## 5 Summary and Conclusions  
In this study, a geogrid reinforcement was used, and a pullout test was conducted to propose a reasonable method for practical pullout parameters of reinforcements. The pullout tests were conducted to evaluate the effect of the tensile strength and the confining stress of the geogrid reinforcement on the pullout parameters. The pullout tests were analyzed using the effective confining stress method. Based on the pullout tests, the following conclusions can be drawn.  
1. With a reinforcement with the tensile strengths of 60 kN/m, 100 kN/m, and 150 kN/m, the reinforcement was fully pulled out and developed pullout characteristics. In this case, the pullout parameters were calculated using the relationship curves between the effective confining stress and the average pullout stress following the effective confining stress method, and were 26.17\({}^{\circ}\), 25.81\({}^{\circ}\) and 27.52\({}^{\circ}\), respectively, which are very similar and reasonable. Therefore, the effective confining stress method has been demonstrated to be a good evaluation method for finding pullout parameters, irrespective of the reinforcement tensile strength.
2. Based on the pullout test results, the pullout friction angle for the case considering all the confining stresses was much smaller than that for the case with the effective stresses that did not cause the rupture of the reinforcement. This is because the case, considering all the confining stresses, includes the confining stresses, caused the rupture of the reinforcement. Therefore, it was necessary to specify the low confining stress conditions to develop pullout force across the whole area of the reinforcement while conducting the pullout test for a geogrid reinforcement.
3. The pullout test result shows that the measured maximum pullout force depending on the tensile strength of the geogrid reinforcement was approximately one-third of the reinforcement tensile strength, and reinforcement rupture occurred while the pullout force greater than the maximum pullout force was exerted. Moreover, the pullout force was measured across the whole area of the reinforcement at the confining  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Confining Stress** & **Tensile Strength** & **60 kN/m** & **100 kN/m** & **150 kN/m** \\ \hline Total confining stress (kPa) & 13.99 & 13.94 & 22.53 \\ \hline Effective confining stress (kPa) & 26.17 & 25.81 & 27.52 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Pullout parameters depending on confining stress.  
stress smaller than one-half of the reinforcement tensile strength while pulling out the reinforcement.
4. In future, additional influencing factors such as the size and test procedure of the standardized pull-out test box and various pull-out test conditions are required to determine the pull-out constant that can be applied to the design of mechanically stabilized earth walls.  
Investigation, J.P. and H.N.; Supervision, D.K.; Writing--original draft, K.P.; Writing--review & editing, D.K. All authors have read and agreed to the published version of the manuscript.  
This study was supported from Chosun University, 2020.  
Not applicable.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
Data Availability Statement: Data will be available upon request.  
The authors declare no conflict of interest.