Computation of individual contributions of two compression waves in vibration of water-saturated soils

Abstract

Water-saturated porous materials can sustain two types of compression waves, of which the second type is highly attenuated. Although the characteristics of independent waves of these two types are known, the knowledge of their individual contributions in dynamic response of saturated soils is limited. In this paper, a study is presented for a boundary value problem to quantitatively compute the individual contributions of these two waves. The problem corresponds to a water-saturated soil column subjected to steady-state vertical vibration at the base. The two-phase behaviour of soil is represented by the complete Biot's theory, which accounts for both viscous and mass couplings as well as the compressibility of constituents. A separation analysis procedure is presented which makes it possible to rigorously derive various responses such as displacement, total stress, pore pressure and relative fluid flow velocity in terms of the individual parts due respectively to the two compression waves. Numerical results are given to illustrate the behaviour of individual parts as affected by viscous coupling, mass coupling as well as loading frequency.