Accurate numerical evaluation of uplift pressure is crucial for predicting building failure behavior during tsunami and flood disasters. The 2011 Great East Japan Earthquake Tsunami displayed cases where uplift pressure contributes significantly to building overturning and sliding failures. However, existing methods show poor agreement with experimental data and have difficulty in representing time-dependent pressure development underneath the structure. This study proposes a numerical method combining Moving Particle Semi-implicit(MPS) fluid analysis with Darcy-law based porous media theory to evaluate time-dependent uplift pressure and simulate building sliding and overturning in weakly coupled analysis. While porous media models have been applied to tsunami-induced pressure in foundations, coupled infiltration modeling that dynamically tracks wet-dry regions has rarely been reported. The method assumes a thin layer of porous media underneath the structure where water infiltration is governed by Darcy's law. The water distribution is represented by a dynamic wet-dry matrix which is used along with pressure boundary conditions to solve a Poisson equation for the uplift pressure underneath the structure. This pressure is integrated to obtain the uplift force and overturning moment acting on a polygon rigid body implemented in the MPS method. The MPS method simplifies the modeling of moving boundaries necessary to model structures involving large displacements which occur in the sliding and overturning of buildings. The effectiveness of the proposed method is compared with experimental data involving the sliding failure of structures exposed to dam break flows. The method accurately captures complex behaviors including delayed infiltration resulting in the gradual development of uplift forces and sliding-stop-resliding phenomena. An application to the Onagawa building collapse from the 2011 tsunami shows uplift pressure contributed approximately 52% of total overturning moment. These results demonstrate that the proposed method enables physically consistent evaluation of uplift pressure, providing a unified framework for predicting building failure modes under tsunami and flood conditions.