## 2 Numerical Model Validation
### Material Constitutive Model and Parameters  
The backfill and foundation soil were simulated using the Mohr-Coulomb model. Table 1 presents the input parameters for the soil model. The parameter values were the same as those used by [PERSON] and [PERSON] (2014) [10] and [PERSON] et al. (2016) [41]. The backfill friction angle of 54\({}^{\circ}\) was determined from the triaxial shear-strength parameters using a plane-strain friction angle calculation method [42]. The plane-strain friction angle was chosen here because the mechanical analysis of retaining walls is a plane strain problem. The adoption of 2 kPa for soil cohesion instead of 0 was done to avoid numerical instability. Since the foundation soil was similar to the backfill, the same parameters were used for both materials for simplicity. The linear elastic constitutive model was selected to model the facing blocks and the leveling pad. The input parameter values for these concrete blocks (listed in Table 1) were determined by referring to [PERSON] et al. (2016) [12]. The reinforcements were modeled using the cable element of FLAC. Creep tests were conducted on the geogrids used in the SR-18 wall to obtain the reinforcement stiffness corresponding to the end time of construction (i.e., 4060 h). The test results showed that the creep stiffness at a 1% strain was 310 kN/m [10]. The selection of the stiffness value at a 1% strain was made so that the measured maximum strain in each instrumented reinforcement layer was close to 1%. The other parameters for reinforcements are attributed to the values recommended by [PERSON] et al. [41], as summarized in Table 2.  
All the concrete-concrete and concrete-soil interfaces in the wall were modeled using a linear spring-slider system, with the strength controlled by the interface friction angle and cohesion and the deformation controlled by the normal and shear stiffness at the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Backfill and Foundation** & **Blocks** \\ \hline Density \(\rho\) (kg/m\({}^{3}\)) & 2200 & 2400 \\ Cohesion \(c\) (kPa) & 2 & - \\ Plane strain friction angle \(\varphi\) (\({}^{\circ}\)) & 54 & - \\ Dilation angle \(\psi\) (\({}^{\circ}\)) & 14 & - \\ Elastic modulus \(E\) (MPa) & 80 & \(3.2\times 10^{4}\) \\ Poisson’s ratio \(\
u\) & 0.3 & 0.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameter values for backfill, foundation, and concrete blocks. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Axial stiffness \(J\) (kN/m) & 310 \\ Ultimate tensile strength \(T\) (kN/m) & 62.5 \\ Cross-section area \(A\) (m\({}^{2}\)/m) & \(2\times 10^{-3}\) \\ Soil-reinforcement interface cohesion \(c_{\text{sr}}\) (kN/m) & 2.5 \\ Soil-reinforcement interface friction angle \(\varphi_{\text{sr}}\) (\({}^{\circ}\)) & 43 \\ Soil-reinforcement interface shear stiffness \(K_{\text{sr}}\) (MN/m/m) & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameter values for reinforcements. interface. For these two types of interfaces, cohesion is usually close to 0 and the normal stiffness is generally taken as 1000 MPa/m when the interface is horizontal [12; 17; 18; 19; 41]. The interface shear stiffness value is important for predicting the behavior of an interface but is inconvenient to obtain, especially for concrete-concrete interfaces. Hence, large, direct shear tests were performed on the concrete-concrete interfaces with different degrees of roughness to establish an interface shear stiffness calculation model for this type of interface. Partial test details and results were reported by [PERSON] et al. [32]. The shear stiffness data for each concrete-concrete interface under different vertical loads are plotted in Figure 3a. It should be noted that the interface shear stiffness was normalized by wall height and atmospheric pressure. Figure 3a shows that there was a logarithmic functional relationship between the normalized interface shear stiffness and the tangent values of the interface friction angle under each vertical load.