## 3 Acceleration Response and Crest Settlement of Slope
### Horizontal Response Acceleration
The horizontal acceleration amplification factor distribution from the interior of the slope to its surface at a height of 15.8 m in the 2# model during centrifuge testing is as shown in Figure 7. The mean average acceleration amplification factors under each of the five levels of seismic load from the inside to the surface are 1.05 (A-4), 1.14 (A-179), and 1.29 (A-7), respectively, which shows the significant surface amplification effect. Figure 5: The amplitude ratios of the transfer function of the acceleration measured at A-3 (slope crest) and A-0 (bottom of the model box) in the 1#model during centrifuge testing. Figure 6: Maximum acceleration distributions along the normalized slope elevation in the 2# model in centrifuge tests: (**a**) deposit surface; (**b**) bedrock surface. Figure 8 shows the amplitude ratios of the transfer function of the acceleration measured at A-1(slope crest) and A-0 (bottom of the model box) in the 2#model during centrifuge testing. In addition to the frequency components at 5 to 7 Hz, the frequency components at 15 to 17 Hz are also significantly amplified as the seismic wave propagates from the bottom to the crest, and the amplification is even greater than that of components at 5 to 7 Hz. Comparison between unreinforced and reinforced slopes  
Comparing Figures 5 and 8, the spectrum amplification effect of the input seismic wave is changed significantly after the landslide is reinforced by stabilizing piles. This shows that the resonance frequency of the slope system is shifted from 5-7 Hz to 15-17 Hz after the stabilizing piles have been installed. To facilitate the analysis of the trend in the acceleration amplification effect inside the slope, the mean average value of the PGA amplification factors under multiple sequential ground motions was adopted at each measuring point, as shown in Figure 9.  
From Figure 9a, the mean average acceleration amplification factor in the upper part of the slope (A-179) is 1.326, which is greater than the magnification (A-4) at the same elevation within the slope (only slightly greater than 1); therefore, the different behaviors of the exterior and the interior of the slope will induce non-uniform movement. Qualitatively, the seismic waves transmitted from the bottom to the top create superimposed reflection and interference effects on the superficial layer, resulting in an acceleration amplification effect in the slope surface. Comparing Figure 9a with Figure 9b, it can be found that after the stabilizing piles are installed, the acceleration amplification factor near the slope surface is reduced compared with that beforehand. Stabilizing piles bridge the difference of acceleration response between the bedrock and deposit. The reason for the surface amplification effect can be explained as follows: part of the seismic energy is dissipated by damping during the propagation of seismic waves in the rock and soil mass, while the remaining energy is manifest as the seismic response of the rock and soil mass. The  
Figure 8: The amplitude ratios of the transfer function of the acceleration measured at A-1 (slope crest) and A-0 (bottom of the model box) in the 2# model during centrifuge testing. Figure 7: The horizontal acceleration amplification factor distribution from the inside of the slope to the surface of the slope at a height of 15.8 m in the 2# model in centrifuge tests. bedrock of the slope is harder than the upper part, so more energy is dissipated therein, and the dynamic response is smaller, while the surface soil mass of the slope is loose, and the dynamic response is greater [1,6]. The inconsistency in the acceleration (velocity or displacement) will lead to an inconsistency in the movement between the deposit layer and the bedrock layer. The uncoordinated movement between the shallow soil and the rock in the slope produces stripping tensile stress, and finally leads to the formation of a shallow surface landslide.