1.1本试验方法包括通过荷载控制循环三轴技术测定完整或重组状态下饱和土壤的循环强度（有时称为液化潜力）。 1.2土壤的循环强度与许多因素有关，包括:轴向应变的发展、施加循环应力的大小、应力施加的循环次数、超孔隙水压力的发展和有效应力的状态。文献中对影响循环三轴试验结果的因素进行了全面综述 (1) . 2. 1.3在不排水条件下进行循环三轴强度试验，以模拟地震或其他循环荷载期间基本不排水的现场条件。 1.4循环三轴强度试验具有破坏性。失效可根据达到极限应变或100所需的应力循环次数来定义 % 孔隙压力比。 参见第节 3. 用于术语。 1.5本试验方法通常适用于测试渗透性相对较高的无粘性自由排水土壤。测试级配良好的材料、淤泥或粘土时，在试样端部监测的孔隙水压力可能不代表整个试样的孔隙水压力值。然而，在测试大多数土壤类型时，如果注意确保在测试和评估测试结果时特别考虑问题土壤，则可以遵循此测试方法。 1.6所有观察值和计算值应符合实施规程D6026中制定的有效数字和舍入指南。实践D6026中用于指定如何收集、记录和计算数据的程序被视为行业标准。此外，它们代表了通常应保留的有效数字。这些程序不考虑材料变化、获取数据的目的、特殊目的研究或用户目标的任何考虑因素。 增加或减少报告数据的有效位数以符合这些考虑是常见做法。工程设计分析方法中使用的有效数字超出了本标准的范围。 1.6.1本标准中用于规定如何收集、计算或记录数据的方法与数据可用于设计或其他用途或两者的准确性没有直接关系。如何应用使用本标准获得的结果超出了其范围。 1.7以国际单位制或英寸-磅单位[括号内]表示的数值应单独视为标准值。每个系统中规定的值可能不是精确的等效值；因此，每个系统应相互独立使用。将两个系统的值合并可能会导致不符合标准。以国际单位制以外的单位报告试验结果不应视为不符合本试验方法。 1.8 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ====意义和用途====== 5.1循环三轴强度试验结果用于评估土壤抵抗因地震或其他循环荷载在土体中引起的剪应力的能力。 5.1.1可以在各向同性固结试样的不同有效围压值下进行循环三轴强度试验，以提供估计土壤循环稳定性所需的数据。 5.1.2循环三轴强度试验可在单个有效围压下进行，通常等于100 kN/m 2. [14.5磅/英寸。 2. ]，或在各向同性固结试样上适当的交替压力，以将特定土壤类型的循环强度结果与其他土壤的循环强度结果进行比较，参考 (2) . 5.2循环三轴试验是确定循环土壤强度的常用技术。 5.3循环强度取决于许多因素，包括密度、围压、施加的循环剪应力、应力历史、颗粒结构、土壤沉积年龄、试样制备程序以及循环波形的频率、均匀性和形状。因此，必须密切关注测试细节和设备。 5.4使用循环三轴试验模拟地震期间现场土壤元素的应力和应变条件有一定的固有局限性。 5.4.1试样内的不均匀应力条件由试样端板施加。这可能会导致试验期间试样内部孔隙比的重新分布。 5.4.2在各向同性固结试样上加载循环的两半期间，主应力方向发生90°变化。 5.4.3可施加在试样上的最大循环剪切应力由固结结束时的应力条件和试验期间产生的孔隙水压力控制。对于在循环压缩中测试的各向同性固结收缩（体积减小）试样，可施加在试样上的最大循环剪切应力等于初始总轴向压力的一半。由于无粘性土壤无法承受拉力，因此大于该值的循环剪切应力往往会将顶板从土样中抬起。此外，在对各向同性固结试样进行试验期间，随着孔隙水压力的增加，有效围压降低，导致试样在荷载循环的延长部分出现颈缩趋势，使超过该点的试验结果无效。 5.4.4虽然建议获得最佳完整试样进行循环强度试验，但有时有必要重建土壤试样。 已经表明，将试样重新组合到相同密度的不同方法可能会导致显著不同的循环强度。此外，完整样本几乎总是比复原样本更坚固。 5.4.5试样、薄膜和约束流体之间的相互作用对循环行为有影响。在测试程序或测试结果的解释中，无法很容易地解释膜顺应性影响。孔隙水压力的变化可能导致无粘性土壤样本中膜渗透的变化。这些变化会显著影响测试结果。 5.4.6当腔室压力恒定时，在施加压缩和拉伸应力期间，平均总围压是不对称的。这与水平地面液化的简单剪切情况下的对称应力完全不同。 注1 — 本标准产生的结果的质量取决于执行该标准的人员的能力，以及所用设备和设施的适用性。 符合实施规程D3740标准的机构通常被认为能够胜任和客观的测试/采样/检查等。本标准的用户应注意，遵守实施规程D3740本身并不能确保可靠的结果。可靠的结果取决于许多因素；实践D3740提供了评估其中一些因素的方法。

1.1 This test method covers the determination of the cyclic strength (sometimes called the liquefaction potential) of saturated soils in either intact 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) . 2 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, pore-water pressures monitored at the specimen ends may not 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 All observed and calculated values shall conform to the guide for significant digits and rounding established in Practice D6026. The procedures in Practice D6026 that are used to specify how data are collected, recorded, and calculated are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the objectives of the user. Increasing or reducing the significant digits of reported data to be commensurate with these considerations is common practice. Consideration of the significant digits to be used in analysis methods for engineering design is beyond the scope of this standard. 1.6.1 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. 1.7 The values stated in either SI units or inch-pound units [presented in brackets] are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method. 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. ====== Significance And Use ====== 5.1 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. 5.1.1 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. 5.1.2 Cyclic triaxial strength tests may be performed at a single effective confining pressure, usually equal to 100 kN/m 2 [14.5 lb/in. 2 ], 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) . 5.2 The cyclic triaxial test is a commonly used technique for determining cyclic soil strength. 5.3 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. 5.4 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. 5.4.1 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. 5.4.2 A 90° change in the direction of the major principal stress occurs during the two halves of the loading cycle on isotropically consolidated specimens. 5.4.3 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. 5.4.4 While it is advised that the best possible intact 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, intact specimens will almost always be stronger than reconstituted specimens. 5.4.5 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 porewater pressure can cause changes in membrane penetration in specimens of cohesionless soils. These changes can significantly influence the test results. 5.4.6 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. Note 1 — The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.