## 3 Analysis of Experimental Results
### Hysteresis Loop Area and Damping Ratio  
After processing the test data based on Figure 4 and Equation (3), we have the hysteresis loop area, \(S\), of the soil samples under 500 kPa of vertical pressure (Table 2). The distribution of the hysteresis loop area, \(S\), and damping ratio, \(\lambda\), are shown in Figures 7 and 8.  
It can be observed from Table 2 and Figure 7 that under the same number of reciprocating shears, the hysteresis loop area of the soil samples is significantly affected by the soil fabric characteristics, and the hysteresis loop area of the soil samples increases as the coarse grain content increases. When the number of reciprocating shears is \(N=1\), for example, the hysteresis loop area, \(S\), increases by 10.85%, 9.92%, and 19.73% as \(P_{5}\) increases from 27.56% to 75.43%. The reason is that during the shearing process, the soil will produce energy loss due to overcoming the friction resistance, and the area of the hysteresis loop can be used to characterize the energy loss. As the number of coarse gra  
Figure 6: Reciprocating shear strength distribution map.  
increases, the contact and interlocking among the soil grains increases, and the external force required to induce shear deformation gradually increases. As a result, the energy loss of the soil sample to overcome the friction between the block grains also gradually increases, manifested as the increase of the hysteresis loop area.  
At the same coarse grain content, the hysteresis loop area of the soil samples gradually decreases with the number of reciprocating shears. Taking \(P_{5}=27.56\%\) as an example, the decrease in the hysteresis loop area is 23.41%, 17.82%, and 16.12% when the number of reciprocal shears increases from \(N=1\) to \(N=4\). Among them, the decrease is larger from \(N=1\) to \(N=2\), and those during other shears are less significant. The possible reason is as follows. On the one hand, the contact and interlocking among the block grains on the shear surface are intense during the first reciprocating shear of the soil sample, and the frictional resistance is large. Therefore, the energy loss to overcome the frictional resistance is greater upon the shear failure of the soil sample, leading to larger hysteresis loop areas. On the other hand, as the number of reciprocating shears on the soil samples increases, the block  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number of** **Shears N/Times**} & \multicolumn{4}{c}{**Hysteresis Loop Area 5/kPa-mm**} \\ \cline{2-5}  & \(P_{5}\) = **27.56\%** & \(P_{5}\) = **38.02\%** & \(P_{5}\) = **61.34\%** & \(P_{5}\) = **75.43\%** \\ \hline
1 & 21,651 & 24,000 & 26,380 & 31,586 \\
2 & 16,583 & 18,537 & 21,885 & 24,934 \\
3 & 13,628 & 16,022 & 19,055 & 21,881 \\
4 & 11,431 & 13,815 & 17,003 & 18,912 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Grain size distribution of argillaceous siltstone rockfill materials from the 1980 m dumping terrace.  
Figure 8: Damping ratio distribution diagram.  
Figure 7: Hysteresis loop area distribution map.  
grains on the shear surface are relatively loose, due to the previous shear deformation, and gradually rounded. In the meantime, grain fragmentation reduces the grain size and weakens the interlocking, and the roughness of the shear surface decreases. In turn, the energy loss to overcome the frictional resistance of the soil grains upon shear failure of the soil sample is reduced. Therefore, the decrease in the hysteresis loop area is greater during the second reciprocating shear, and the decrease becomes slower with the number of reciprocating shears.  
As shown in Figure 8, the damping ratios of the soil samples all tend to decrease with the number of reciprocating shears at the same coarse grain content. With the same number of reciprocating shears on the soil samples, the correlation between the damping ratio and coarse grain content is not significant, i.e., the damping ratio is not related to the coarse grain content.