###### Abstract
Scholars have used finite element methods to analyze the dynamic characteristics of a high-speed railway subgrade system and obtained fruitful results [20; 21]. However, these studies are mainly based on the dynamic response in the continuous rock and soil medium, and they focus on the subgrade response characteristics. There are few reports on the response characteristics of soil in the ground of high-speed train crossing faults. Some scholars have carried out research on railway lines' crossing ground fracture sites. [PERSON] (2020) studied the Daxi (Datong-Xi'an) high-speed railway across the ground fracture in Taiyuan Basin, Shanxi Province by combining a field test, laboratory test, theoretical analysis and dynamic finite element numerical simulation. The research provided a scientific basis for the design of a high-speed railway foundation across the ground fracture zone [22]. [PERSON] (2019) analyzed the formation background, development status and distribution characteristics of ground fractures along the Neima railway. Combined with a large-scale indoor physical model test and numerical simulation, he studied the formation mode and propagation mechanism of ground fractures, but did not consider the related influence of ground fractures on the Neima railway [23]. [PERSON] et al. (2018) simulated the differential settlement of subgrade in the steep slope section of the Neima railway across the East African Rift Valley, but did not consider the influence of the upper load on the subgrade [24]. The landforms along the Beijing-Zhangjiakou high-speed railway are changeable. Among them, the Huailai section in Zhangjiakou is located on the compound of the Huaizhuo Basin and Yanfan Basin, and the Quaternary overburden is thick. In the basin, hidden active faults are developed, and the high-speed railway passes through the intersection of the Yanfan Basin northern margin fault and the Tumu-Huangtuyao fault. This key tectonic site is active today [25; 26]. The difference of soil engineering geological characteristics and the ground subsidence caused by a creep of hidden faults in the basin will undoubtedly affect the long-term safe operation of the Beijing-Zhangjiakou high-speed railway. The stratigraphic structure 500 m deep of a major project such as a high-speed railway has not been disclosed to the public. Previous studies on the deformation of high-speed railway foundations are limited to the long-term creep of static load or cyclic loading of dynamic load, and the deformation of a high-speed railway foundation across hidden active faults under different dynamic loads has not been considered. Considering the subgrade differential settlement of the Beijing-Zhangjiakou high-speed railway, this paper takesthe Beijing-Zhangjiakou high-speed railway (Huailai section) as the research object and reveals the deep soil stratum structure of the key tectonic site through deep-hole drilling. Based on the representative soil geotechnical tests, this paper studies the law of the physical and mechanical parameters of the drilled core soil in the key tectonic site changing with depth, and reveals the compression characteristics of the high-speed railway foundation under a static load. Furthermore, we constructed a three-dimensional geological structure model of soil based on faults, and take a reasonable train load model to simulate the impact of a high-speed train dynamic load considering the fault effects on land subsidence at different speeds. This will provide data support for the safe operation and deformation monitoring of the Beijing-Zhangjiakou high-speed railway, and also provide basic scientific and technological support for the planning and construction of similar major projects across the tectonic plates. The Engineering Geological Background of the Beijing-Zhangjiakou High-Speed Railway (Huailai Section)