Existing pile foundations supporting high-speed railways - especially those embedded in soft clays - are undoubtedly affected by the nearby embankment construction or excavation activity. The distance between the surcharge load point and an existing bridge pile foundation (d) is an important factor affecting the internal forces and displacements of the foundation system. Three-dimensional finite element models were created to investigate the behavior of a bridge pile foundation supporting a high-speed railway in China under the surcharge load. The analysis results compare well with the field data. The study results indicate that the internal forces and horizontal displacements of piles decrease with the increase of d. When d is less than 4 times of soft clay depth (h), the horizontal displacements of pile groups decrease linearly and rapidly with the increase of d/h ratio. When d is larger than 4h, the horizontal displacements of pile foundations decrease at a lesser degree with the increase of d/h ratio. Suitable d value can be determined based on the maximum allowable displacement of the superstructure under the normal operating condition.