## 1 Introduction  
A metro station was constructed using a combination of the traditional cut-and-cover method and the undercutting (hereafter, CCU) method [1, 2, 3], under the limitations of the project conditions. Many studies have been conducted on the seismic response of underground structures constructed using the cut-and-cover method, such as frame structures. These studies focus on the dynamic response patterns of structures under different seismic excitations [4, 5, 6, 7, 8, 9]. However, most studies simplify the frame structures as typical extensions of single-frame cross-sections along the longitudinal direction. As for the underground structures constructed using the undercutting method, such as culverts, many studies focus on dynamic response patterns. [PERSON] et al. [10, 11, 12] conducted numerical analysis on a soil-steel composite tunnel and a soil-steel composite bridge. Considering the seismic excitations input in different directions, the behavior of soil-steel composite underground structures is summarized. [PERSON] et al. [13] investigated the dynamic responses of a buried pipeline under longitudinal and transverse non-uniform excitations. The results indicated that the dynamic response mechanisms of the pipeline are relevant to the direction of seismic excitations. [PERSON] et al. [14] studied the seismic behavior of road box culverts using centrifuge model tests and a numerical analysis. The comparison between experimental and numerical results suggests that road box culverts have a good possibility of developing rocking rotation in the transverse excitation with great intensities. The structural configurations would differ from each other between the cut-and-cover portion and the undercutting part. Unexpected discrepancies in seismic responses were observed for the CCU structure under the longitudinal excitation of 1 g shaking tests [15]. Previous investigations presented that the direction of ground motion significantly influences the dynamic interaction of the junction between the shaft (constructed using the cut-and-cover method) and segmental tunnel (one of the undercutting methods). Therefore, it is crucial to pay closer attention to the effects of shaking direction on the responses of underground structures constructed using CCU methods. Model tests are an effective and widely used approach to study the seismic responses of underground structures. Several studies have focused on the seismic responses of CCU structures to transverse shaking. [PERSON] et al. [15] conducted shaking table tests on a shaft-tunnel junction, revealing that the tunnel section near the frame experiences greater axial force under transverse shaking. [PERSON] et al. [16] and [PERSON] et al. [17] investigated the soil-structure interaction and seismic responses of underground structures with two vertical shafts and a cut-and-cover tunnel. The earthquake motions in the shaking table tests were bidirectional (parallel and perpendicular to the axis of the tunnel, respectively). For metro station-tunnel junction structures, the interaction between tunnels and metro station frames exacerbates peak dynamic strains of the frame columns [18] and longitudinal strains of the tunnel [19], as indicated by shaking table test results with transverse input motions. [PERSON] et al. [20] conducted a series of shaking table tests to explore the effects of the shaft on the tunnel, revealing amplified accelerations, circumferential-joint extensions, and strains in the tunnel section near the shaft. [PERSON] et al. [21] identified the deformation modes of metro station-tunnel junctions under transverse input motions, highlighting the connection between the metro station and the tunnel as the weakest location due to stiffness mutation. [PERSON] et al. [22] conducted shaking table tests and a series of numerical analyses on a subway station-tunnel junction in liquefiable soil. The expansion joints between the station and the tunnel can reduce the seismic stress and deformations of the structure.