Metrological Aspects of Studying the Particle Size Distribution of Soils according to the Kachinskii Method

Abstract—

Particle size distribution (PSD) of a significant number of soil samples of various geneses from the Komi Republic was studied by the Kachinskii method (KM). Calculated, procedural, random, and systematic factors influencing the precision and correctness of measurement results performed with the KM protocol are considered. The influence of sample preparation (the degree of grinding of soil samples) and procedures for measuring the mass fraction of elementary soil particles (ESPs) on the quality of the results of studying soil PSD was assessed. The instability of measuring the mass of fine sand (0.05–0.25 mm) and coarse silt (0.01–0.05 mm) fractions with the KM protocol was shown. The dependence of the uncertainty of measurement results caused by random factors on the mass fraction of ESPs of particular size fractions is noted: the lower the mass of ESPs in the fraction, the higher the uncertainty of the measurement results. A modification of the Kachinskii method (KM) has been developed to improve the quality of soil PSD analysis. It includes: (1) separation of fine sand particles using a sieve with a mesh size of 0.05 mm (instead of calculating this fraction by difference according to the MK protocol); (2) use of scales of the first class of accuracy to measure the mass fraction of silt and clay particles; (3) control of the PSD research based on the summation of the measured values of the mass fraction of ESPs of six fractions and acid-soluble compounds (losses from HCl treatment). The standard for operational control of the mass fraction of the sum of ESPs after dividing them into fractions is 100 ± 5%. A metrological study of the Kachinskii method and its modifications was carried out. The proposed modification of Kachinskii`s method made it possible to reduce the uncertainty in the measurement results of the mass fraction of ESPs of small fractions (ω_n < 10%) and shift the lower limit of measurements to 1%.