Through the analytical solutions

the effects of saturated and unsaturated sediment on the dynamic pressures in the overlying ideal fluid due to P wave incidence from underlying elastic half-space are investigated. The sediment is modeled respectively as elastic solid

viscoelastic solid

ideal fluid and viscous fluid. The results obtained are compared with the case in which sediment was viewed as a two-phase poroelastic media. It is concluded that the two-phase poroelastic media can be simplified approximately as a viscoelastic or even as linear elastic solid when its permeability is relatively small (k≤10-3m/s). The findings are useful for construction a sediment model in dynamic analysis of dam-reservoir-sediment-foundation system to enhance the efficiency of the numerical procedures.