Comparison of laser diffraction method and hydrometer method for soil particle size distribution analysis

Abstract The article aims to present a comparative study of two methods used to determine the particle size distribution of fine and medium coarse soils. These methods are used to determine the grain size distribution curve in practice; however, for different purposes. The classical sedimentation method, based on the Stoke’s sedimentation law (hydrometer, areometric, the Casagrande’s method), standardized for a geotechnical classification of soils was compared with the laser diffraction method on the Mastersizer 3,000 analyser used for soil science purposes. The first comparison on nine samples showed significant differences, especially for larger fractions above 0.01 mm. All measured values of falls from laser diffraction analysis (LDA) showed higher values of all analysed fractions. It was also interesting to follow the trend between the tests for the preparation of conversion factors. The analysis also outlined the direction for further comparison. For the geotechnical use of the LDA, it will be necessary to take into account the sample preparation and processing before analysis.