Experimental validation and applications of a modified gap stiffness model for granular marine sediments.

The author has proposed a modified gap stiffness model, which is incorporated into the Biot model; the resultant model is called the BIMGS model. By using this model, it is theoretically demonstrated that the frame bulk modulus is dependent on frequency [M. Kimura, "Frame bulk modulus of porous granular marine sediments," J. Acoust. Soc. Am. 120, 699-710 (2006)]. In this study, the modified gap stiffness model is reinvestigated and approximated expressions are derived for low- and high-frequency ranges. In particular, experimental validation of the BIMGS model is carried out. First, for glass beads and beach sands, the modified gap stiffness at a high frequency is experimentally obtained as a function of the grain size. Second, by using the measured values of the longitudinal wave velocities in the glass beads with two types of alcohol-water-mixed liquids, it is validated that the frame bulk modulus is a linear function of the fluid bulk modulus and that the frame bulk modulus is dependent on frequency, which can be derived from the BIMGS model. Finally, for applying the BIMGS model, it is shown that the reported velocity dispersion and the frequency dependence of attenuation, which cannot be explained by using the Biot-Stoll model with a constant frame bulk modulus, can be explained.