and the backpressure. It shall consist of a top plate and a base plateseparated by
36、a cylinder. The cylinder may be constructed ofany material capable of withstanding the applied pressures. It isdesirable to use a transparent material or have a cylinderprovided with viewing ports so the behavior of the specimenmay be observed. The top plate shall have a vent valve suchthat air can
37、be forced out of the chamber as it is filled. The baseplate shall have an inlet through which the pressure liquid issupplied to the chamber and inlets leading to the specimen baseand provide for connection to the cap to allow saturation anddrainage of the specimen when required.5.5 Axial Load Piston
38、The piston passing through the topof the chamber and its seal must be designed so the axial loadD7181 112due to friction does not exceed 0.1 % of the axial load at failureand so there is negligible lateral bending of the piston duringloading.NOTE 3The use of two linear ball bushings to guide the pis
39、ton isrecommended to minimize friction and maintain alignment.NOTE 4A minimum piston diameter of16 the specimen diameter hasbeen used successfully in many laboratories to minimize lateral bending.5.6 Pressure and Vacuum-Control DevicesThe chamberpressure and back pressure control devices shall be (a
40、) capableof applying and controlling pressures to within 62 kPa (0.25lbf/in.2) for effective consolidation pressures less than 200 kPa(28 lbf/in.2) and to within 61 % for effective consolidationpressures greater than 200 kPa, and (b) able to maintain theeffective consolidation stress within 2 % of t
41、he desired value(Note 5). The vacuum-control device shall be capable ofapplying and controlling partial vacuums to within 62 kPa.The devices may consist of pneumatic-pressure regulators,combination pneumatic pressure and vacuum regulators, or anyother device capable of applying and controlling press
42、ures orpartial vacuums to the required tolerances. These tests canrequire a duration of several days, therefore, an externalair/water interface is recommended for both the chamber-pressure or back-pressure systems.NOTE 5Many laboratories use differential pressure regulators andtransducers to achieve
43、 the requirements for small differences betweenchamber and back pressure.5.7 Pressure- and Vacuum-Measurement DevicesThechamber pressure-, back pressure-, and vacuum-measuringdevices shall be capable of measuring the ranges of pressuresor partial vacuums to the tolerances given in 5.6. They mayconsi
44、st of electronic pressure transducers, or any other devicecapable of measuring pressures, or partial vacuums to thestated tolerances. If separate devices are used to measure thechamber pressure and back pressure, the devices must benormalized simultaneously and against the same pressuresource. Since
45、 the chamber and back pressure are the pressurestaken at the midheight of the specimen, it may be necessary toadjust the zero-offset of the devices to reflect the hydraulichead of fluids in the chamber and back pressure controlsystems.5.8 Volume Change Measurement DeviceThe volume ofwater entering o
46、r leaving the specimen shall be measured withan accuracy of within 60.05 % of the total volume of thespecimen. The volume-measuring device is usually a buretteconnected to the back pressure but may be any other devicemeeting the accuracy requirement. The device must be able towithstand the maximum b
47、ack pressure and of sufficient capac-ity for the performance of the test. Volume changes duringshear are often on the order of 620 % or more of the specimenvolume. Either allowing for resetting of the system duringshear or having a total capacity capable of measuring the entirechange may meet the re
48、quired capacity.5.9 Deformation IndicatorThe vertical deformation of thespecimen is usually determined from the travel of the pistonacting on the top of the specimen. The piston travel shall bemeasured with an accuracy of at least 0.25 % of the initialspecimen height. The deformation indicator shall
49、 have a rangeof at least 20 % of the initial height of the specimen and maybe a dial indicator, linear variable differential transformer(LVDT), extensometer, or other measuring device meeting therequirements for accuracy and range.5.10 Specimen Cap and BaseThe specimen cap and baseshall be designed to provide drainage from both ends of thespecimen. They shall be constructed of a rigid, noncorrosive,impermeable material, and each shall, except for the drainageprovision, have a circular plane surface of contact with theFIG. 1 Schematic Diagram of a Typical Consolidat
