**5. Conclusions**

In this study, the dynamic response analysis was performed on a shallow foundation used as a railroad pier through non-destructive tests. The full-scale model was conducted by constructing a full-scale model pier, and the effect of scouring was performed through the field pier test. Natural frequencies and phase differences were calculated by measuring the acceleration, and the modal number of piers was analyzed. The results of the study are summarized as follows.


**Author Contributions:** M.L. organized the paperwork, made a test plan, performed the impact load test; M.Y. and H.-S.J. helped the data analysis; K.H.K. performs numerical analysis; I.-W.L. supported making a test plan; all authors contributed to the writing of the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by a grant from R&D Program (PK2002A4) of the Korea Railroad Research Institute, Republic of Korea.

**Conflicts of Interest:** The authors declare no conflict of interest.
