## 3 Results
### Numerical Simulation of Uniaxial Compression Test with FLAC3D  
When the pre-processing of the SRM models is completed, the data of models is going to be imported into FLAC3D to simulate the uniaxial compression test. Some key physical and mechanical parameters of the soil and rock are shown in Table 2. In SRMs, the mechanical characteristics of the rock block, matrix, and BMI are often quite complicated. The rock block is typically the strongest and has a strength ratio to the matrix that is at least larger than two [38]. The matrix is stronger than the junction of the block and matrix but has a lower compression strength than the rock block. When considering the BMI in unwelded SRMs, the strength ratio to the matrix is frequently less than one [39]. Most current studies ignore BMI in SRMs. Evidently, both the presence and strength of the BMI have a great influence on the mechanical properties and failure mode of the SRMs. Due to the lack of relevant parameters in this regard, this paper refers to concrete with similar structure and properties of the SRMs [40]. In concrete, the strength of the interfacial transition zone (ITZ) is usually 0.1-0.9 of the matrix [41]. Therefore, to simulate the cementation properties of the BMI, this paper applied one fifth of the strength parameters of soil to BMI. The result of this numerical simulation is compared with the experimentally obtained UCS value [14]. Meanwhile, the corresponding stress-strain curve is investigated to validate the accuracy and reliability of the simulation in this paper. As shown in the stress-strain curve (Figure 7), the stress-strain curve of numerical simulation is in a good agreement with that of the experimental test, especially in the pre-peak stage. The result clearly indicates that the method in this paper can make a rather reasonable simulation of the mechanical properties of the SRMs under uniaxial compression. In this paper, five SRM models with a 5% increase in VBP from 50% to 70% each were used for the numerical simulation of uniaxial compression tests. In order to avoid the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Composition** & \begin{tabular}{c} **Young Modulus** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Poisson** \\ **Ratio** \\ \end{tabular} & \
\begin{tabular}{c} **Cohesion** \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Friction Angle** \\ **(\({}^{\circ}\))** \\ \end{tabular} \\ \hline Rock block & 1320 & 0.22 & / & / \\ Matrix & 402 & 0.32 & 16.5 & 22.64 \\ Block-matrix interface & 80.4 & 0.064 & 3.3 & 4.528 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material parameters of mesoscale concrete model. Figure 7: Stress–strain curves from the experiment and the numerical simulation. influence of mechanical parameters on the numerical simulation results, a pure matrix model consisting of soil was generated separately, and a uniaxial compression test was performed to obtain the UCS value of the pure matrix model. Then, this paper utilized the ratio of the UCS value of the SRM model to the UCS value of the pure matrix model to describe the uniaxial compressive strength of the SRM. An overall declining relationship between the UCS of the SRMs and VBP can be evidently observed from the results. This declining trend can better demonstrate the influence of VBP on uniaxial compressive strength of unwelded SRMs in experiment conducted by [PERSON] et al. [14], as shown in Figure 8. However, the decrease in UCS value with VBP from 50% to 55% is relatively flat, then, the UCS value will decrease relatively quickly with a similar trend as the VBP increases. This phenomenon can be explained by the fourth rule related to the relationship between the strength and VBP, which was summarized by [PERSON] et al. [42]. As described by the fourth rule, between VBP = 0% and VBP = 100%, the UCS\({}_{\text{SRM}}\) drops from the UCS\({}_{\text{matrix}}\) to zero since interlocking contact between blocks is unquestionably believed to be nearly nonexistent or extremely low for VBP > 60%.