## 1 Introduction  
In the 21 st century world where science and technology are rapidly developing, the urban rail transit system represented by the subway has been vigorously developed, and gradually plays an increasingly important role in people's lives, not only facilitating people's lives, but also greatly promoting the economic growth [1; 2; 3]. However, with the denser subway lines and the increase in train speed, the environmental vibration problem caused by subway train operations has gradually become prominent. When the subway train runs along the subway line, the train wheel-rail contact is accompanied by the track irregularity, which produces an excitation effect and, in turn, produces vibrations between the vehicle and the track structure. The vibration will be transmitted to the ground through the basic structure, and may even cause secondary vibrations of adjacent buildings and noise, which have a greater impact on the work and life of residents along the line and the precision instruments of certain scientific research institutes. For some precious ancient buildings, the secondary vibration may also have an adverse effect on the safety of the structure [4]. Therefore, in the 20 years that the world has vigorously developed rail transit,the research on such issues has been extremely active. In most subway line segments, the ordinary monolithic track and the steel-spring-floating slab track are often laid alternately to ensure the vibration damping effect of the constructed line. Ordinary monolithic track structure often adopts cast-in-place sleeper-embedded track bed structure (Figure 1), which has good integrity and relatively low cost [5]. For the ordinary monolithic track structure system used in the primary vibration damping area of the subway track structure, the elasticity of the lower part of the rail is mainly provided by the corresponding fasteners. The rail fasteners can be used to adjust the overall mechanical and material properties of the track and adapt to the track geometry. Therefore, the design and manufacturing requirements are relatively high. The fasteners often need to have enough buckle pressure to ensure the safety of the train during operation, and also need to have a certain vibration damping effect, and facilitate maintenance and repair [6]. In this research, the vibration response of the ordinary monolithic track is used as a control group to compare the dynamic properties of the steel-spring-floating slab track. For special places with high vibration damping requirements, subway lines generally adopt a steel-spring-floating slab track structure, as shown in Figure 2. Its components include generally a concrete base, a steel-spring vibration isolator, a reinforced concrete floating slab, and fasteners. In this structure, elastic supports are added between the concrete bottom slab and the reinforced concrete floating slab [7; 8; 9; 10]. The elastic support has a certain adjustment flexibility. Both sides of the floating slab are fixed with elastic materials, and the rail is fixed on the floating slab with fasteners. At the same time, in order to ensure the coordination of the overall rigidity of the floating slab track, shear hinge devices are also provided at the ends of the two floating slab tracks [11; 12]. The steel-spring-floating slab track system is actually a mass-spring vibration isolation system [13]. The vibration isolation method is to float a reinforced concrete track bed with a certain mass and rigidity on the vibration isolation element, and uses the slab and the vibration isolation element to form a mass spring [14]. The vibration damping system adopts the mass inertia of the floating slab to balance part of the load of the train operation, and transfer the remaining load to the track bed, tunnel, and other structures to achieve the purpose of vibration damping [15].