## 2 Materials and Methods  
### Material  
According to the Australian standard [7], sand sizes range from 2.36 mm to 0.075 mm, with coarse sand ranging from 2.36 to 0.6 mm, medium sand ranging from 0.6 to 0.212 mm, and fine sand ranging from 0.212 to 0.075 mm. Particles larger than 2.36 mm are classified as gravel, while particles smaller than 0.075 mm are classified as silt or clay. Different types of sand were used in the experiments to examine the effect of particle size and shape. The sands used in the study are referred to as L-Sand, M-Sand, P-Sand, and B-Sand.  
For the particle shape impact, four types of sand were used, namely L-Sand, B-Sand, M-Sand, and P-Sand, were each sieved and separated into four different sizes (1.18 to 0.6 mm, 0.6 to 0.425 mm, 0.425 to 0.3 mm, and 0.3 to 0.15 mm). Due to the limitation of the microscope lens, which tends to overlook particles larger than 1.18 mm, only particles below this size were selected.  
To study the impact of particle size, B-sand was sieved and divided into containers based on their size (Figure 1), and five different sands were selected for testing. According to Australian standards [7], four of the selected sands are poorly graded and are considered to be fine sand (B1-Sand) with D\({}_{50}\) of 0.11 mm, low medium sand (B2-Sand) with D\({}_{50}\) of 0.23 mm, high medium sand (B4-Sand) with D\({}_{50}\) of 0.51 mm, and coarse sand (B6-Sand) with D\({}_{50}\) of 1.77 mm. The fifth one is a mixture of sand to create a well-graded sand (B-Sand) with D\({}_{50}\) of 0.58 mm. Therefore, five different sizes were chosen to examine the differences between coarse, medium, and fine sands, as well as to study the effect of poorly graded and well-graded sands.  
Glass beads were utilised to avoid particle shape influence and concentrate only on particle size impact on mechanical behaviour. The glass beads are made of silica mixed with other minerals melted at high temperature to produce a viscous, thick liquid. The liquid is moulded into spherical shapes and hardens as it cools. The regularity of the particle shape of the glass beads, as observed under the microscope, was found to be almost one. The glass beads were separated into two different sizes: GB5 with a D\({}_{50}\) of 0.89 mm and GB6 with a D\({}_{50}\) of 1.77 mm. The specific gravity of the glass beads ranges from 2.45 to 2.50. The specifications of used particulate materials including sand and glass beads are presented in Table 1. The sieve analysis was conducted according to the Australian standard [47], and the results for the used granular material are shown in Figure 2.  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline
**Material** & **Range (mm)** & **Grade** & **C\({}_{\mathbf{u}}\)** & **C\({}_{\mathbf{c}}\)** & **D\({}_{\mathbf{50}\text{(mm)}}\)** & **G\({}_{\mathbf{s}}\)** & **R** & **S** & \(\rho_{\mathbf{r}}\) \\ \hline L5-Sand & 1.18 to 0.6 & PG 1 & 1.44 & 0.96 & 0.89 & 2.65 & 0.288 & 0.589 & 0.439 \\ L4-Sand & 0.6 to 0.425 & PG & 1.20 & 0.97 & 0.51 & 2.68 & 0.421 & 0.546 & 0.484 \\ L3-Sand & 0.425 to 0.3 & PG & 1.20 & 0.97 & 0.36 & 2.69 & 0.302 & 0.591 & 0.447 \\ L2-Sand & 0.3 to 0.15 & PG & 1.45 & 0.96 & 0.23 & 2.74 & 0.288 & 0.578 & 0.433 \\ L1-Sand & 0.15 to 0.075 & PG & 1.45 & 0.96 & 0.11 & - & 0.289 & 0.541 & 0.415 \\ B-Sand & 2.36 to 0.075 & WG 2 & 6.16 & 1.24 & 0.58 & 2.67 & - & - & - \\ \hline \end{tabular}
\end{table}
Table 1: Specifications of the used particulate materials: sand and glass beads.  
Figure 1: The coarse soil (B-sand) is sieved and separated into different containers depending on the granular size.