A simplified method for evaluating the liquefaction of sandy soil confined by a lattice-type deep mixing wall is proposed in this paper. The method calculates the cumulative excess pore water pressure from the initial shear strain using an equivalent shear-stiffness model created using a homogenization method. The proposed method uses parameters whose physical meaning is clearly defined, and can evaluate not only the effect of variations in the external forces but also the physical properties of the ground. This paper first explains the proposed idea and then presents the calculation procedure using an actual site plan.