Dispersive surface waves along partially saturated porous media

Numerical results for the velocity and attenuation of surface wave modes in fully permeable liquid/partially saturated porous solid plane interfaces are reported in a broadband of frequencies (100 Hz-1 MHz). A modified Biot theory of poromechanics is implemented which takes into account the interaction between the gas bubbles and both the liquid and the solid phases of the porous material through acoustic radiation and viscous and thermal dissipation. This model was previously verified by shock wave experiments. In the present paper this formulation is extended to account for grain compressibility. The dependence of the frequency-dependent velocities and attenuation coefficients of the surface modes on the gas saturation is studied. The results show a significant dependence of the velocities and attenuation of the pseudo-Stoneley wave and the pseudo-Rayleigh wave on the liquid saturation in the pores. Maximum values in the attenuation coefficient of the pseudo-Stoneley wave are obtained in the 10-20 kHz range of frequencies. The attenuation value and the characteristic frequency of this maximum depend on the liquid saturation. In the high-frequency limit, a transition is found between the pseudo-Stoneley wave and a true Stoneley mode. This transition occurs at a typical saturation below which the slow compressional wave propagates faster than the pseudo-Stoneley wave. (c) 2006 Acoustical Society of America.