## 6 Conclusions  
A dynamic numerical analysis was conducted to investigate the stability of an inclined earth retaining wall used during an embankment construction. The main conclusions are summarized as follows:  
1. A dual support is more effective for suppressing lateral and vertical displacements than a single support. The resistance to the dynamic loading of a single support was shown to be smaller than that of a dual support.  
2. The most significant factor influencing a lateral displacement at the top of a retaining wall is the support type. The next most influential factor is the number of H-beams, whereas the least influential factor for the same number of H-beams is their arrangement.  
3. As with a lateral displacement, the most significant influencing factor on a vertical displacement at the top of the retaining wall is the support type. For a dual support, the next most influential factor was the H-beam arrangement, unlike a lateral displacement, and the least influential factor was the number of H-beams.  
4. The type of support is an important factor affecting both the lateral and vertical displacements at the front of the retaining wall. Other factors, such as the number of H-beams and the arrangement of the H-beam of the support, did not have much of an effect. The support type affected the direction of the lateral displacement behavior at the bottom of the retaining wall.  
5. The lateral displacement of the IER structure was shown to decrease by 81.05% at maximum compared to a one-row retaining wall with the same H-pile number per 10 m. An IER structure is therefore considered to be more stable.  
6. The lateral displacement decreased by 89.24% when the structure was installed under the same conditions with or without a back support. It is thought that the back support applied to an IER structure demonstrates a suppression pile effect. The installation of the back support was shown to increase the structural stability.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Lateral Maximum Displacement of Top** &
\begin{tabular}{c} **Lateral Displacement Ratio** \\ **(Standard/Type D)** \\ \end{tabular} \\ \hline A & 28.1 & 0.1076 \\ D & 261.2 & 1.0000 \\ F & 41.3 & 0.1581 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Lateral displacement ratio according to installation of back support.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Lateral Maximum Displacement of Top** &
\begin{tabular}{c} **Lateral Displacement Ratio** \\ **Standard/Type C** \\ \end{tabular} \\ \hline
**A** & 28.1 & 0.5063 & 0.6804 \\ C & 55.5 & 1.0000 & 1.3438 \\ E & 39.9 & 0.7189 & 0.9661 \\ F & 41.3 & 0.7441 & 1.0000 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Lateral displacement ratio according to installation interval of back support.  
7. For the same IER structure, the lateral displacement decreased by approximately 30% when the installation spacing of the back support was reduced by twofold.  
8. By using the operating load of the railway, the dynamic numerical analysis was conducted. The results show the substantial displacement suppression effect by using the IER method. Using IER method may significantly affect the stability of the embankment construction so that the use of auxiliary method such as anchor installation may be eliminated. In addition, the construction period can be shortened and economic efficiency is expected to be increased. Therefore, it is recommended to use the IER method in the future construction of embankments.  
Conceptualization and methodology, J.-C.I. and M.S.; software, S.-W.S. and J.-W.Y.; validation, S.-W.S. and M.S.; analysis, S.-W.S.; investigation, M.S.; writing--original draft preparation, M.S. and S.-W.S.; writing--review and editing, S.-W.S. and M.S.; visualization, S.-W.S.; supervision, M.S.  
This work was supported by a 2-Year Research Grant of Pusan National University and the National Research Foundation of Korea (NRF-2018R1A6A3A01011077).  
The authors declare no conflict of interest.