1、Standard Method of Test for Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression AASHTO Designation: T 296-10 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 296-1 AASHTO St
2、andard Method of Test for Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression AASHTO Designation: T 296-10 1. SCOPE 1.1. This test method covers the determination of unconsolidated strength and stressstrain relationships for a cylindrical specimen of either an un
3、disturbed or remolded cohesive soil sheared undrained in compression at a constant rate of axial deformation (strain controlled). 1.2. The test method provides for the calculation of total stresses on, and axial compression of, the test specimen by measurement of axial load and axial deformation. 1.
4、3. The test provides data useful in determining strength and deformation properties of cohesive soils much as Mohr strength envelopes and Youngs modulus. 1.4. The determination of strength envelopes and the development of relationships to aid in interpreting and evaluating test results are left to t
5、he engineer or office requesting the test. 1.5. The values stated in SI units are to be regarded as standard. 1.6. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the respons
6、ibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 89, Determining the Liquid Limit of Soils T 90, Determining the Plastic Limit and Plastic
7、ity Index of Soils T 100, Specific Gravity of Soils T 207, Thin-Walled Tube Sampling of Soils T 208, Unconfined Compressive Strength of Cohesive Soil T 297, Consolidated, Undrained Triaxial Compression Test on Cohesive Soils 2.2. ASTM Standards: D422, Standard Test Method for Particle-Size Analysis
8、of Soils D653, Standard Terminology Relating to Soil, Rock, and Contained Fluids D2216, Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplicat
9、ion is a violation of applicable law.TS-1a T 296-2 AASHTO D2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) D4220/D4220M, Standard Practices for Preserving and Transporting Soil Samples 2.3. Other Standards and References: USBR 5754 Pr
10、ocedure for Unconsolidated-Undrained Triaxial Shear Testing of Soils. (See Earth Manual, Part 2.) Joseph E. Bowles, Engineering Properties of Soils and their Measurement, McGraw-Hill Book Company, New York, p. 158, 3rd Edition. 3. TERMINOLOGY 3.1. DefinitionsThe definitions of terms used in this tes
11、t method shall be in accordance with ASTM D653. 3.2. Description of Terms Specific to This Standard: 3.2.1. failurethe stress condition at failure for a test specimen. Failure is often taken to correspond to the maximum principal stress difference (maximum deviator stress) attained or the principal
12、stress difference (deviator stress) at 15 percent axial strain, whichever is obtained first during the performance of a test. Depending on soil behavior and field application, other suitable failure criteria may be defined, such as the principal stress difference (deviator stress) at a selected axia
13、l strain other than 15 percent. 3.2.2. principal stress difference (deviator stress)the difference in magnitude between the major principal stress and minor principal stress; in a triaxial compression test, the stress due to the axial load that is applied in excess of the confining pressure. 3.2.3.
14、total stress, the total force per unit area acting within a soil mass. It is the sum of neutral and effective stresses ( + ). 4. SIGNIFICANCE AND USE 4.1. The strength in this test is measured under undrained conditions and is applicable to field conditions where soils are subjected to a change in s
15、tress without time for consolidation to take place (unconsolidated condition), and the field stress conditions are similar to those in the tests. 4.2. The shear strength determined from the test expressed in terms of total stresses or effective stresses is commonly used in embankment stability analy
16、ses, earth pressure calculations, and foundation design. 5. APPARATUS 5.1. The requirements for equipment needed to perform satisfactory tests are given in the following sections. 5.2. Axial Loading DeviceThe axial compression device may be a screw jack driven by an electric motor through a geared t
17、ransmission, a hydraulic or pneumatic loading device, or any other compression device with sufficient capacity and control to provide the rate of axial strain (loading) described in Section 8.2.6. The rate of advance of the loading device should not deviate by more than 1 percent from the selected v
18、alue. Vibration due to the operation of the loading device shall 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 296-3 AASHTO be sufficiently small to not cause dimensional changes in the specime
19、n or to produce changes in pore-water pressure when the drainage valves are closed. Note 1A loading device may be judged to produce sufficiently small vibrations if there are no visible ripples in a glass of water placed on the loading platform when the device is operating. 5.3. Axial Load-Measuring
20、 DeviceThe axial load-measuring device may be a load ring, electronic load cell, hydraulic load cell, or any other load-measuring device capable of the accuracy prescribed in this paragraph and may be a part of the axial loading device. The axial load-measuring device shall be capable of measuring t
21、he axial load to an accuracy of within 1 percent of the axial load at failure. If the load-measuring device is located inside the triaxial compression chamber, it shall be insensitive to horizontal forces and to the magnitude of the chamber pressure. 5.4. Triaxial Compression ChamberThe triaxial cha
22、mber must be able to withstand a chamber pressure equal to the sum of the effective confining pressure and back pressure. It shall consist of a top plate and a baseplate separated by a cylinder. The cylinder may be constructed of any material capable of withstanding the applied pressures. It is desi
23、rable to use a transparent material or have a cylinder provided with viewing ports so the behavior of the specimen may be observed. The top plate shall have a vent valve such that air can be forced out of the chamber as it is filled. The baseplate shall have an inlet through which pressure liquid is
24、 supplied to the chamber. Note 2Although the confining fluid for this test is typically a liquid, compressed air or other gases may be successfully used. Use of air or other gases is a safety concern, however, about which the user must be aware and take reasonable safeguards. 5.5. Axial Load PistonT
25、he piston passing through the top of the chamber and its seal must be designed so the variation in axial load due to friction does not exceed 0.1 percent of the axial load at failure and so there is negligible lateral bending of the piston during loading. Note 3The use of two linear ball bushings to
26、 guide the piston is recommended to minimize friction and maintain alignment. Note 4A minimum piston diameter of one sixth of the specimen diameter has been used successfully in many laboratories to minimize lateral bending. 5.6. Chamber Pressure Control DeviceThe chamber pressure control device sha
27、ll be capable of applying and controlling pressure to within 2 kPa (0.25 psi) for chamber pressures less than 200 kPa (28 psi) and to within 1 percent for chamber pressures greater than 200 kPa (28 psi). The device may consist of self-compensating mercury pots, a pneumatic pressure regulator, or any
28、 other device capable of applying and controlling pressures to the required tolerances. 5.7. Chamber Pressure Measurement DeviceThe chamber pressure measuring device shall be capable of measuring pressures to the tolerances given in Section 5.6. It may be a Bourdon gauge, pressure manometer, electro
29、nic pressure transducer, or any other device capable of measuring pressures to the stated tolerances. 5.8. Deformation IndicatorThe vertical deformation of the specimen is usually determined from the travel of the piston acting on the top of the specimen. The piston travel shall be measured with an
30、accuracy of at least 0.02 percent of the initial specimen height. The deformation indicator shall have a travel range of at least 20 percent of the initial height of the specimen and may be a dial indicator, linear variable differential transformer (LVDT), extensiometer, or other measuring device me
31、eting the requirements for accuracy and range. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 296-4 AASHTO 5.9. Specimen Cap and Base: 5.9.1. For Total Stress DeterminationAn impermeable rigid c
32、ap and base shall be used to prevent drainage of the specimen. The specimen cap and base shall be constructed of a noncorrosive impermeable material and each shall have a circular plane surface of contact with the specimen and a circular cross section. The weight of the specimen cap shall produce an
33、 axial stress on the specimen of less than 1 kN/m2(0.145 psi). The diameter of the cap and base shall be equal to the initial diameter of the specimen. The specimen base shall be coupled to the triaxial compression chamber so as to prevent lateral motion or tilting and the specimen cap shall be desi
34、gned to receive the piston such that the piston-to-cap contact area is concentric with the cap. The specimen cap during shear shall not tilt more than 5 degrees. The cylindrical surface of the specimen base and cap that contacts the membrane to form a seal shall be smooth and free of scratches. Note
35、 5The stress produced by the specimen cap can exceed 1 kN/m2(0.145 psi) provided the test data is corrected for the effects of that stress. 5.10. Rubber MembraneThe rubber membrane used to encase the specimen shall provide reliable protection against leakage. To check a membrane for leakage, the mem
36、brane shall be placed around a cylindrical form, sealed at both ends with rubber O-rings, subjected to a small air pressure on the inside, and immersed in water. If air bubbles appear from any point on the membrane it shall be rejected. To offer minimum restraint to the specimen, the unstretched mem
37、brane diameter shall be between 90 and 95 percent of that of the specimen. The membrane thickness shall not exceed 1 percent of the diameter of the specimen. The membrane shall be sealed to the specimen cap and base with rubber O-rings for which the unstressed inside diameter is between 75 and 85 pe
38、rcent of the diameter of the cap and base, or by other means that will provide a positive seal. An equation for correcting the principal stress difference (deviator stress) for the effect of the stiffness of the membrane is given in Section 10.4.3. 5.11. Specimen-Size Measurement DevicesDevices used
39、 to determine the height and diameter of the specimen shall measure the respective dimensions to within 0.1 percent of the total dimension and shall be constructed such that their use will not disturb the specimen. Note 6Circumferential measuring tapes are recommended over calipers for measuring the
40、 diameter. 5.12. RecordersSpecimen behavior may be recorded manually or by electronic digital or analog recorders. If electronic recorders are used, it shall be necessary to calibrate the measuring devices through the recorder using known input standards. 5.13. Sample ExtruderHand-operated, mechanic
41、al, and hydraulic extruders are acceptable provided the device (1) is capable of extruding the soil core from the sampling tube in the same direction of travel in which the sample entered the tube, (2) has a length of travel at least equal to the required untrimmed test length of the sample and perm
42、its the extrusion to occur in one operation without resetting the piston or extrusion mechanism, (3) can be operated at a relatively uniform rate, and (4) causes negligible disturbance of the sample. 5.14. Weighing DeviceThe specimen weighing device shall determine the mass of the specimen to an acc
43、uracy of within 0.05 percent of the total mass of the specimen. 5.15. Testing EnvironmentThe shear portion of the test shall be performed in an environment where temperature fluctuations are less than 4C (7.2F) and there is no direct contact with sunlight. 5.16. Miscellaneous ApparatusSpecimen trimm
44、ing and carving tools including a wire saw, steel straightedge, miter box, and vertical trimming lathe, apparatus for preparing compacted specimens, membrane and O-ring expander, water content cans, and data sheets shall be provided as required. 2015 by the American Association of State Highway and
45、Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 296-5 AASHTO 6. TEST SPECIMEN PREPARATION 6.1. Specimen SizeSpecimens shall be cylindrical and have a minimum diameter of 3.3 cm (1.3 in.). The height-to-diameter ratio shall be between 2 and 2.5. The
46、largest particle size shall be smaller than one sixth of the specimen diameters. If, after completion of a test, it is found based on visual observation that oversize particles are present, indicate this information in the report of test data (Section 11.1.20). Note 7If oversize particles are found
47、in the specimen after testing, a particle-size analysis may be performed in accordance with ASTM D422 to confirm the visual observation and the results provided with the test report (Section 11.1.4). 6.2. Undisturbed SpecimensPrepare undisturbed specimens from large undisturbed samples or from sampl
48、es secured in accordance with T 207 or other acceptable undisturbed tube sampling procedures and preserved and transported in accordance with the practices for Group C samples in ASTM D4220/D4220M. Specimens obtained by tube sampling may be tested without trimming except for cutting the end surfaces
49、 plane and perpendicular to the longitudinal axis of the specimen, provided soil characteristics are such that no significant disturbance results from sampling. Handle specimens carefully to minimize disturbance, changes in cross section, or change in water content. If compression or any type of noticeable disturbance would be caused by the extrusion device, split the sample tube lengthwise or cut the tube in suitable sections to facilitate removal of the specimen with minimum disturbance. Prepare trimmed specimens,
