During the construction of new bullet train line where excavating shallow overburden tunnel using NATM, a phenomenon of equal settlement of the ground surface, crown and foot of tunnel called an accompanied settlement occurred. Foot reinforcement side pile (FRSP) was used to prevent the ground subsidence and it had been reported that it could prevent settlement of ground and tunnel effectively. Nevertheless the mechanism of preventing settlement by using FRSP is still not yet clear. In this study, 2-D elasto-plastic FEM analysis is carried out to clarify the mechanism of the effect of FRSP. Phenomenon of accompanied settlement was simulated pertinently and the results indicate that FRSP can prevent ground subsidence by increasing effect of shear reinforcement, load redistribution and internal pressure.