## 5 Numerical Results and Discussion  
Influence of Thickness of Lifted Layer on Mechanical Properties of CRTSIII Unballasted Track Structure  
Figure 10 shows the variation of stress at the bottom of track slab with different thickness of lifted layer. It can be seen that after grouting with cement-based mortar material and polymer material, the stress on the top of the track slab is similar along the cross section of the track slab, i.e., the tensile stress on both sides of the track slab is the largest, and the tensile stress is the lowest under the rail. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Part** & **Size/(m)** & **Elastic Modulus/(Pa)** & **Density/(kg/m\({}^{*}\))** & **Poisson’s Ratio** \\ \hline Rail & - & \(2.06\times 10^{11}\) & 7850 & 0.3 \\ Slab track & \(5.6\times 2.5\times 0.21\) & \(3.65\times 10^{10}\) & 2500 & 0.2 \\ Self-compacting concrete layers & \(5.6\times 2.5\times 0.1\) & \(3.25\times 10^{10}\) & 2500 & 0.2 \\ Base slab & \(16.84\times 3.1\times 0.28\) & \(2.7\times 10^{10}\) & 2500 & 0.2 \\ Surface layer of subgrade & & & & \\ (thickness) & 0.4 & \(1.8\times 10^{8}\) & 2000 & 0.25 \\ Bottom layer of subgrade & & & & \\ (thickness) & 2.3 & \(1.3\times 10^{8}\) & 1800 & 0.25 \\ Embankment filling (thickness) & 2 & \(8\times 10^{7}\) & 1700 & 0.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Structure parameters of unballasted track. Figure 9: Location of the void. (**a**) Overall perspective, (**b**) cross-sectional perspective, (**c**) oblique drawing of the section, (**d**) horizontal drawing of the section. Moreover, with the increase of lifting thickness, the tensile stress on the top of the track slab after lifting with cement mortar material decreases gradually, while the tensile stress on the top of the track slab after lifting with polymer material has no obvious change. Compared with the original complete pavement, the maximum tensile stress of the track slab after lifting with cement-based mortar material is significantly different from that of the original complete pavement, while the maximum tensile stress of the track slab after lifting with polymer material is similar to that of the original complete pavement. This is because the elastic modulus of pavement is similar to that of polymer and has good compatibility, while the elastic modulus of cement-based mortar and original pavement differs greatly. Figure 11 shows the variation of stress at the bottom of self-compacting layer with different thickness of lifted layer. It can be seen that when cement-based mortar is used to lift subsidence area, along the cross section of self-compacting concrete layer, the tensile stress on both sides is smaller and the tensile stress in the middle is larger, which differs greatly from the bottom tensile stress of original self-compacting concrete layer of complete pavement. With the increase of the lift thickness, the maximum tensile stress on the bottom of self-compacting concrete layer decreases gradually. However, the bottom tension stress of self-compacting layer restored by polymer has little change with the lift thickness, and it is similar to the bottom tension stress of self-compacting concrete layer of original complete pavement. Figure 10: Variation of stress at the bottom of track slab with different thickness of lifted layer. Figure 12 shows the variation of stress at the bottom of base with different thickness of lifted layer. In Figure 12, when cement-based mortar is used to lift the subsidence area, along the cross section of the base, the tension stress on both sides is smaller, and the middle tension stress is larger. The overall tension stress value is smaller than that of the original complete pavement base layer. With the increase of the lift thickness, the maximum tension stress on the bottom of the base layer decreases gradually. However, the bottom tension stress of the base layer restored by polymer has little change with the lifting thickness, and it is similar to the bottom tension stress of the original complete pavement base layer.