# Comparative Test on the Bond Damage of Steel and GFRP Bars Reinforcing Soft Rock Slopes
## 3 Results
### Displacement of Anchorage Section under Loading  
During the loading, the top displacements of the steel and the GFRP bars under the condition of soft rock and expansive soil layer were recorded. The displacement of  
Figure 10: Strain-time curve of each point of the bar body under constant load 150 kN. (**a**) Anchorage depth at 0.75 m away from the zero point. (**b**) Anchorage depth at 1.25 m away from the zero point. (**c**) Anchorage depth at 1.75 m away from the zero point. anchorage section and other indexes are calculated, as shown in Table 6. Figure 11 shows the bars displacement of anchorage section under loading, showing a linear relationship. Figure 12 shows the gradients of displacement of anchorage section of two kinds of bars at different layers to compare the difference between the indexes of steel bar and GFRP bar in the anchorage section. The relative difference is equal to the ratio of the difference of displacement gradient of GFRP bar and steel bar to the displacement gradient of GFRP bar, and the calculating results are shown in Table 7. The gradient of the steel bar displacement curve is much smaller than the GFRP bar under the condition of soft rock, while the gradients are similar \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Geological** & **Specimen** & **Load/kN** & **Length of** & **Total Displacement** & **Free Section** & **Displacement** & **Displacement** & **Effective** & **Anchorage** & **Average** \\
**Conditions** & **Type** & **Log/m** & **Free Section** & **placement** & **Displacement** & **Section** & **Depth** & **Depth** & **Stress/MPa** \\ \hline \multirow{2}{*}{Soft rock} & Steel & 104 & 0.6 & 3.82 & 0.65 & 3.17 & 4.35 & 149 \\  & GFRP & 105 & 0.3 & 1.95 & 1.10 & 0.85 & 2.75 & 17 \\ \hline \multirow{2}{*}{Expansive soil} & Steel & 118 & 0.6 & 14.19 & 0.73 & 13.46 & 4.35 & / \\  & GFRP & 120 & 0.3 & 13.60 & 1.26 & 12.34 & 4.35 & / \\ \hline \hline \end{tabular}
\end{table} 
Table 6: State characteristics of anchorage section under loading. Figure 11: Bars displacement of anchorage section under loading. Figure 12: Gradients of displacement curve of anchorage section. under the condition of expansive soil. According to Figure 11, the small gradient means large displacement under the same load condition. Under the condition of soft rock, the relative displacement of anchorage section of the steel bar was much larger than the GFRP bar. This is because when subjected to the same load conditions, there is a large difference in elastic modulus between the steel bar and the grouting body. Thus, the deformation coordination between the bar body and the grouting body was poor, and the interface damage was serious. The force to balance the external force was mostly concentrated in the bar body itself and the bar body interface. The average stress in the anchorage section of the bar body was 149 MPa, as shown in the Table 6, which means that much more of the bar body participated in the deformation when subjected to tension. The elastic modulus of the grouting body is close to the GFRP bar, leading to a well-developed coordination between the bar and the grouting body. The force to balance the external force was mostly concentrated on the grouting body and the bar itself. The grouting body and the bar jointly resisted the external force. At this time, the average stress in the anchorage section of the bar was only 17 MPa, which means that only a small range of the bar body participated in the deformation. Therefore, the rate of deformation of the anchorage section of GFRP bar was much lower than the steel bar. This also shows similar behaviour under the condition of expansive soil; however, the displacement gradients of steel bar and GFRP bar are similar.