1.1 本试验方法涵盖了实验室使用压电陶瓷弯曲元件来确定土壤样本中的剪切波速。剪切波在土壤样本的一个边界处产生，然后在另一个边界处接收。测量剪切波传播时间，在已知传播距离上产生剪切波速度。根据该剪切波速和土壤样本的密度，确定初始剪切模量( G 最大值 )可以确定，这是弯曲元件测试的主要结果。 1.2 这种剪切波速测定涉及非常小的应变，对试样无破坏性。因此，可以在实验室测试期间的任何时间和任何次数确定弯曲元件剪切波速。 1.3 本试验方法描述了弯曲元件在三轴型式试验中的使用（例如，试验方法 D3999 , D4767 , D5311 或 D7181 )，但类似程序可用于其他实验室应用，如直接单剪（试验方法 D6528 )或固结仪试验（例如，试验方法 D2435 和 D4186 ). 剪切波速也可以在通过基质吸力固定在一起的无侧限土样本中确定。 1.4 剪切波速可以在三轴试验的不同方向上确定，例如垂直和水平方向。为确定剪切波速而产生的剪切波也可以在不同方向上极化，例如具有垂直或水平极化的水平传播剪切波。本试验方法描述了使用安装在三轴试样顶部压板和底座中的弯曲元件测量垂直方向的剪切波速。 如果在三轴试样的相对侧安装了额外的弯曲元件，则可以使用类似的程序来确定水平剪切波速。 1.5 提出并使用了各种不同的解释方法来评估土壤样本中的剪切波传播时间。本试验方法仅描述了其中两种，即使用发送至变送器弯曲器元件的单个正弦波信号的启动到启动和峰到峰。也可以使用产生类似结果的其他解释方法。 1.6 弯曲元件测量在某些情况下可能不太有效，例如在极硬的土壤中，产生的剪切波振幅可能非常小。 1.7 本试验方法不包括测定土壤样本中的纵波速度。该测量需要不同类型的压电陶瓷元件配置，这种测定通常在饱和软土样本中没有用处，因为到达饱和样本接收端的最早可识别压缩波很可能是通过（相对不可压缩的）样本孔隙水而不是（可压缩的）土壤骨架传输的。 1.8 单位- 以国际单位制表示的数值应视为标准值。 本标准不包括其他计量单位。 1.9 所有观察值和计算值应符合实践中确定的有效数字和舍入准则 D6026 ，除非被本试验方法取代。 1.9.1 用于规定如何在标准中收集/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。使用的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； 通常的做法是增加或减少报告数据的有效位数，以与这些考虑因素相称。考虑工程数据分析方法中使用的有效数字超出了这些测试方法的范围。 1.10 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、健康和环境实践，并确定监管限制的适用性。 1.11 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 初始剪切模量( G 最大值 )在小应变动态分析中，土壤样本在特定应力和时间条件下的变形是一个重要参数，例如预测土壤行为或土壤- 地震、爆炸和机器或交通振动期间的结构相互作用。 G 最大值 对于小应变循环情况，例如由风或波浪荷载引起的情况，也同样重要。小应变 G 最大值 对于大应变情况的非线性分析也至关重要，例如，较大应变土壤刚度的结果可能来自扭剪试验。剪切波速和 G 最大值 可用于在实验室测试程序中比较不同的土壤样本，也可用于比较实验室和现场测量的这些参数。 5.2 扭转共振柱试验（试验方法 D4015 )通常用于确定小于等于0.01%且可能略高于0.01%的小剪切应变下土壤样本的特性。谐振柱测试结果可包括 G 最大值 随时间变化，剪切模量随应变变化，阻尼比随时间变化，阻尼比随应变变化。弯曲元件测试只能提供其中的第一个， G 最大值 相对于时间。弯曲元件测试中的应变水平很小（恒定 G 最大值 应变水平），但由于材料和几何阻尼，应变幅值未知，且沿剪切波传播路径的应变不是恒定的。 因此，弯曲元件不能用于评估剪切模量与应变的关系，也不能提供有关阻尼比的信息。然而，弯曲元件可以纳入各种不同的实验室测试设备中，允许在特定测试条件下测量同一试样上的小应变和大应变刚度，并可能消除额外共振柱测试的需要。 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。 符合实践标准的机构 D3740 通常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惯例 D3740 本身并不能保证可靠的结果。可靠的结果取决于许多因素；实践 D3740 提供了一种评估其中一些因素的方法。

1.1 This test method covers the laboratory use of piezo-ceramic bender elements to determine the shear wave velocity in soil specimens. A shear wave is generated at one boundary of a soil specimen and then received at an opposite boundary. The shear wave travel time is measured, which over a known travel distance yields the shear wave velocity. From this shear wave velocity and the density of the soil specimen the initial shear modulus ( G max ) can be determined, which is the result of primary interest from bender element tests. 1.2 This shear wave velocity determination involves very small strains and is non-destructive to a test specimen. As such, bender element shear wave velocity determinations can be made at any time and any number of times during a laboratory test. 1.3 This test method describes the use of bender elements in a triaxial type test (for example, Test Methods D3999 , D4767 , D5311 , or D7181 ), but a similar procedure may be used for other laboratory applications, like in Direct Simple Shear (Test Method D6528 ) or oedometer tests (for example, Test Methods D2435 and D4186 ). Shear wave velocity can also be determined in unconfined soil specimens held together by matrix suction. 1.4 Shear wave velocity can be determined in different directions in a triaxial test, for example vertically and horizontally. Shear waves generated to determine shear wave velocity can also be polarized in different directions, for example a horizontally propagating shear wave with either vertical or horizontal polarization. This test method describes the use of bender elements mounted in the top platen and base pedestal of a triaxial test specimen to measure shear wave velocity in the vertical direction. With additional bender elements mounted on opposite sides of a triaxial specimen, a similar procedure may be used to determine horizontal shear wave velocity. 1.5 A variety of different interpretation methods to evaluate the shear wave travel time in a soil specimen have been proposed and used. This test method only describes two of these, Start to Start and Peak to Peak using a single sine wave signal sent to the transmitter bender element. Other interpretation methods producing similar results may also be used. 1.6 Bender element measurements may not work very well in some situations, like in extremely stiff soils where the generated shear wave amplitude may be exceedingly small. 1.7 This test method does not cover the determination of compressional wave velocity in soil specimens. This measurement requires a different type of piezo-ceramic element configuration, and such determinations are generally not useful in saturated soft soil specimens as the earliest identifiable compressional wave arrival at the receiver end of a saturated specimen will likely have been transmitted through the (relatively incompressible) specimen pore water rather than the (compressible) soil skeleton. 1.8 Units— The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.9 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 , unless superseded by this test method. 1.9.1 The procedures used to specify how data are collected/recorded and calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering data. 1.10 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 The initial shear modulus ( G max ) of a soil specimen under particular stress and time conditions is an important parameter in small-strain dynamic analyses such as those to predict soil behavior or soil-structure interaction during earthquakes, explosions, and machine or traffic vibrations. G max can be equally important for small-strain cyclic situations such as those caused by wind or wave loading. Small-strain G max is also vital for non-linear analyses of large strain situations, where the larger strain soil stiffness results could come from torsional shear tests, for example. Shear wave velocity and G max can be used to compare different soil specimens in a laboratory testing program, and also for comparing laboratory and field measurements of these parameters. 5.2 Torsional resonant column tests (Test Method D4015 ) are often used to determine properties of a soil specimen at small shear strains up to and possibly slightly beyond 0.01%. Resonant column test results can include G max versus time, shear modulus versus strain, damping ratio versus time and damping ratio versus strain. Bender element tests can only provide the first of these, G max versus time. The strain level in bender element tests is small (constant G max strain levels), but the strain magnitude is not known and the strain is not constant along the shear wave travel path due to material and geometric damping. Bender elements can therefore not be used to evaluate shear modulus versus strain and do not provide information about damping ratio. However, bender elements can be incorporated in a variety of different laboratory testing devices, allowing the measurement of small-strain and large-strain stiffness on the same specimen at the particular conditions of the test and possibly eliminating the need for additional resonant column tests. 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.