## 1 Introduction

Table 1: Summary of the total number of scientific papers (research and review article, book chapter, conference paper) using “Hopkinson bar” as a keyword concerning dynamic experiments with samples of different materials from 2018 to 2022 according to the resources of the scientific databases Web of Science and Springer Link [26; 27]. Testing the grain size distribution of non-cohesive soils is carried out by determining the granulometric composition using the laboratory sieve method according to [44]. The smallest mesh diameter of the sieve is 0.063 mm (63 \(\upmu\)m)-in order to gain a more accurate understanding of the further course of the grain size curve in the range below 63 \(\upmu\)m, it is necessary to use precision laboratory equipment, as aerometric analysis for small soil samples is not feasible. In this study, a laser particle size analyzer was used to produce a more detailed grain size curve from a grain size of 0.01 \(\upmu\)m to 3500 \(\upmu\)m--additional grain size curve data in the range of 0.01-63 \(\upmu\)m can be obtained in comparison with classic sieve analysis (gradation test). Sand, as a natural granular material, is a complex non-equilibrium energy dissipating system requiring detailed analyses. This is the motivation of the authors of the manuscript to add to the wide area of already existing publications on different sands the results of dynamic studies for one type of sand-silty sand (there is still a space of insufficiently studied examples of these soils). The aim of this study was to investigate the change in the granulometric composition of silty sand (two soil types--\(f_{Si+C,1}=15.14\%\) and \(f_{Si+C,1,2}=20.48\%\)) in dynamic SHPB experiments with varying moisture content--\(w_{1}=0\%\), \(w_{2}=5\%\), \(w_{3}=10\%\) and \(w_{4}=15\%\)--and the impact velocity of the loading bar projectile for SHPB pneumatic launcher pressures--\(p_{1}=1.2\) bar (\(v_{1}=12.76\) m/s), \(p_{2}=1.8\) bar (\(v_{2}=17.69\) m/s), and \(p_{3}=2.4\) bar (\(v_{3}=21.32\) m/s). Major points of highlights and innovations of study in this paper:  
* Use of laser particle size analyzer to determine the grain size composition of the soil sample (grain size curve)--a more accurate method due to the wide range of possibilities for 0.01 \(\upmu\)m to 3500 \(\upmu\)m grain diameters testing compared to classic sieve analysis (gradation test) and aerometric analysis methods. * Two types of silty sand with different contents of fine fractions were used for the study--\(f_{Si+C,1,2}=15.14\%\) and \(f_{Si+C,1,2}=20.48\%\). The manuscript also has a practical (not only academic) aspect because the two types of silty sand studied were from the construction site of two different construction critical infrastructure facilities in Poland--the soil samples taken were really existing in the subsoil. * The study was conducted for a number of variants of soil samples depending on the variables, the impact velocity of the loading bar projectile for SHPB pneumatic launcher pressures, and moisture content of the sample (below and above the optimum moisture content) in order to create several potential sets of conditions for the use of this soil as, for example, ground protection layers loaded by dynamic action. * Repeatable trends in changes in the granulometric composition of soil samples were observed and shown graphically on grain size curves. The largest percentage change in granulometric composition through an increase in the value of the silt and clay fraction relative to the reference sample \(f_{Si+C}\) for both types of silty sand tested occurs for the same moisture content variant \(w_{2}=5\%\)--for soil \(f_{Si+C,1,1}=15.14\%\), there is an increase in the fine fraction of 11.08%, and for soil\(f_{Si+C,2}=20.48\%\), there is an increase in the fine fraction of 15.17%.