## 5 Conclusions  
Aiming at the shortages in exploring the transmission and evolution characteristics of the vibration signal, such as a few studies by using the jointed time-frequency domain and field prototypes tests, the typical subgrade compaction project of Jingxiong Intercity Railway Gu'an Station is selected to carry out the field prototypes tests, and the dynamic response from the vibratory roller to filling materials was monitored in the whole compaction process. Some efficient field tests data will be obtained. Based on this, the transmission and evolution characteristics of the vibration signal from the vibratory roller to filling materials in the compaction process are studied from time domain, frequency domain, jointed time-frequency domain and energy domain by using one new signal analysis technology, Hilbert-Huang Transform, which can relatively overall reveal the transmission and evolution mechanism of vibration wave. Some conclusions can be obtained as follows:  
First, during the propagation of the vibration signal from wheel to filling materials, the vibration acceleration peak gradually decreases with the increase of buried depth, and when the buried depth reaches 1.8m, the vibration acceleration peak is closed to zero. At the same time, when the vibration wave propagates from wheel to the surface of the filling, the attenuation rate of acceleration gradually increases with the increase of rolling compaction times, while the attenuation rate of other layers in different buried depth gradually decreases.  
Second, the vibration wave contains fundamental wave and multiple harmonics, and the dominant frequency of fundamental wave is nearly 21 Hz. With the increase of buried depth, the amplitude of fundamental, primary, secondary, until fifth harmonics decreases exponentially, and the concrete functional relationship among different amplitude of harmonics can be summarized as y = Ae\({}^{-\text{BX}}\). In the formula, A and B represent the coefficient, X represents the order of harmonic and Y represents the amplitude of harmonic when its order is X.  
Third, the vibration energy focuses on the fundamental wave and primary wave, which can increase with the increase of rolling compaction times, and when the rolling compaction time reaches five, their energy reaches maximum. However, when the filling reaches a dense situation, the energy  
Figure 13: Hilbert marginal spectrum of each measuring point of wheel and filling materials.  
of the primary wave gradually decreases. Therefore, the maximum rolling compaction time is five in the practical engineering applications.  
All authors contributed equally. [PERSON] is the responsible person for field tests, proposed the research ideas. [PERSON] is the site representative of field tests and help [PERSON] to finish the modification in the revised manuscript. [PERSON] finished the data process work and first version manuscript. [PERSON] provided the funding acquisition and help. [PERSON] helped [PERSON] to finish the field tests. All authors have read and agreed to the published version of the manuscript.  
This study is supported in part by National key research and development plan (No. 2018 YFE0207100); Natural Science Foundation of China (Contract No. 41731288); Sichuan provincial science and technology support project (No. 18 MZGC0186,18 MZGC0247, 2018Y0549); China national railway group co. LTD Scientific Research Project (No. SY2016G003, N2019G002; P2019T001); CHINA ACADEMY OF RAILWAY SCIENCES CORPORATION LIMITED Research and development fund (No. 2019 YJ026); 2017-2019 Young Elite Scientist Sponsorship Program by CAST. 2019 Young top talents Sponsorship Program of China Ten thousand people plan (No. 2019 YJ300); 2018 Sichuan province Ten thousand people plan; Nanchang Railway Bureau Scientific Research Project (No. 20171106), and CHINA RAILWAY ERYUAN ENGINEERING GROUP COLTD Scientific Research Project (No. KY2019145(19-20)).  
The authors declare no conflicts of interest.