## 3 Analysis of Experimental Results
### Analysis of Shear Strength Parameter  
As a common type of slope in geotechnical engineering, the shear strength parameter of dumping field slopes is an important index for analyzing and evaluating their stability. The experimental data are compiled according to Figure 6. The forward shear strength during each reciprocating shear is taken as the failure shear strength of that reciprocating shear, which is fitted with different normal stresses according to the Coulomb equation expressed in Equation (4). The fitting process is shown in Figure 9. The fitting results are shown in Table 3. How the cohesion and internal friction angle of the argillaceous siltstone rockfill material relate to the coarse grain content and the number of reciprocating shears is depicted in Figure 10.  
\[\tau=\sigma\tan\varphi+c \tag{4}\]  
where \(\tau\) is the soil shear strength (kPa); \(\sigma\) is the normal stress (kPa); \(\varphi\) is the internal friction angle of the soil (\({}^{\circ}\)); \(c\) is the soil cohesion (kPa). Figure 9: Rockfill shear strength parameter fitting diagram. As shown in Figure 10, the cohesion and internal friction angle of the argillaceous siltstone rockfill material are positively correlated with the coarse grain content during the reciprocating shear, and they both gradually increase with the coarse grain content. Taking the first reciprocating shear as an example, the cohesion increases by 10.14% from 34.5 kPa to 38 kPa as the coarse grain content increases from \(P_{5}=27.56\%\) to \(P_{5}=75.43\%\), and the internal friction angle increases by 34.60% from 31.68\({}^{\circ}\) to 42.64\({}^{\circ}\). The main reason is as follows. At low coarse grain contents, the contact and interlocking among the soil grains of the rockfill material are not sufficient, and the soil grains are in suspension, with weak interlocking. With the increase of the coarse grain content, the block grains increase. The coarse-fine grain contact and interlocking are sufficient and stronger, and the shear stress required for soil shear failure gradually increases. Accordingly, the cohesion and internal friction angle gradually increase. Figure 10 also shows that the cohesion and internal friction angle of the argillaceous siltstone rockfill material are negatively correlated with the number of reciprocating shears, and they both gradually decrease with the number of reciprocating shears. Taking the coarse grain content \(P_{5}=27.56\%\) as an example, the cohesion decreases by 4.35%, 3.03%, and 1.56% with the number of reciprocating shears, and the internal friction angle decreases by 12.28%, 8.71%, and 11.35%, respectively. The reason is as follows. During the first reciprocating  
Figure 10: The relationship of shear strength parameters with coarse grain content and shear times. (**a**) Internal friction angle; (**b**) cohesion. \begin{table}
\begin{tabular}{c c c c} \hline
**Coarse Grain** & **Number of Reciprocating** & **Cohesion _c_/kPa** & **Internal Friction** \\
**Content**\(P_{5}\)**/\%** & **Shears N/Time** & **Angle _q\({}^{c}\)_ & **Angle _q\({}^{c}\)_ \\ \hline  & 1 & 34.50 & 31.68 \\
27.56 & 2 & 33.00 & 27.79 \\  & 3 & 32.00 & 25.37 \\  & 4 & 31.50 & 22.49 \\ \hline  & 1 & 36.00 & 35.37 \\
38.02 & 2 & 35.00 & 31.92 \\  & 3 & 34.00 & 29.50 \\  & 4 & 33.50 & 27.60 \\ \hline  & 1 & 37.50 & 37.95 \\
61.34 & 2 & 36.00 & 35.61 \\  & 3 & 35.00 & 33.68 \\  & 4 & 34.50 & 31.55 \\ \hline  & 1 & 38.00 & 42.64 \\
75.43 & 2 & 36.50 & 40.80 \\  & 3 & 35.50 & 38.63 \\  & 4 & 35.00 & 36.48 \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of how the shear strength parameter relates to coarse grain content and the number of reciprocating shears. shear, the contact among the soil grains is close, with sufficient interlocking, leading to the greater shear stress required for soil shear failure. Accordingly, the cohesion and internal friction angle are greater. As the number of reciprocating shears increases, the spatial structure of the soil grains on the shear surface is disturbed and destroyed.