ASTM WK11776

    New Test Methods for Particle Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis

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    Developed by Subcommittee: D18.03 | Committee D18 | Contact Staff Manager



    WK11776

    1. Scope

    1.1 This test method covers the quantitative determination of the distribution of particle sizes of the fine-grained portion of soils. The sedimentation or hydrometer method is used to determine the particle-size distribution (gradation) of the material that is finer than the No. 200 (75-um) sieve and larger than about 0.2-um. The test is performed on material that passes the No. 10 (2.0-mm) or finer sieve and results are presented as a percent of the mass of the maximum particle size used for the sedimentation test specimen. 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 a sieve analysis resulting in 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 1The 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 silts and clays, and therefore should not be tested with this method. 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 Method D6913 (Note 2). NOTE 2Subcommittee 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 is the 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 separated by size in both time and position within 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. 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 bulk sample or processing of the bulk sample prior to obtaining the reduced sample in any detail. It is assumed that the bulk sample is obtained using appropriate methods and is representative of site materials or conditions. It is also assumed that the bulk sample has been processed such that the reduced sample accurately reflects the particle-size distribution (gradation) of this finer fraction of the bulk material. 1.8 Material Processing-Two preparation methods, moist and air-dried, are provided to obtain a sedimentation test specimen from the reduced sample. The method selected will depend on the type of sample, the range of particle sizes, the initial conditions of the material, the plasticity of the material, and the need for other testing of the material. The method to be used may be specified by the requesting authority; however, the moist preparation method shall be the referee procedure. 1.9 This test method is not applicable for the following soils: 1.9.1 Soils containing fibrous peat. 1.9.2 Soils containing extraneous matter, such as organic solvents, oil, asphalt, wood fragments, or similar items. 1.9.3 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 or altered and these alterations documented. 1.10.1 Soils which 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 the sieving processes change the gradation of the soil. Typical examples of these soils are some residual soils, most weathered shales, and some weakly cemented soils, such as hardpan, caliche or coquina. 1.10.3 Soils that will not readily disperse, such as glauconitic clays or some dried plastic clays. 1.11 Some materials 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 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. 1.12.1 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 users 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. 1.13 Units-The values stated in SI units are to be regarded as standard. Except, the sieve designations are typically identified using the alternative system in accordance with Practice E11, such as 3-in. and No. 200, instead of the standard of 75-mm and 75-m, 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.

    D422 combines both the hydrometer and sieving methods into one standard and there is not a method if a user only needs to perform a hydrometer analysis. There are times when only a sedimentation (hydrometer) analysis is needed or requested on a specimen. This standard provides the needed guidance on how to perform a sedimentation (hydrometer) analysis independent of any sieving. Once approved, this standard along with D6913 and the simplified combo standard, will provide users with appropriate guidance when it comes to deciding which standard theyll need to follow based on the test specimen and the requested analysis needed.


    Keywords

    clay; silt; grain size; hydrometer analysis; sedimentation analysis; particle-size distribution (gradation); sieve analysis

    The title and scope are in draft form and are under development within this ASTM Committee.

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    Work Item Status

    Date Initiated:
    6-19-2006

    Technical Contact:
    Kendra Adams

    Item:
    002

    Ballot:
    D18 (14-01)

    Status:
    Negative Votes Need Resolution