Seismic Response Analysis of Offshore Seabed with Depth-Proportional Shear Modulus

Abstract

Referring to the results of the PS-logging performed at the boring site of the 150 m-deep seabed in Osaka Bay, it is found that there exists a relationship between the celerity of the transversal wave, vₛ (m/s), and the depth of soil layers, z (m) , as vₛ= 30z⁰.5. Other information obtained from the soil exploration also indicates that the seabed is almost normally consolidated at the site. These data show that the shear modulus increases proportionally with depth. In this paper, the characteristic function of such a ground is deduced by solving the fundamental differential equation, and the procedure of seismic response analysis is described. By the numerical calculation for a modeled seabed subjected to a simulated irregular seismic excitation at the base ground, it is known that, at the mudline, all responses reach their maximum values. In particular, the acceleration response attains as high as 4.7 times the input ground motion.