## 1 Introduction
This method has been employed in high-speed railway projects for numerous years, demonstrating its efficacy in effectively resolving the challenge of postconstruction differential settlement within soft-soil foundations subjected to traffic loads [18]. Furthermore, research has revealed that the uneven settlement within the transition section can be mitigated by incorporating a rigid-flexible gradual-transition section [19; 20]. Tailoring the pile-slab structure design theory to align with the distinctive attributes of highway roadbed structures and traffic loads, the adoption of the gradient pile-reinforced-concrete slab composite foundation unquestionably represents an innovative approach to tackle the pivotal challenges encountered in the aforementioned project. The dynamic response of the roadbed serves as a direct indicator of its dynamic stability under the influence of dynamic forces imposed by traffic loads and is contingent upon various influencing factors [21]. The acquisition of dynamic response characteristics constitutes the fundamental groundwork for assessing the functional attributes of the roadbed [22]. The settlement, being the most perceptible manifestation of the roadbed's behavior, offers invaluable insights into its operational performance. Highways' dynamic response and settlement behavior are typically analyzed through theoretical analysis, numerical simulations, and field-testing methodologies. Theoretical analysis is a valuable approach for deriving analytical principles. [PERSON] introduced a novel analytical solution for the dynamic response of transversely isotropic viscoelastic pavements employing the wave propagation method [23]. [PERSON] formulated an analytical layer element method specifically designed for the analysis of multilayer transversely isotropic saturated soils subjected to rectangular moving loads [24]. However, obtaining an exact solution for complex highway structural-layer materials can be challenging at times. As a result, numerical modeling was employed to surmount certain complexities inherent in theoretical analysis, providing an objective representation of the comprehensive attributes of the roadbed. [PERSON] advanced a finite-element model to emulate the behavior of embankment-structural transitions [25]. [PERSON] harnessed the finite-element method to contrast the dynamic response between two distinct transition zones located at the juncture of a bridge and a conventional roadbed [26]. It is imperative to underscore that both theoretical analysis and numerical simulations must be grounded in field testing, with their results necessitating comparison and validation to bestow engineering practicality [27]. This imperative arises from the fact that field-test investigations offer the most objective and realistic portrayal of the working state within the embankment [28]. Numerous studies have been undertaken concerning field tests conducted in railway-sector transition sections. [PERSON] scrutinized the attributes of peak dynamic displacements occurring along the track and transition subgrade under the influence of heavy-haul trains through field dynamic testing [29]. [PERSON] undertook field dynamic tests within the culvert-embankment-culvert transition zone, encompassing train operating speeds spanning 5-360 km/h, and revealed that the train axle weight and travel direction exerted a more pronounced influence on the sections and layers within the immediate vicinity [30]. [PERSON] executed field-monitoring tests within the context of the foam-concrete roadbed-culvert transition zone in a ballast railway and derived the relationship between the thickness of the foam-concrete layer and the dynamic response parameters [31]. Nevertheless, the existing body of literature on the dynamic characteristics of expressway transition sections remains relatively limited.