## 5 Influencing Factors of Strength Responses of Soil-Rock Mixture  
In accordance with the methodology for determining strength in the uniaxial compression test on rock, the peak strength of the axial stress-strain curve of soil-rock mixture is identified as the UCS value. The UCS values for soil-rock mixtures with varying rock contents, derived from computer numerical simulations, are presented in Table 6. The results demonstrate that as rock content increases from 0 to 30%, the UCS exhibits a rapid exponential decline, decreasing from 923.62 kPa to 407.67 kPa. Correspondingly, the axial strain at which UCS occurs also decreases, from 3.29% to 2.03%. Figure 12: Force chain distributions of soil–rock mixture with a friction coefficient of (**a**) 0.9, (**b**) 0.5, (**c**) 0.3, and (**d**) 0.1 under the uniaxial compression condition. The discussions above show that underlying cause of the decrease in strength of soil-rock mixture triggered by an increase in rock content is the emergence of weak-strength soil-rock contact surfaces. Figure 13 illustrates the variation in UCS of soil-rock mixture models with varying rock contents under various friction coefficients of soil-rock contact. The results indicate that the UCS consistently declines as the friction coefficient decreases under different rock content conditions. Additionally, the sensitivity of UCS to variations in the friction coefficient varies significantly with different rock contents. Under conditions of low rock content (5%), the UCS decreases from 947.56 to 842.43 kPa, representing a reduction of 11.09% as the interface friction coefficient decreases from 0.9 to 0. Conversely, at the rock content of 30%, the UCS decreases from 417.63 kPa to 243.37 kPa, reflecting a substantial reduction of 41.73% as the friction coefficient decreases. The variation trends of UCS indicate that both rock content and soil-rock interface strength significantly influence UCS. From the perspective of material stiffness, the increase in rock content facilitates a gradual transition in the mechanical properties of soil-rock mixture from those of soil to those of a jointed rock mass, resulting in enhanced material stiffness. To quantitatively assess the influence of rock content and soil-rock interface strength on UCS, this paper discusses the disturbance effect of rock content by considering how rock blocks damage the initial structure of the soil matrix. The strength disturbance ratio (\(\sigma_{\text{S-RM}}/\sigma_{\text{c}}\)) is defined as the ratio of UCS between the soil-rock mixture and the soil matrix. Figure 14 presents the variation in the strength disturbance ratio of UCS with rock content of soil-rock mixture under varying friction coefficients. An exponential function of the form y = A \(\times\) Bx was used to fit the UCS variation, and the resulting estimated formulae for UCS of soil-rock mixture are shown in Figure 14. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Rock Content/(\%)** & **UCS/(kPa)** & **Axial Strain Corresponding to UCS/\%** \\ \hline
0 & 923.62 & 3.29 \\
5 & 853.66 & 3.11 \\
10 & 700.02 & 2.64 \\
15 & 665.97 & 2.67 \\
20 & 634.80 & 2.64 \\
25 & 522.59 & 2.27 \\
30 & 407.67 & 2.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: UCS values of soil–rock mixtures with varying rock contents based on the computer simulation. Figure 13: Relationship between UCS and interface friction coefficient of soil–rock mixtures with varying rock contents. Figure 15 presents the relationship curves between the parameter A and B in the estimation formula and the friction coefficient of the interface. The results reveal clear functional relationships between these undetermined parameters and friction coefficient, as follows:  
\[A=-0.249\mu^{2}+0.222\mu+1.216 \tag{3}\]  
\[B=0.969-0.017\times 0.025^{\mu} \tag{4}\]  
The results in Figure 15 demonstrate that as the friction coefficient of the interface increases, the parameter A exhibits a parabolic trend, and the values of parameter A are relatively close.