## 4 Results and Discussion
### Full-Scale Model Results
#### 4.1.2 Tensile Forces in the Reinforcement Bars  
The tensile force \(F\) was calculated using Equation (4):  
\[F=\frac{\Delta I\cdot E\cdot A}{L} \tag{4}\]  
where \(\Delta I\) is the measured deformation on the reinforcement bars; \(E\) is the elastic modulus of the reinforcement material, where \(E\) = 210,000 Mpa for the CB300V steel; \(A\) is the cross-sectional area of the reinforcement bars, with \(A\) = 78.5 mm\({}^{2}\); and \(L\) is the length of the longitudinal reinforcement bars, with \(L\) = 2.1 m.  
The distribution of tensile forces in each reinforcement layer is shown in Figure 7. It can be seen that when the test load increased from 12 kN/m\({}^{2}\) to 302 kN/m\({}^{2}\), the tensile forces in the reinforcement bars increased and created a sliding surface within the reinforced soil.  
The maximum tensile force values were found 95 cm further away from the facing panel in reinforcement layers 3 and 4, and 60 cm (near the facing panel) in reinforcement layers 2 and 1 (the reinforcement layers in deeper positions).  
Figure 8 indicates that when the test load was lower than the design load (<20 kN/m\({}^{2}\)), the tensile forces in the deeper reinforcement layers were greater than the upper ones. However, when the test load was higher than 75 kN/m\({}^{2}\), the tensile forces in reinforcement layers 3 and 4 were higher than layers 1 and 2. It is a fact that at a low load level, the total load (including the earth pressure, dead loads, and surcharge load) increases with the depth of the wall. Thus, the deeper reinforcement layers absorbed a greater load than the upper layers. Conversely, when the load test was high, reinforcement layer 4 achieved the highest tensile forces and this value decreased along the wall depth. In addition, the increasing tensile force distribution when the surcharge load increased indicated that the failure surface expanded in the passive area.  
\begin{table}
\begin{tabular}{l c c} \hline
**Parameter** & **Unit** & **Value** \\ \hline _Backfill soil: concrete panel_ & & \\ Normal stiffness & Pa/m & \(2.4\times 10^{6}\) \\ Shear stiffness & Pa/m & \(2.4\times 10^{6}\) \\ Friction angle & Degrees & 26 \\ _Backfill soil: steel reinforcement_ & & \\ Shear stiffness & N/m\({}^{2}\) & \(2\times 10^{7}\) \\ Cohesion & N/m & \(1\times 10^{5}\) \\ _Initial apparent friction_ & & \\ _coefficient_ & & \\ Layer 4 & & 1.917 \\ Layer 3 & & 1.751 \\ Layer 2 & & 1.586 \\ Layer 1 & & 1.420 \\ \hline \end{tabular}
\end{table}
Table 4: Interface properties.  
Figure 7: The tensile force distribution in the reinforcement layers at different test load levels: (**a**) the fourth layer; (**b**) the third layer; (**c**) the second layer; (**d**) the first layer.  
Figure 8: Tensile force distribution in different reinforcement layers: (**a**) load level of 0 kN/m\({}^{2}\); (**b**) load level of 20 kN/m\({}^{2}\); (**c**) load level of 75 kN/m\({}^{2}\); (**d**) load level of 300 kN/m\({}^{2}\).  
The distribution of the tensile force in the reinforcement layers from this study was similar to the reports of [PERSON] (2013), [PERSON] et al. (2014), [PERSON] and [PERSON] (2017), [PERSON] et al. (2015), and [PERSON] and [PERSON] (2018) as well as design procedures ([PERSON] and [PERSON] (2018); [PERSON] and [PERSON] (2018); [PERSON] and [PERSON] (2018); [PERSON] and [PERSON] (2018)). However, the steel ribs included in the reinforcement grids caused a step in the tensile force distribution curve in front of and behind the ribs. This result was reasonable and similar to previous research results ([PERSON] and [PERSON], 2016; [PERSON] and [PERSON], 2016). It indicated that the experimental results from this full-scale model were reliable and could be used in practice.