## 3 Results
### One-Third Frequency Range Analysis  
One-third frequency range analysis was used to explore the decay law of distinct frequency bands of vibration velocity with varying excitation and position changes. The energy distribution in various frequency ranges was also investigated [43]. The boundary frequencies of the 1/3 frequency range are calculated by the nominal value method, and the 1/3 frequency range diagram as shown in Figures 11-13 is obtained. Figure 10: Vibration velocity level decay frequency–domain curve. Figure 11: One-third frequency range analysis of the longitudinal decay curve. Figure 12: One-third frequency range analysis lateral decay curve. Figure 13: One-third frequency range analysis curve. Figure 11 demonstrates that each vibration frequency band decays with depth for a 100 km/h traveling test vehicle. The center frequency is divided into three bands with 5 Hz and 31.5 Hz as the boundary of the fundamental vibration frequency. The first band, 1-5 Hz, is mountainous with a noticeable peak, and as the depth increases, the peak shows a trend of decay. The frequency band is the test vehicle's principal influence band. In this band, attenuation of vibration in gravelly soil is more negligible than that of geocell-reinforced aeolian sand. At 2 Hz, the amplitude of vibration from the upper surface to the lower surface of gravelly soil increases. It results from the phase change caused by the heterogeneity of gravelly soil [44; 45]. The second band, 5-31.5 Hz, has apparent fluctuations on the pavement surface. In addition, the vertical attenuation is faster than in the first segment. This frequency band's vibration velocity accounted for a pretty considerable amount of the pavement's attenuation. Scheme 2's attenuation is more pronounced than scheme 1's. The geocell-reinforced aeolian sand layer on the pavement structure of the vibration diffusion effect is greater than the gravelly soil. The third section is greater than 31.5 Hz. This vibration section hardly varies with depth, indicating that the road excitation of a medium-sized bus is within 31.5 Hz. As frequency increases, longitudinal attenuation tends to accelerate. The faster the frequency of vibration, the greater the number of vibrations of the corresponding masses and the increased energy dissipated inside the soil [46; 47]. Figure 12 shows the one-third frequency curve for the 100 km/h test vehicle. The vibration of each frequency band of ground vibration decreases as horizontal distance increases. Additionally, the central frequency undergoes modifications. Under scenario 1, the primary frequency is 2.5 Hz, while the central frequencies at 2.9 m and 4.8 m are 2 Hz and 1.6 Hz, respectively, indicating that the central frequency of vibration tends to decrease with lateral diffusion. Scheme 2 attenuates the central frequency more than scheme 1 at greater horizontal distances. Under dynamic loading, the modulus of elasticity of gravelly soils falls. However, the polypropylene resin geocell maintains the stability of the structural layer with lower plastic deformation. Therefore, transferring the dynamic load to a larger horizontal range with smaller values [48; 49]. Figure 13a,c depicts a c as the one-third frequency line of the vibration velocity on the upper and lower sides of the gravel soil in scheme 1. Similarly, Figure 13b,d represents the one-third frequency line of the variation of the vibration velocity of the upper and lower sides of the geocell-reinforced aeolian sand for scheme 2. The central frequency of the test section of scheme 1 is 2.5 Hz, 2 Hz, 1.6 Hz, 2.5 Hz, 2.5 Hz, 2.5 Hz, and 2.5 Hz when the test vehicle passes at 20 km/h, 40 km/h, 60 km/h, 80 km/h, 100 km/h, 120 km/h. The main frequencies change from 2.5 Hz, 2 Hz, 1.6 Hz, 2 Hz, 2.5 Hz, 2.5 Hz, and 2.5 Hz on the upper side of gravelly soil to 2.5 Hz, 2 Hz, 2.6 Hz, 2 Hz, 2.5 Hz, 2.5 Hz on the lower side. The central frequencies of both Scheme 1 and Scheme 2 are a process of decreasing and then increasing with the increase in the driving speed of the test vehicle.