The present study attempted to explicate the scouring mechanism due to overflow focusing on the tractive force and the pore water pressure in the ground by using several geomaterials. For example; In the case of sandy soil, the scour profile has same profile as proposed by Yeh et al (2006), and the excess pore water pressure was generated. Especially, the excess pore water pressure was severely increased and it increased with the depth of sedimentation ground increased due to jet flow. As a result, the effective overburden pressure became zero, and a fluidization/liquefaction-like phenomenon occurred. Moreover, we investigated the mechanics of generate the excess pore water pressure in the ground induced by jet flow by using SPII method. As a simulation results, we found that the generating excess pore water pressure in the porous rigid ground was lower than the 1 g-field model test.