## 2 Overview of Engineering Background
The original plan, however, did not sufficiently restrain the lateral soil movement and settlement of the embankment, as indicated by the in situ observations of the deformations of the embankment and the pile head. Hence, two modified plans were considered to further reinforce the embankments: (i) widen the vertical piles and (ii) change the pile installation angle to form battered piles. The first plan is a simple method and can satisfy the engineering demand; most of the lateral displacements of the pile after reinforcement are within 30 mm, and the pile head settlement is about 20 mm. This plan is traditional but may not be economically efficient just for safety considerations. The latter plan seems more promising to address this problem, only by changing the installation angle to realize the reuse of originally designed piles. However, the reinforcement effect of battered piles on resisting the lateral soil movement has not yet been clarified. The behaviors of battered piles in terms of the optimum pile inclination would undoubtedly be the concern of this investigation, which entails a related scaled model test before the full-scale in situ test. Considering that the depth of the pile tip located at the foot of the embankment is much deeper than the critical depth of the possible failure surface, the geometry of the slope failure surface only provides some reference as the background information but is no longer the focus of the subsequent investigation. Focusing on the pile behaviors, the embankment was directly represented by a loading near the pile applied by the lever loading system. \begin{table}
\begin{tabular}{l c c c c} \hline
**Layer** & **Unit Weight \(\gamma\) (kN/m3)** & **Cohesion \(c\) (kPa)** & **Internal Friction Angle \(\varphi\) (\({}^{\circ}\))** & **Poisson’s Ratio \(\
u\)** \\ \hline Plain fill & 18.5 & 16 & 6 & 0.28 \\ Clay (soft plastic) & 17.2 & 10 & 3.6 & 0.35 \\ Clay (plastic) & 18.0 & 20 & 6.2 & 0.25 \\ \hline \end{tabular}
\end{table} 
Table 1: Main physicochemical properties of soil layers at K13 + 380. In addition, the type of soil was a secondary factor in the optimization of a feasibility investigation, especially when the pile was installed in strata with similar properties. Sand  
Figure 4: Piles resisting the embankment-induced lateral soil movement: (**a**) pile segment above ground; (**b**) pile-retaining wall connection. Figure 3: Embankment failure at K13 + 380: (**a**) failed embankment cross-section; (**b**) exposed sliding surfaces. is used in the model test because its physical and mechanical parameters are easier to control, and it is favorable for duplicating the test. Conceivably, if the optimum inclination with a proper constraint can produce the best pile performances when the clay is changed to sand, it will probably also work for the clay. That is, the conclusion obtained by using sand would be little affected by stratification, or the tendency would be similar because of strata with similar properties. This research aims to examine the performance of battered piles resisting the embankment-induced lateral soil movement by a series of reduced-scale model experiments of battered piles near the surcharges with a similarity ratio of 1:30. The effects of pile inclinations, surcharge magnitudes, and constraint conditions at the pile tip on the pile responses were considered in these experiments. The parameters for model design are listed in Table 2. The ratios of the geometrical parameters are supposed to be 1:30. However, not all of them can be exactly equal to 1:30 (such as the pile spacing) because of some restrictions, e.g., the size of the test tank. Consequently, ratios of some parameters can only be designed close to the targeted similarity ratio, and their differences would not heavily impact the results. The similarity ratios of the length of the segment above ground and pile embankment distance vary from 1:25 to 1:50 because this study has many problematic embankment sections.