1.1 本试验方法包括定量测定土壤细粒部分的粒度分布。使用比重计沉降法测定比200号（75µm）筛细且大于约0.2µm的材料的粒度分布（级配）。对通过10号（2.0 mm）或更细筛的材料进行试验，结果显示为该分数的质量百分比与粒径对数。 1.2 该方法可用于评估精细度- 通过将沉降结果与使用D6913的筛分分析结果相结合，获得完整级配曲线，获得具有广泛粒径的土壤的颗粒分数。当不存在粗粒颗粒或粗粒材料的级配不需要或不需要时，也可以使用该方法。 注1: 本试验方法中记录的有效数字排除了获得不含大量细粒的材料的粒度分布。例如，干净的沙子不会产生可检测数量的淤泥和粘土大小的颗粒，因此不应使用此方法进行测试。 沉降样品中的最小细粒量为15 g。 1.3 当结合沉降和筛分试验的结果时，将通过更通用的试验方法（如试验方法）提供获得沉降分析材料和计算结果的程序 D6913 ( 注释2 ). 注2: 小组委员会D18.03目前正在开发一种新的测试方法“结合筛分和沉淀技术的土壤粒度分析测试方法” 1.4 术语“土壤”和“材料”在整个标准中互换使用。 1.5 沉降分析基于较大颗粒比较小颗粒更快地通过流体的概念。斯托克斯定律给出了一个控制方程，用于确定球形粒子通过静止液体的最终速度。终点速度与颗粒直径的平方成正比。因此，在液体容器中沉降时，颗粒在时间和位置上都按大小进行分类。 1.5.1 斯托克斯定律有几个假设:粒子是球形且光滑的；粒子之间没有干扰； 容器中部和两侧的电流没有差别；流动为层流；粒子密度相同。这些假设适用于各种形状和尺寸的土壤颗粒。 1.6 比重计用于测量流体密度，并确定在特定时间和位置悬浮的颗粒数量。土壤水悬浮液的密度取决于土壤颗粒的浓度和比重以及添加的分散剂的量。在经过的时间内进行的每个比重计测量用于计算比斯托克斯定律给出的直径更细的颗粒百分比。 该系列读数提供了材料质量随粒径变化的分布。 1.7 本试验方法不包括样品的采购或在获得缩减样品之前的样品处理。假设样品是使用适当的方法获得的，并且代表现场材料或条件。还假设已对样品进行处理，以使减少的样品准确反映该材料更细部分的粒度分布（级配）。 1.8 材料加工- 材料在潮湿或接收状态下进行测试，除非材料在空气干燥状态下接收。应使用湿制备方法从还原样品中获得沉降试样。仅当材料以风干状态接收时，才允许风干制备。使用的方法可由请求机构指定；但是，应使用湿制备方法进行鉴定试验。 1.9 本试验方法为 不 适用于以下土壤: 1.9.1 含有纤维状泥炭的土壤。 1.9.2 土壤含水量约为5 % 细粒材料( 注1 ). 1.9.3 含有外来物质的土壤，如有机溶剂、油、沥青、木材碎片或类似物品( 附注3 ). 注3: 如果外来物质（如木材）可以很容易地用手清除，则允许这样做。然而，在某些情况下，外来物质可能作为材料的一部分进行评估，不应从材料中移除。 1.9.4 含有水泥成分的材料，如水泥、粉煤灰、石灰或其他稳定外加剂。 1.10 对于以下土壤，本试验方法可能无法在实验室内和实验室之间产生一致的试验结果。为了测试这些土壤，必须调整该测试方法，并记录这些调整。 1.10.1 沉降过程中絮凝的土壤。可能需要对这些材料进行处理以降低盐度或改变悬浮液的pH值。 1.10.2 处理改变土壤级配的易碎土壤。这些土壤的典型示例是一些残积土、风化最严重的页岩、风化花岗岩和一些弱胶结土壤。 1.10.3 不易分散的土壤，如海绿石粘土或一些干燥的塑性粘土。 1.11 可使用该方法测试非土壤但由颗粒组成的样品。应用本标准时应使用上述适用章节。 1.12 单位- 以国际单位制表示的数值应视为标准值。除筛网名称外，根据实践使用“替代”系统对其进行识别 E11 ，例如3英寸。和第200号，而不是分别为75 mm和75µm的“标准”名称。 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。使用记录质量磅（lbm）的天平或天平不应视为不符合本标准。 1.13 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。 1.13.1 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。考虑工程或其他数据分析方法中使用的有效数字超出了本测试方法的范围。 1.14 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。 1.15 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 粒径分布（级配）是一个描述性术语，指在指定粒径范围内分布的土壤干质量比例。使用该方法生成的级配曲线根据粒度定义，而不是矿物学或阿太堡极限分类，得出土壤中存在的粉土和粘土粒度分数的分布。 5.2 除非沉降样品代表整个样品，否则沉降结果必须与筛分分析相结合，以获得完整的粒度分布。 5.3 粘土粒径分数是比2µm细的材料。粘土粒径分数与塑性指数（试验方法）结合使用 D4318 )计算放射性，从而指示粘土部分的矿物学。 5.4 粉土和粘土粒级的级配是决定细粒土敏感性的重要因素- 颗粒土的冻结作用。 5.5 土壤的级配是工程特性的指标，如导水率、压缩性和抗剪强度。然而，用于工程和其他目的的土壤行为取决于许多因素，例如有效应力、矿物类型、结构、塑性和地质成因，不能仅基于级配。 5.6 某些类型的土壤需要特殊处理，以正确确定粒径。例如，化学胶结剂可以将粘土颗粒粘合在一起，应尽可能处理以去除胶结剂。 过氧化氢和适度加热可以消化有机物。盐酸可以通过洗涤去除碳酸盐，连二亚硫酸钠柠檬酸-碳酸氢盐萃取可以用于去除氧化铁。可使用试验水进行浸出，以降低盐浓度。然而，在进行沉降试验时，所有这些处理都会增加大量的时间和精力，是允许的，但不在本试验方法的范围内。 5.7 沉降试验的尺寸限制为约100µm至约0.1µm。在比重计上获得稳定初始读数所需的时间长度控制结果的上限，而试验持续时间控制下限。 5.8 晶粒的形状和密度对结果很重要。假设斯托克斯定律适用于球形颗粒，即使细粉土和粘土大小的颗粒更可能是板状的，并且比较大的颗粒具有更大的矿物密度。 5.9 高塑性粘土在其表面形成结构性水层。据张和陆说 3. 这种近地表水的密度可高达1.4 g/L。这种高密度结构水会导致该测试方法中出现错误，并使粒度分布曲线向上移动。 结构性水的校正超出了本标准的范围，但通过率超过100% % 是可能的，不应排除在报告之外。 注5: 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 quantitative determination of the distribution of particle sizes of the fine-grained portion of soils. The sedimentation by hydrometer method is used to determine the particle-size distribution (gradation) of the material that is finer than the No. 200 (75-µm) sieve and larger than about 0.2-µm. The test is performed on material passing the No. 10 (2.0-mm) or finer sieve and the results are presented as the mass percent finer of this fraction versus the log of the particle diameter. 1.2 This method can be used to evaluate the fine-grained fraction of a soil with a wide range of particle sizes by combining the sedimentation results with results from a sieve analysis using D6913 to obtain the complete gradation curve. The method can also be used when there are no coarse-grained particles or when the gradation of the coarse-grained material is not required or not needed. Note 1: The significant digits recorded in this test method preclude obtaining the grain size distribution of materials that do not contain a significant amount of fines. For example, clean sands will not yield detectable amounts of silt and clay sized particles, and therefore should not be tested with this method. The minimum amount of fines in the sedimentation specimen is 15 g. 1.3 When combining the results of the sedimentation and sieve tests, the procedure for obtaining the material for the sedimentation analysis and calculations for combining the results will be provided by the more general test method, such as Test Methods D6913 ( Note 2 ). Note 2: Subcommittee D18.03 is currently developing a new test method “Test Method for Particle-Size Analysis of Soils Combining the Sieve and Sedimentation Techniques.” 1.4 The terms “soil” and “material” are used interchangeably throughout the standard. 1.5 The sedimentation analysis is based on the concept that larger particles will fall through a fluid faster than smaller particles. Stokes’ Law gives a governing equation used to determine the terminal velocity of a spherical particle falling through a stationary liquid. The terminal velocity is proportional to the square of the particle diameter. Therefore, particles are sorted by size in both time and position when settling in a container of liquid. 1.5.1 Stokes’ Law has several assumptions which are: the particles are spherical and smooth; there is no interference between the particles; there is no difference between the current in the middle of the container and the sides; flow is laminar; and the particles have the same density. These assumptions are applied to soil particles of various shapes and sizes. 1.6 A hydrometer is used to measure the fluid density and determine the quantity of particles in suspension at a specific time and position. The density of the soil-water suspension depends upon the concentration and specific gravity of the soil particles and the amount of dispersant added. Each hydrometer measurement at an elapsed time is used to calculate the percentage of particles finer than the diameter given by Stokes’ Law. The series of readings provide the distribution of material mass as a function of particle size. 1.7 This test method does not cover procurement of the sample or processing of the sample prior to obtaining the reduced sample in any detail. It is assumed that the sample is obtained using appropriate methods and is representative of site materials or conditions. It is also assumed that the sample has been processed such that the reduced sample accurately reflects the particle-size distribution (gradation) of this finer fraction of the material. 1.8 Material Processing— Material is tested in the moist or as-received state unless the material is received in an air-dried state. The moist preparation method shall be used to obtain a sedimentation test specimen from the reduced sample. Air-dried preparation is only allowed when the material is received in the air-dried state. The method to be used may be specified by the requesting authority; however, the moist preparation method shall be used for referee testing. 1.9 This test method is not applicable for the following soils: 1.9.1 Soils containing fibrous peat. 1.9.2 Soils containing less than approximately 5 % of fine-grained material ( Note 1 ). 1.9.3 Soils containing extraneous matter, such as organic solvents, oil, asphalt, wood fragments, or similar items ( Note 3 ). Note 3: If extraneous matter, such as wood, can be easily removed by hand, it is permissible to do so. However, there may be cases where the extraneous matter is being evaluated as part of the material and it should not be removed from the material. 1.9.4 Materials that contain cementitious components, such as cement, fly ash, lime, or other stabilization admixtures. 1.10 This test method may not produce consistent test results within and between laboratories for the following soils. To test these soils, this test method must be adapted and these adaptations documented. 1.10.1 Soils that flocculate during sedimentation. Such materials may need to be treated to reduce salinity or alter the pH of the suspension. 1.10.2 Friable soils in which processing changes the gradation of the soil. Typical examples of these soils are some residual soils, most weathered shales, decomposed granites, and some weakly cemented soils. 1.10.3 Soils that will not readily disperse, such as glauconitic clays or some dried plastic clays. 1.11 Samples that are not soils, but are made up of particles may be tested using this method. The applicable sections above should be used in applying this standard. 1.12 Units— The values stated in SI units are to be regarded as standard. Except the sieve designations, they are identified using the “alternative” system in accordance with Practice E11 , such as 3-in. and No. 200, instead of the “standard” designation of 75-mm and 75-µm, respectively. Reporting of test results in units other than SI shall not be regarded as non-conformance with this test method. The use of balances or scales recording pounds of mass (lbm) shall not be regarded as nonconformance with this standard. 1.13 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. 1.13.1 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 this test method to consider significant digits used in analysis methods for engineering or other data. 1.14 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. 1.15 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 Particle-size distribution (gradation) is a descriptive term referring to the proportions by dry mass of a soil distributed over specified particle-size ranges. The gradation curve generated using this method yields the distribution of silt and clay size fractions present in the soil based on size definitions, not mineralogy or Atterberg limit classification. 5.2 Unless the sedimentation sample is representative of the entire sample, the sedimentation results must be combined with a sieve analysis to obtain the complete particle size distribution. 5.3 The clay size fraction is material finer than 2 µm. The clay size fraction is used in combination with the Plasticity Index (Test Methods D4318 ) to compute the activity, which provides an indication of the mineralogy of the clay fraction. 5.4 The gradation of the silt and clay size fractions is an important factor in determining the susceptibility of fine-grained soils to frost action. 5.5 The gradation of a soil is an indicator of engineering properties such as hydraulic conductivity, compressibility, and shear strength. However, soil behavior for engineering and other purposes is dependent upon many factors, such as effective stress, mineral type, structure, plasticity, and geological origin, and cannot be based solely upon gradation. 5.6 Some types of soil require special treatment in order to correctly determine the particle sizes. For example, chemical cementing agents can bond clay particles together and should be treated in an effort to remove the cementing agents when possible. Hydrogen peroxide and moderate heat can digest organics. Hydrochloric acid can remove carbonates by washing and Dithionite-Citrate-Bicarbonate extraction can be used to remove iron oxides. Leaching with test water can be used to reduce salt concentration. All of these treatments, however, add significant time and effort when performing the sedimentation test and are allowable but outside the scope of this test method. 5.7 The size limits of the sedimentation test are from about 100 µm to about 0.1 µm. The length of time required to obtain a stable initial reading on the hydrometer controls the upper range of results, and the test duration controls the lower range. 5.8 The shape and density of the grains are important to the results. Stokes’ Law is assumed to be valid for spherical particles even though fine silt- and clay-sized particles are more likely to be plate-shaped and have greater mineral densities than larger particles. 5.9 High plasticity clays develop structured water layers on their surfaces. According to Zhang and Lu 3 this near surface water can be as dense as 1.4 g/L. This high-density structured water causes an error in this test method and shifts the particle size distribution curve upwards. Correction for the structured water is beyond the scope of this standard but values of percent passing above 100 % are possible and should not be excluded from the report. Note 5: 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.