Soil classification systems, such as the USCS classification, are based on particle size distribution for coarse-grained soils and Atterberg limits for fine-grained soils. Although the classification only requires the particle size distribution to be determined for coarse-grained soils on particles above 0,063 mm, particle size distribution is often measured to better characterise soils in the particle range between 0,002 to 63 mm. Sedimentation methods are used to determine the particle size distribution curve in the range of particles from 0,002 to 0,063 mm, where the variation of the suspension density due to the sedimentation of the particles in suspension is measured. In my thesis I used a standard hydrometer test and a non-standard method with the PARIO device. A hydrometer is a device that measures the average density of the suspension in the area of the hydrometer bulb, while the PARIO device measures the pressure at the depth of the sensor, which depends on the density of the suspension from the sensor to the surface of the water. From the pressure measurements, the particle size distribution curve is then calculated in PARIO Control program, which best fit the pressure measurements. To assess the comparability of the results of the two methods, sedimentation measurements were carried out on 12 different materials, with measurements conducted on two test specimens for each method. This allows us to assess the repeatability and accuracy of the measurements. In addition, measurements were made on a mixture of rock flour and karst clay. It was found that particle size distribution curve measured in the PARIO device and the hydrometer are similar but often shifted. The most common errors were results of poor quality of specimen mixing, hydrometer oscillations, homogeneity of the soil sample, as well as random measurement errors. Despite some advantages of the PARIO device, it was found that the grain size distributions measured with the hydrometer are more repeatable than those measured with the PARIO device.
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