## 3 Results and Discussion  
The samples of local organic soils representing the full range of classifications, i.e., low-organic, medium-organic and high-organic soils, were selected to determine the particle size distribution. As some the samples were collected in person and others were supplied in varying quantities by co-operating geotechnical contractors from sites of current projects, their availability and quantity were limited in some cases, which was reflected in the number of tests carried out. The main objective of this review was to determine the granulometric composition of organic soils using laser diffraction, which appears to be the best method in this case due to the minimal impact on the structure of the soil at the preparation stage. Organic soils have an exceptionally complex structure, as they are mostly composed of mineral-organic aggregates, which are very sensitive to damage and require different methods than those that have proven effective for non-plastic (e.g., sand, gravel) and plastic minerals soils (e.g., silt, clay). It should be noted that the grains were classified as clay, silt and sand fractions, but these are conventional terms that refer only to the grain size range of the fraction, and not to the type of soil. Thus, the \"clay fraction\" was assigned mineral-organic aggregates up to 0.002 mm, the \"silt fraction\" from 0.002 mm to 0.05 mm and the \"sand fraction\" from 0.05 mm to 2 mm [1,2]. The situation is further complicated by the fact that currently, the specialist literature lacks practical guidelines on conducting and interpreting organic soil research using the laser diffraction method; therefore, the presented results and methods of their interpretation are, in a way, pioneering and open to further discussion. Two types of laser diffractometers (Analysette 22 and Helos) were used for this research, characterized by different types of sample dispersion and measurement methods, which are described in detail in Section 2.2. This allowed for a comparison of results that theoretically should have been similar. Although the laser diffractometer method has long been known and used in various aspects of geotechnical research, it is not considered a leading method, mainly due to the difficulty of relating the results to methods recognized as standard. The results of all studies were considered from different angles, giving them a multi-dimensional character, and were addressed in the following manners:  
* Individually, via independent reference to each test method separately (Section 3.1), where the percentage of individual fractions in a given sample was analyzed and attempts were made to determine the regularity (tendency) of the occurrence of individual fractions, e.g., whether the fraction proportions are always the same or whether one fraction is always dominant, of course, within a given classification group, e.g., highly organic soils. * Collectively, with reference to all research methods used simultaneously (Section 3.2), where the percentages of the three main fractions obtained by laser diffractometers and the hydrometric method were compared within each sample separately and additionally in comparison with the remaining samples of a given classification group. \begin{table}
\begin{tabular}{c c} \hline \hline
**System** & \\ \hline Instrument & HELOS (H3324) and QUXEL, R3 + R7 \\ Software & PAQXOS 5.1.1 \\ \hline Dispersing Method & \\ \hline Dispersant & Water \\ Cuvette size & 2 mm \\ Fill level & High \\ Temperature & 20 \({}^{\circ}\)C \\ Sonication & 60 s at 100\% power, 30 s pause \\ Pump speed & 1000 rpm \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Details of the measurement conditions using a laser diffractometer. * Individually, in terms of the considered grain size, i.e., within a given fraction (Section 3.3), determined by three independent research methods for all samples in a given series of tests.