## 4 Pullout Behavioral Properties Depending on Reinforcement Tensile Strength and Confining Stress  
Analysis of Relationship between Front-End Pullout Displacement and Pullout Force Depending on Reinforcement Strength  
Figures 5-7 show the relationship between front-end pullout displacement and pullout force obtained from the pullout test result for tensile strength (T\({}_{\text{g}}\)) of 60 kN/m, 100 kN/m and 150 kN/m of the geogrid reinforcement, respectively. With the reinforcement tensile strength of 60 kN/m, the confining stress was 0 (self-weight), 10, 20, 30, 40 and 60 kPa. With the reinforcement tensile strength of 100 kN/m and 150 kN/m, the confining stress was 0 (self-weight), 20, 40, 60, 80 and 100 kPa. In the figures, \(\bigstar\) denotes the maximum pullout force. Figure 4: Points on the geogrid for measuring displacement in the pullout box. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Test No.**} & \
\begin{tabular}{c} **Reinforcement Tensile** \\ **Strength (kN/m)** \\ \end{tabular} &
\begin{tabular}{c} **Confining Stress** \\ \(\sigma_{\
u}\) **(kPa)** \\ \end{tabular} \\ \hline
1–6 & 60 & 0 (self-weight), 10, 20, 30, 40, 60 (6 steps) \\ \hline
7–12 & 100 & 0 (self-weight), 20, 40, 60, 80, 100 (6 steps) \\ \hline
13–18 & 150 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Conditions of the pullout test. Figure 5: Front pullout displacement versus pullout force with confining stress (T\({}_{\rm g}\) = 60 kN/m). Figure 6: Front pullout displacement versus pullout force with confining stress (T\({}_{\rm g}\) = 100 kN/m). Figure 7: Front pullout displacement versus pullout force with confining stress (T\({}_{\rm g}\) = 150 kN/m). The reinforcement used in this study was a geogrid, which can experience reinforcement displacement, damage and rupture depending on the pullout force. After finishing the pullout test, the nodal displacement of the geogrid and the reinforcement were examined to observe reinforcement damages. No reinforcement damage was found after finishing the test. The pullout test showed that the pullout force increased as the front-end pullout displacement and the confining stress increased with the reinforcement tensile strength of 60 kN/m. Constant pullout force was shown while the reinforcement was pulled out with the confining stress of 0 (self-weight), 10 and 20 kPa. This implies that significant pullout resistance was exerted even with a small confining stress. Reinforcement rupture occurred with the confining stresses of 30, 40 and 60 kPa. Reinforcement rupture occurred with a relatively small reinforcement tensile strength and increasing confining stresses to result in great tensile force acting on the front side. The measured maximum pullout forces were constant, i.e., 20.3, 18.1, and 19.7 kN/m, respectively, with the confining stresses of 30, 40 and 60 kPa at which reinforcement rupture occurred. The pullout test for a reinforcement with tensile strength of 60 kN/m revealed that the maximum pullout force of 17.3 kN/m with the confining stress of 20 kPa (having enough pullout) was not much different from the maximum pullout force with rupture at higher confining stresses. With a small reinforcement tensile strength, the confining stress had great influence, and the confining stress-causing rupture was smaller. Meanwhile, with the reinforcement tensile strength of 100 kN/m and 150 kN/m, the pullout test revealed that the pullout force also increased as the front-end pullout displacement and the confining stress increased. With the confining stresses of 0 (self-weight), 20 and 40 kPa, it was shown that the pullout force remained constant while the reinforcement was pulled out. This implies that enough pullout resistance was exerted with smaller confining stresses. With the confining stresses of 60, 80 and 100 kPa, reinforcement rupture occurred. This implies that relatively smaller reinforcement strengths and increasing confining stresses produced great tensile force acting on the front side to cause rupture.