# Study on the Seismic Effect of the Pebble Soil Site in the Zhongwei Basin
## 5 Conclusions  
This paper analyzes the seismic effect of pebble soil sites in the Zhongwei Basin. Based on the parametric analysis performed herein, the following conclusions can be drawn:  
1. Under different inputs, the variation in the pebble layer thickness has no obvious influence on the site surface peak acceleration, and the site PGA amplification ratio under different inputs is also significantly higher than the site PGA adjustment ratio, corresponding to the specification (GB 18306-2015). The influence of the pebble layer thickness on the ground surface acceleration response spectrum is primarily shown at 0.2\(\sim\)0.6 s at high frequency, and with the increase in the input field vibration, the difference is within the scope of the response spectrum curve. In this range, the pebble layer thickness of 30 m in the ground acceleration response spectrum spectral values is significantly smaller, and the response spectrum curves show the \"trough\" form; therefore, this kind of site has a certain \"weak isolation\" function in the middle/high-frequency band of 0.2\(\sim\)0.6 s.
2. Under the same pebble layer thickness, the ground surface peak acceleration increases with the upper silty clay layer thickness, and the PGA amplification ratio decreases with the increase in the input ground motion. Under the extremely rare earthquake condition, the PGA amplification ratio of the site is significantly lower than that of the other seismic effects, which fully reflects the influence characteristics of the site non-linearity on the ground motion. The pebble soil in the Zhongwei Basin has an obvious amplification effect on the short-period seismic waves, and the periodic peak points of the response spectrum are all within 0.1-0.2 s. Under extremely rare earthquakes, the response spectrum curve shows an obvious \"double peak phenomenon\", and the second peak point appears within 0.5-0.7 s periodic points. 3. With the increase in the input intensity, the PGA amplification ratio of the pebble-top interface is significantly smaller than that of the site surface. Under the extremely rare earthquake, the PGA amplification ratio of the pebble-top interface is less than one. Under the same earthquake action, the characteristic period of the pebble-top interface is significantly larger than that of the site surface. When the input intensity is  
Figure 13: The Fourier spectrum between pebble-top interface and ground surface under four seismic inputs. greater than the multiple earthquake action (50-63%), the characteristic period of the pebble-top interface is greater than GB 18306-2015. Under different intensity inputs, compared with the site surface, the calibration results of the pebble-top interface show the phenomenon of \"low amplitude and wide platform\", showing obvious shock absorption and isolation. Under different intensities of input, the acceleration response spectrum of the pebble-top interface shows a \"trough\" phenomenon at approximately 0.1 s, and the amplitude of the response spectrum is significantly lower than that of the bedrock input. Under the action of extremely rare ground motion, the acceleration response spectrum curve of the pebble-top interface shows a \"double peak phenomenon\", and within 0.24-0.4 s, the spectrum value is lower than the bedrock input. It can be concluded that the pebble-top interface has good damping and isolation effects. 4. Under the action of an earthquake, the energy of the pebble-top interface is concentrated in the low-frequency range of 1.1-2.2 Hz, and the amplification effect is obvious. In the range of 8-10 Hz, the amplitude is lower than that of the bedrock input, and the effect of reducing and isolating earthquakes is obvious. The site's surface presents the phenomenon of double superior frequencies, the energy is more concentrated in the high-frequency band, and the amplification effect is more significant. In future work, we believe that the following studies should be carried out for the seismic effects in the Zhongwei Basin.