## 3 Results  
The aggregate characteristics as measured for the reference samples are shown in Table 1. The small-sized sample (63-250 \(\upmu\)m) contains the largest amount of clay and the lowest amount of sand. The lowest amount of clay was found in the reference sample of 500-1000 \(\upmu\)m. Sample 63-250 shows a similar composition of clay, silt, and sand to that of the bulk sample. The other two samples are different from the bulk sample when a lower percentage of clay and silt and a higher percentage of sand exist compared with the bulk sample. Studies have shown that there is a connection between the content of clay and the aggregate size in different soils. The aggregate size increased with higher clay contents [35; 36]. Contrary to expectations, the results in the present experiment show an opposite trend in which the smaller aggregates contain more clay and silt than the larger ones. The amount of soil organic matter (SOM) was found to be at the same level (2.1-2.2%) for all the soil samples (Table 1). The SOM of the bulk sample (2.91%) is somewhat higher than the SOM of the fraction samples. We may expect that a high content of SOM is found in aggregates larger than 2000 \(\upmu\)m. The content of the carbonate was relatively higher in samples of 63-250 \(\upmu\)m and 250-500 \(\upmu\)m, compared with the content (8.5%) of the 500-1000 \(\upmu\)m. The carbonate content is also contributing to the production of larger aggregates [1; 37]. According to the present results, there is an opposite trend, when the large aggregates (500-1000 \(\upmu\)m) contain less carbonate than the small ones. The wind velocities were measured at several heights above the tunnel bed in each fan frequency to determine the wind profile in the tunnel (Figure 2). In all fan frequencies tested, the wind velocity increases as the height above the tunnel bed increases. The data show a high positive correlation (R\({}^{2}\) = 0.98) between the fan frequency and the wind velocity at height 0.2 m. The wind velocity at height above 0.2 m starts to decrease because of the wall effect at the roof of the tunnel. The changes in the wind velocity with height allows the calculation of the shear velocity (u*). The shear velocity in this experiment ranged from 0.24 m/s to 0.52 m/s. A strong positive correlation (R\({}^{2}\) = 0.98) between the shear velocity and the fan frequency was found (Figure 2). \begin{table}
\begin{tabular}{c c c c c} \hline  & **Clay (\%)** & **Silt (\%)** & **Sand (\%)** & **CaCO3 (\%)** & **SOM (\%)** \\ \hline
63–250 \(\upmu\)m & 16.1 (6.0) & 60.5 (12.3) & 23.3 (18.4) & 14.4 (1.6) & 2.2 (0.1) \\ \hline
250–500 \(\upmu\)m & 12.8 (1.5) & 53.1 (4.2) & 34.0 (5.7) & 12.9 (0.8) & 2.1 (0.2) \\ \hline
500–1000 \(\upmu\)m & 11.7 (0.8) & 55.6 (1.2) & 32.6 (0.3) & 8.5 (1.5) & 2.1 (0.3) \\ \hline Bulk sample & 13.7 (N/A) & 60.4 (N/A) & 25.8 (N/A) & 10.6 (0.7) & 2.9 (0.0) \\ \hline \end{tabular}
\end{table} 
Table 1: Mean values of soil properties for the reference samples and the bulk sample. Figure 2: (**a**) Wind velocity (m/s) measured at different heights above the tunnel bed (z) under different fan frequencies (Hz) (**b**) Correlation between the fan frequencies applied in the wind tunnel and the calculated shear velocity. Figure 3 shows the results of the saltation measurements as weighed from the traps at different shear velocities. The results show that the range of saltation values is not uniform across all samples. In sample 63-250 \(\upmu\)m the lowest value is 0.1 g and the highest is about 100 time more (10.1 g). The highest value however was recorded at 0.43 m/s. The material analysis of the saltation mass (Table 2) showed only a small amount (11.8%) of material that is \(<\)63 \(\upmu\)m at velocity 0.52 m/s (Table 2). This may explain a decline of about 30% in the saltation mass of 0.52 m/s, compared with 0.43 m/s, in which the stronger wind entered more particle into suspension (dust-PM) rather than in saltation. In sample 250-500 \(\upmu\)m the lowest value is 0.07 g and the highest is about 200 time more (14 g).