## 5 Analysis of the Effect of Landslide Treatment
### Analysis of the Effect of Landslide Treatment  
Combined with the analysis of the causes of the landslide accident, it is necessary to address both settlement and stability issues. Additionally, improving the horizontal bearing capacity of the composite roadbed as a whole is crucial. The treatment for this road section focuses on enhancing the skidding resistance of the composite roadbed. The proposed treatment program includes unloading the roadbed, filling in the sliding section, and replenishing pipe piles. The pile diameter is adjusted from 0.3 to 0.4 m, and the pile length is increased to over 24 m. The pile body layout consists of square piles, while the row of hooded piles within the shoulder does not have tie beams. For the four-five rows of piles \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Form** & **Monopile Form** & **With Pile Caps** & **Transverse Tie** & **Longitudinal Tie** & **Longitudinal and Transverse Tie** \\  & & & **Beams** & **Beams** & **Beams** \\ \hline Maximum settlement (mm) & 621.74 & 313.68 & 177.63 & 179.61 & 174.92 \\ Safety factor & 1.117 & 1.321 & 1.882 & 1.831 & 1.993 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Maximum settlements and safety factors for stabilization of different structural forms. Figure 11: Finite element computational modeling and meshing of longitudinal and transverse tie beam forms. (**a**) Finite element calculation model; (**b**) meshing. outside the embankment shoulder, PHC piles with longitudinal and transversal tie beams were used. To prevent local slope sliding and ensure the overall stability of the composite roadbed, the overall structure of the composite roadbed incorporates longitudinal and transverse tie beams for four-five rows of piles outside the shoulder of the embankment. The treated composite roadbed is illustrated in Figure 12.  
Reinforcement was in the form of a PHC pipe pile composite roadbed monolithic structure with tie beams, i.e., below the shoulder of the embankment. The tops of the PHC piles were rigidly connected together by tie beams, and tie beams with a section width of 0.8 m and a section height of 0.7 m were arranged in the longitudinal and transverse directions of the tops of the piles to increase the longitudinal and transversal stiffness of the original PHC pipe pile composite roadbed and to realize the effect of vertical settlement control and horizontal slip resistance. As the existing reinforced bedding layer was damaged after the landslide, the bedding layer had to be reset. The reinforced bedding layer plays a very important role in coordinating the pile/soil load ratio of the PHC pipe pile composite roadbed, and also reduces the differential settlement between the pipe pile and the soil between the piles. Thus, the upper load of the soil between the piles can be transferred to the top of the pipe pile more effectively. In order to improve the overall strength of the bedding layer and reduce the construction damage, 0.5 m-thick gravel bedding was laid at the bottom of the composite roadbed, and one layer of finely knitted, bi-directionally stretchable geogrids made of GSJ 100 high-strength polyester filament, and one layer of reinforcing mesh of \(\varphi\)12 mm @ 20 cm \(\times\) 20 cm were set up to be sandwiched in the middle of the gravel bedding layer. The particle size of the graded gravel used was limited to a maximum of 30 mm. The settlement comparison curves of field monitoring and finite element modeling and the final settlement contours of finite element modeling over time are shown in Figure 13.  
The results indicate that the cumulative settlement of the composite roadbed is less than 200 mm, and the settlement remains stable with pile load pre-compression (\(<\)5 mm/month). The treatment and reinforcement measures have significantly improved the overall stability and bearing capacity. Furthermore, no landslide accidents occurred during the construction process, meeting the requirements for road use.