## 3 Meso Analysis of Mechanical Characteristics of Soil-Rock Mixture
### Calibration of the Meso-Parameter  
To characterize the differences in mechanical properties between real soil and rock particles, as well as the structural heterogeneity of soil-rock mixture, contact bond strength models with varying meso-parameters were calibrated. The parameter calibration was primarily conducted using the trial-error method to ensure the simulation results closely aligned with the experimental results, ultimately obtaining a group of representative meso-parameters. First, the meso-parameters of the bond contact model between soil-soil particles were calibrated based on the experimental results of the pure soil specimen (with a rock content of 0). Next, the meso-parameters of the rock-rock and soil-rock contact models were calibrated using the experimental results of the soil-rock mixture with 30% rock content. Consequently, all meso-parameters of different types of particle-particles and particle-wall were obtained, as listed in Table 5.  
During the simulation process, the walls on both sides of the model were first removed, transitioning the simulation condition to uniaxial compression. The axial loading speed of the wall was then set to 0.005 m/s, and the uniaxial compression simulation test of soil-rock mixture was performed. The test was terminated when the post-peak axial stress dropped to 0.7 times the peak strength. The simulation results of soil-rock mixture with varying rock contents are presented in Figure 10. The results demonstrate that, for the same rock content and specimen size, the axial stress-strain curves obtained from the simulations closely resemble experimental results, exhibiting a clear linear increase followed by strain-softening behavior. Despite some discrepancies between the simulation and experimental results (such as the strain corresponding to the peak strength), the relative error values of the UCS are within 10%. This suggests that the meso-structure model of soil-rock mixture with irregular rock blocks generated in this study can more accurately reflect the real structure and mechanical characteristics of the soil-rock mixture.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Contact Type**} & **Contact Name** & \begin{tabular}{c} **Contact Normal** \\ **Stiffness,** \\ \(\mathbf{k_{n}}\)**/(N\(\cdot\cdot\)m\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Normal-to-** \\ **Shear Stiffness** \\ **Ratio, \(\mathbf{k_{n}}\)**/**\(\mathbf{k_{s}}\)** \\ \end{tabular} & \begin{tabular}{c} **Shear Strength,** \\ \(\mathbf{F_{n}}^{c}\) \\ \end{tabular} & \begin{tabular}{c} **Tensile** \\ **Strength, \(\mathbf{F_{s}}^{c}\)** \\ \end{tabular} & \
\begin{tabular}{c} **Friction** \\ **Coefficient, \(\mu\)** \\ \end{tabular} \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Particle- \\ particle \\ \end{tabular} } & Soil–soil & \(3.0\times 10^{7}\) & 1 & 1100 & 900 & 0.3 \\  & Rock–rock & \(3.5\times 10^{7}\) & 1 & 500 & 500 & 0.9 \\  & Soil–rock & \(3.0\times 10^{7}\) & 0.5 & 1000 & 800 & 0.7 \\ \hline \multirow{2}{*}{Particle–wall} & Soil–wall & \(1\times 10^{7}\) & 0.0 & — & — & — \\  & Rock–wall & \(6.5\times 10^{7}\) & 0.0 & — & — & — \\ \hline \hline \end{tabular}
\end{table}
Table 5: Meso-parameters of the soil mixture numerical model.