ON THE LINEAR SEISMIC RESPONSE OF SOILS WITH MODULUS VARYING AS A POWER OF DEPTH : THE MALIAKOS MARINE CLAY

The dynamic response of a soft and thick marine clay layer subjected to vertically propagating shear waves is obtained analytically. The deposit constitutes the topmost layer which will support a major 3.6 km long immersed tunnel in a high-seismicity region of central Greece. S-CPTU measurements show that the soil shear wave velocity varies with depth as Vs=mzp/2, i.e. with a zero value at the surface. It is shown analytically that the shear strain just beneath the ground surface of such a deposit either vanishes or tends to infinity, depending on the exact rate of increase of the shear wave velocity with depth, as reflected in the parameter p. The steady-state response is also studied and an analytical expression for the amplification ratio is provided, while the consequences of soil nonlinearity are highlighted.