1.1这些试验方法包括通过荷载或行程控制的循环三轴技术测定完整或重建状态下土壤的模量和阻尼特性。本标准的重点是确定静水固结、不排水条件下土壤的这些特性。 1.2初始饱和或非饱和土试样的循环三轴特性是相对于许多因素进行评估的，这些因素包括:应变水平、密度、循环次数、材料类型和有效应力。 1.3这些试验方法适用于统一土壤分类系统或规程D2487中定义的细粒土和粗粒土。 试样可以是完整的，也可以在实验室中通过压实进行重组。 1.4提供了两种试验方法，用于使用循环加载器确定正割杨氏模量( E )和阻尼系数( D )对于土壤样本。第一种试验方法（A）允许测定 E 和 D 使用恒定负载装置。第二种试验方法（B）允许测定 E 和 D 使用恒定行程装置。试验方法如下: 1.4.1 试验方法A- 本试验方法要求对试样施加恒定的循环载荷。它用于确定恒定负载条件下的割线杨氏模量和阻尼系数。 1.4.2 试验方法B- 本试验方法要求对试样施加恒定循环变形。它用于确定恒定冲程条件下的割线杨氏模量和阻尼系数。 1.5帮助解释和评估测试结果的关系开发由工程师或要求测试的办公室负责。 1.6 限制- 使用循环三轴试验模拟地震期间现场土壤单元的应力和应变条件有一定的固有局限性，以下几节总结了其中的一些局限性。在适当考虑影响试验结果的因素后，仔细进行的循环三轴试验可以提供土壤循环行为的数据，其精度足以对剪切应变水平0以下的模量和阻尼系数进行有意义的评估。 5. %. 1.6.1试样内的不均匀应力条件由试样端板施加。 1.6.2在各向同性约束试样上加载循环的两半期间，主应力方向发生90°变化。 1.6.3可应用于饱和试样的最大循环轴向应力由围压应用结束时的应力条件和不排水压缩过程中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约束试样，可施加在试样上的最大循环轴向应力等于有效围压。由于无粘性土壤无法抵抗张力，大于该值的循环轴向应力往往会将顶部压板从土样中抬起。 此外，在对各向同性约束试样进行试验期间，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。 1.6.4虽然建议获得尽可能好的完整试样进行循环试验，但有时有必要重建土壤试样。已经表明，将样本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行为。此外，完整的样本几乎总是比相同密度的重组样本更坚固、更坚硬。 1.6.5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。 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- 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所有观察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。 1.8.1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。 1.9 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循环三轴试验允许在静水固结、不排水条件下测定棱柱土试样循环轴向荷载的割线模量和阻尼系数。该试验得出的割线模量和阻尼系数可能不同于在相同材料上进行扭剪试验得出的割线模量和阻尼系数。 5.2割线模量和阻尼系数是天然和工程结构在动态或循环载荷（如地震、海浪或爆炸引起的载荷）下的动态性能评估中使用的重要参数。这些参数可用于动态响应分析，包括有限元、有限差分和线性或非线性- 线性分析方法。 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 These test methods cover the determination of the modulus and damping properties of soils in either intact or reconstituted states by either load or stroke controlled cyclic triaxial techniques. The standard is focused on determining these properties for soils in hydrostatically consolidated, undrained conditions. 1.2 The cyclic triaxial properties of initially saturated or unsaturated soil specimens are evaluated relative to a number of factors including: strain level, density, number of cycles, material type, and effective stress. 1.3 These test methods are applicable to both fine-grained and coarse-grained soils as defined by the unified soil classification system or by Practice D2487. Test specimens may be intact or reconstituted by compaction in the laboratory. 1.4 Two test methods are provided for using a cyclic loader to determine the secant Young's modulus ( E ) and damping coefficient ( D ) for a soil specimen. The first test method (A) permits the determination of E and D using a constant load apparatus. The second test method (B) permits the determination of E and D using a constant stroke apparatus. The test methods are as follows: 1.4.1 Test Method A— This test method requires the application of a constant cyclic load to the test specimen. It is used for determining the secant Young's modulus and damping coefficient under a constant load condition. 1.4.2 Test Method B— This test method requires the application of a constant cyclic deformation to the test specimen. It is used for determining the secant Young's modulus and damping coefficient under a constant stroke condition. 1.5 The development of relationships to aid in interpreting and evaluating test results are left to the engineer or office requesting the test. 1.6 Limitations— 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, with several summarized in the following sections. With due consideration for the factors affecting test results, carefully conducted cyclic triaxial tests can provide data on the cyclic behavior of soils with a degree of accuracy adequate for meaningful evaluations of modulus and damping coefficient below a shearing strain level of 0.5 %. 1.6.1 Nonuniform stress conditions within the test specimen are imposed by the specimen end platens. 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 confined specimens. 1.6.3 The maximum cyclic axial stress that can be applied to a saturated specimen is controlled by the stress conditions at the end of confining stress application and the pore-water pressures generated during undrained compression. For an isotropically confined specimen tested in cyclic compression, the maximum cyclic axial stress that can be applied to the specimen is equal to the effective confining pressure. Since cohesionless soils cannot resist tension, cyclic axial 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 confined 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 intact specimens be obtained for cyclic 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 behavior. Also, intact specimens will almost always be stronger and stiffer than reconstituted specimens of the same density. 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. 1.7 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 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. 1.8.1 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. 1.9 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 The cyclic triaxial test permits determination of the secant modulus and damping coefficient for cyclic axial loading of a prismatic soil specimen in hydrostatically consolidated, undrained conditions. The secant modulus and damping coefficient from this test may be different from those obtained from a torsional shear type of test on the same material. 5.2 The secant modulus and damping coefficient are important parameters used in dynamic, performance evaluation of both natural and engineered structures under dynamic or cyclic loads such as caused by earthquakes, ocean wave, or blasts. These parameters can be used in dynamic response analyses including, finite elements, finite difference, and linear or non-linear analytical methods. 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.