ASTM D2850 Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils, Thí nghiệm nén ba trục UU

ASTM D2850 Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils

ASTM D2850 Phương pháp thí nghiệm nén ba trục không cố kết không thoát nước UU

 

  1. Scope

1.1 This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of

either undisturbed or remolded cohesive soil. Specimens are subjected to a confining fluid pressure in a triaxial chamber. No drainage of the specimen is permitted during the test. The specimen is sheared in compression without drainage at a constant rate of axial deformation (strain controlled).

1.2 This test method provides data for determining undrained strength properties and stress-strain relations for soils.

This test method provides for the measurement of the total stresses applied to the specimen, that is, the stresses are not corrected for pore-water pressure

1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D 6026.

1.3.1 The method used to specify how data are collected, calculated, or recorded in this standard is not directly related to the accuracy to which the data can be applied in design or other uses, or both. How one applies the results obtained using this standard is beyond its scope.

1.4 The values stated in SI units are to be regarded as the standard. The values stated in inch-pound units and given in parentheses are approximate.

1.5 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.

 

  1. Referenced Documents

2.1 ASTM Standards: 2

D 422 Method for Particle-Size Analysis of Soils

D 653 Terminology Relating to Soil, Rock, and Contained Fluids

D 854 Test Method for Specific Gravity of Soils

D 1587 Method for Thin-Walled Tube Sampling of Soils

D 2166 Test Methods for Unconfined Compressive Strength of Cohesive Soil

D 2216 Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock

D 2487 Classification of Soils for Engineering Purposes

D 2488 Practice for Description and Identification of Soils (Visual-Manual Procedure)

D 3740 Practice for Evaluation of Agencies Engaged in the Testing and/or Inspection of Soil and Rock as Used in

Engineering Design and Construction

D 4220 Practices for Preserving and Transporting Soil Samples

D 4318 Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils

D 4753 Specification for Evaluating, Selecting, and Specifying Balances and Scales for Use in Testing Soil and

Rock, and Related Construction Materials

D 4767 Test Method for Consolidated-Undrained Triaxial Compression Test on Cohesive Soils2

D 6026 Practice for Using Significant Digits in Geotechnical Data

D 3740 Practice for Evaluation of Agencies Engaged in the Testing and/or Inspection of Soil and Rock as Used in

Engineering Design and Construction

D 4220 Practices for Preserving and Transporting Soil Samples

D 4318 Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils

D 4753 Specification for Evaluating, Selecting, and Specifying Balances and Scales for Use in Testing Soil and

Rock, and Related Construction Materials

D 4767 Test Method for Consolidated-Undrained Triaxial Compression Test on Cohesive Soils2

D 6026 Practice for Using Significant Digits in Geotechnical Data

 

  1. Terminology

3.1 Definitions—The definitions of terms used in this test method shall be in accordance with Terminology D 653.

3.2 Definitions of Terms Specific to This Standard:

3.2.1 failure—the stress condition at failure for a test specimen. Failure is often taken to correspond to the maximum principal stress difference (deviator stress) attained or the principal stress difference (deviator stress) at 15 % axial strain, whichever is obtained first during the performance of a test.

3.2.2 unconsolidated-undrained compressive strength—the value of the principal stress difference (deviator stress) at failure

 

  1. Significance and Use

4.1 In this test method, the compressive strength of a soil is determined in terms of the total stress, therefore, the resulting strength depends on the pressure developed in the pore fluid during loading. In this test method, fluid flow is not permitted from or into the soil specimen as the load is applied, therefore the resulting pore pressure, and hence strength, differs from that developed in the case where drainage can occur.

4.2 If the test specimens are 100 % saturated, consolidation cannot occur when the confining pressure is applied nor during the 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 and void ratio when they are tested, they will have approximately the same undrained shear strength. The Mohr failure envelope will usually be a  horizontal straight line over the entire range of confining stresses applied to the specimens if the specimens are fully saturated

4.3 If the test specimens are partially saturated or compacted specimens, where the degree of saturation is less than

100 %, consolidation may occur when the confining pressure is applied and during shear, even though drainage is not permitted. Therefore, if several partially saturated specimens of the same material are tested at different  confining stresses, they will not have the same undrained shear strength. Thus, the Mohr failure envelope for unconsolidated undrained triaxial tests on partially saturated soils is usually curved.

4.4 The unconsolidated undrained triaxial strength is applicable to situations where the loads are assumed to take place so rapidly that there is insufficient time for the induced pore-water pressure to dissipate and for consolidation to occur during the loading period (that is, drainage does not occur).

4.5 Compressive strengths determined using this procedure may not apply in cases where the loading conditions in the field differ significantly from those used in this test method

 

  1. Apparatus

5.1 Axial Loading Device

5.2 Axial Load-Measuring Device

5.3 Triaxial Compression Chamber

5.4 Axial Load Piston

5.5 Pressure Control Device

5.6 Specimen Cap and Base

5.7 Deformation Indicator

5.8 Rubber Membrane

5.9 Sample Extruder

5.10 Specimen Size Measurement Devices

5.11 Timer

5.12 Balances

5.13 Miscellaneous Apparatus

 

  1. Test Specimens

6.1 Specimen Size

6.2 Undisturbed Specimens

6.3 Compacted Specimens

 

  1. Procedure

7.1 Place the membrane on the membrane expander

7.2 With the specimen encased in the rubber membrane

7.3 Place the chamber in position in the axial loading device

7.4 If the axial load-measuring device is located outside of the triaxial chamber

7.5 Apply the axial load to produce axial strain

7.6 Record load and deformation values to three significant digits

7.7 After completion of the test, remove the test specimen from the chamber

7.8 Prior to placing the specimen

 

  1. Calculation

8.1 Meaurements and calculations shall contain three significant digits.

8.2 Calculate the axial strain, e (expressed as a decimal), for a given applied axial load

8.3 Calculate the average cross-sectional area, A, for a given applied axial load

8.4 Calculate the principal stress difference

8.5 Stress-Strain Curve

8.6 Correction for Rubber Membrane

8.7 Calculate the major and minor principal total stresses at failure

8.8 Calculate the initial degree of saturation of the test specimen using the initial mass and dimensions

 

  1. Report: Test Data Sheet(s)/Form(s)

9.1 The methodology used to specify how data are recorded on the data sheet(s)/form(s, as given below, is covered in 1.3.

9.2 Record as a minimum the following general information (data):

9.2.1 Identification data and visual description (Practice D 2488 or, if the information is available, Practice D 2487) of specimen including soil classification and whether the specimen is undisturbed, compacted, or otherwise prepared,

9.2.2 Values of plastic limit and liquid limit, if determined, in accordance with Test Method D 4318,

9.2.3 Value of specific gravity of solids and notation if the value was determined in accordance with Test Method D 854 or assumed,

9.2.4 Particle-size analysis, if determined, in accordance with Test Method D 422,

9.2.5 Initial height and diameter of the specimen.

9.2.6 Initial specimen dry unit weight, void ratio, water content, and saturation. (Specify if the water content was

obtained from cuttings, excess material, or the entire specimen.),

9.2.7 Rate of axial strain, percent per minute,

9.2.8 Axial strain at failure, percent,

9.2.9 The value of the compressive strength and the values of the minor and major principal stresses at failure, (Indicate when values have been corrected for membrane effects),

9.2.10 Stress-strain curve as described in 8.5,

9.2.11 Failure sketch or photograph of the specimen, and

9.2.12 Remarks and notations regarding any unusual conditions

 

  1. Precision and Bias

10.1 Precision—Test data on precision is not presented due to the nature of the soil materials tested by this procedure. It is either not feasible or too costly at this time to have ten or more laboratories participate in a round-robin testing program. Subcommittee D18.05 is seeking any data from users of this test method that might be used to make a limited statement on precision.

10.2 Bias—There is no accepted reference value for this test method; therefore, bias cannot be determined.

 

  1. Keywords

cohesive soil; lateral confinement; strain-controlled

loading; stress-strain relationships; total stresses; unconsolidated undrained strength

 

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ASTM D2850 Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils
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