ASTM D5311 - 11 Standard Test Method for Load Controlled Cyclic Triaxial Strength of Soil
Cyclic triaxial strength test results are used for evaluating the ability of a soil to resist the shear stresses induced in a soil mass due to earthquake or other cyclic loading.
Cyclic triaxial strength tests may be performed at different values of effective confining pressure on isotropically consolidated specimens to provide data required for estimating the cyclic stability of a soil.
Cyclic triaxial strength tests may be performed at a single effective confining pressure, usually equal to 14.5 lb/in. 2(100 kN/m2), or alternate pressures as appropriate on isotropically consolidated specimens to compare cyclic strength results for a particular soil type with that of other soils, Ref (2).
The cyclic triaxial test is a commonly used technique for determining cyclic soil strength.
Cyclic strength depends upon many factors, including density, confining pressure, applied cyclic shear stress, stress history, grain structure, age of soil deposit, specimen preparation procedure, and the frequency, uniformity, and shape of the cyclic wave form. Thus, close attention must be given to testing details and equipment.
1.1 This test method covers the determination of the cyclic strength (sometimes called the liquefaction potential) of saturated soils in either undisturbed or reconstituted states by the load-controlled cyclic triaxial technique.
1.2 The cyclic strength of a soil is evaluated relative to a number of factors, including: the development of axial strain, magnitude of applied cyclic stress, number of cycles of stress application, development of excess pore-water pressure, and state of effective stress. A comprehensive review of factors affecting cyclic triaxial test results is contained in the literature (1).
1.3 Cyclic triaxial strength tests are conducted under undrained conditions to simulate essentially undrained field conditions during earthquake or other cyclic loading.
1.4 Cyclic triaxial strength tests are destructive. Failure may be defined on the basis of the number of stress cycles required to reach a limiting strain or 100 % pore pressure ratio. See Section 3 for Terminology.
1.5 This test method is generally applicable for testing cohesionless free draining soils of relatively high permeability. When testing well-graded materials, silts, or clays, it should be recognized that pore-water pressures monitored at the specimen ends to not in general represent pore-water pressure values throughout the specimen. However, this test method may be followed when testing most soil types if care is taken to ensure that problem soils receive special consideration when tested and when test results are evaluated.
1.6 There are certain limitations inherent in using cyclic triaxial tests to simulate the stress and strain conditions of a soil element in the field during an earthquake.
1.6.1 Nonuniform stress conditions within the test specimen are imposed by the specimen end platens. This can cause a redistribution of void ratio within the specimen during the test.
1.6.2 A 90° change in the direction of the major principal stress occurs during the two halves of the loading cycle on isotropically consolidated specimens.
1.6.3 The maximum cyclic shear stress that can be applied to the specimen is controlled by the stress conditions at the end of consolidation and the pore-water pressures generated during testing. For an isotropically consolidated contractive (volume decreasing) specimen tested in cyclic compression, the maximum cyclic shear stress that can be applied to the specimen is equal to one-half of the initial total axial pressure. Since cohesionless soils are not capable of taking tension, cyclic shear stresses greater than this value tend to lift the top platen from the soil specimen. Also, as the pore-water pressure increases during tests performed on isotropically consolidated specimens, the effective confining pressure is reduced, contributing to the tendency of the specimen to neck during the extension portion of the load cycle, invalidating test results beyond that point.
1.6.4 While it is advised that the best possible undisturbed specimens be obtained for cyclic strength testing, it is sometimes necessary to reconstitute soil specimens. It has been shown that different methods of reconstituting specimens to the same density may result in significantly different cyclic strengths. Also, undisturbed specimens will almost always be stronger than reconstituted specimens.
1.6.5 The interaction between the specimen, membrane, and confining fluid has an influence on cyclic behavior. Membrane compliance effects cannot be readily accounted for in the test procedure or in interpretation of test results. Changes in pore-water pressure can cause changes in membrane penetration in specimens of cohesionless soils. These changes can significantly influence the test results.
1.6.6 The mean total confining pressure is asymmetric during the compression and extension stress application when the chamber pressure is constant. This is totally different from the symmetric stress in the simple shear case of the level ground liquefaction.
1.7 The values stated in both inch-pound and SI units are to be regarded separately as the standard. The values given in parentheses are for information only.
1.8 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.
2. Referenced Documents (purchase separately)
D422 Test Method for Particle-Size Analysis of Soils
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D854 Test Method for Specific Gravity of Soils
D1587 Practice for Thin-Walled Tube Sampling of Soils
D2216 Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock
D2850 Test Method for Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression
D4220 Practice for Preserving and Transporting Soil Samples
D4253 Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
D4254 Test Method for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density
D4318 Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
D4767 Test Method for Consolidated-Undrained Triaxial Compression Test on Cohesive Soils
consolidated-undrained tests; cohesionless soils; laboratory tests; liquefaction; triaxial tests; Axial strain; Cohesionless soil; Consolidated-undrained tests; Cyclic strength tests; Liquefaction; Load controlled cyclic triaxial technique; Loading tests--soil/related materials; Pore-water; Triaxial pressure
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