D 2850

Designation: D 2850 – 95 (Reapproved 1999)

Standard Test Method for

Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils1
This standard is issued under the fixed designation D 2850; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

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 ispermitted 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 forpore-water pressure.
NOTE 1—The determination of the unconfined compressive strength of cohesive soils is covered by Test Method D 2166. NOTE 2—The determination of the consolidated, undrained strength of cohesive soils with pore pressure measurement is covered by Test Method D 4767.

D 2487 Classification of Soils for Engineering Purposes2 D 2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)2 D 3740 Practice for Evaluation of Agencies Engaged in the Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction2 D 4220 Practices for Preserving and Transporting Soil Samples2 D 4318 Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils2 D 4753 Specification for Evaluating, Selecting, and Specifying Balances and Scalesfor Use in Testing Soil and Rock, and Related Construction Materials2 D 4767 Test Method for Consolidated-Undrained Triaxial Compression Test on Cohesive Soils2 3. 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 testspecimen. 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. 4. Significance and Use4.1 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 thecase 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 haveapproximately the same undrained shear strength. The Mohr failure envelope

1.3 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. 1.4 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...