During the construction of the Bullet Train lines in Japan, several shallow tunnels were excavated in unconsolidated ground using the New Austrian Tunnelling Method (NATM). However, ground and tunnel settlements frequently occurred due to the low stiffness of the ground and the shallow overburdens. In order to prevent such settlements and to ensure the stabilization of the cutting face of the tunnels, a pr-ground improvement method was adopted in the above fields. Various combinations of improved areas and levels of strength were tried in the fields, and the tunnels were excavated successfully. However, the mechanism of the effect of the pre-ground improvement method, the influence of the strengh of the improved ground, and the influence of the depth and the width of the improved areas are not clearly understood. Therefore, 2D elasto-plastic FE analyses are carried out here to clarify the effect of the pre-ground improvement method on the prevention of ground and tunnel settlements.