1.1 This test method covers the quantitative determination of the distribution of particle sizes in soils. The distribution of particle sizes larger than 75 m (retained on the No. 200 sieve) is determined by sieving, while a sedimentation process, uses a hydrometer to determine the distribution of particle sizes smaller than 75 m. 1.2 Hydrometer analysis is based on Stokes law, which relates the terminal velocity of a free-falling sphere in a liquid to its diameter. It is assumed that Stokes law can be applied to a mass of dispersed soil particles of various shapes and sizes. Larger particles settle rapidly relative to smaller ones. The hydrometer analysis is an application of Stokes law that permits the calculation of the grain size distribution in silts and clays in which the soil particles are given the sizes of equivalent spherical particles. The density of a soil-water suspension depends upon the concentration and specific gravity of the soil particles. If the suspension is allowed to stand, the particles will gradually settle out of the suspension decreasing the density of the soil suspension. The hydrometer is the instrument used to measure the density of the suspension at a known depth below the surface. The density measurement, together with knowledge of the soil particle specific gravity, determines the percentage of dispersed soil particles in suspension at the time and depth of measurement. Stokes law is used to calculate the maximum equivalent particle diameter for the material in suspension at the measured depth and for the elapsed time of settlement. A series of measurements at these elapsed times are used to calculate the percentages of particles finer than the diameters given by Stokes law. This series of readings will reflect the amount of different size particles in the fine-grained soils. 1.3 Two test methods are provided in this standard, Method A and Method B. The method used may be specified by the requesting authority; otherwise Method B is to be used. 1.3.1 Method A--Hydrometer Only 1.3.2 Method B--Combined Sieve and Hydrometer 1.4 Sample Processing--Dry preparation or wet preparation may be used to process the sample. The wet preparation method shall be the referee method. Refer to 9.1 for dry and 9.2 for wet preparation methods. 1.5 This test method does not cover procurement of the sample. It is assumed that the sample is obtained using appropriate methods and is representative of site materials or conditions or both. 1.6 This test method is not applicable for the following soils: 188.8.131.52 Soils containing fibrous peat that will change in particle size during the drying, washing, or sieving process. 184.108.40.206 Soils containing extraneous matter, such as organic solvents, oil, asphalt, wood fragments, or similar items. Such extraneous matter can affect the washing and sieving processes. 220.127.116.11 Materials that contain cementitious components, such as cement, fly ash, lime, or other stabilization admixtures. 18.104.22.168 Friable soils that 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. 22.214.171.124 Soils that will not readily disperse such as glauconitic clays or some dried plastic clays. 1.7 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D 6026 unless superseded by this test method. 1.7.1 The procedures used to specify how data are collected/recorded and calculated in these test methods 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 this test method to consider significant digits used in analysis methods for engineering design. 1.8 Units--The dimensional values stated in either SI units or inch-pound units are to be regarded as standard, such as 200-mm or 8-in. diameter sieve. Except, the sieve designations are typically identified using the alternative system in accordance with Practice E 11, such as 3 in. and No. 200, instead of the standard system of 75 mm and 75 m, respectively. Only SI units are used for mass determinations, calculations, and reported results; however, the use of balances or scales recording mass (lbf) shall not be regarded as nonconformance with this standard. 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.
The existing hydrometer standard D 422 possibly causes degradation of material as it is processed. This proposed method will eliminate the degradation.
Keywordsgrain size; hydrometer analysis; hygroscopic moisture; particle-size; sieve analysis
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top