SEISMIC REFLECTION IN AN UNSATURATED SURFACE SOIL LAYER

摘要

Because of groundwater, soil is often modeled as a porous medium that is composed of a solid skeletonand water-filled pore spaces. In reality, however, it is a common situation that surface soils are notcompletely saturated. The partial saturation condition can be caused by fluctuation of water tablesassociated with natural or man-made processes. A detailed analysis of the 3-D borehole array records at areclaimed site subjected to the 1995 Kobe earthquake has indicated that the saturation condition of nearsurfacesoils may play a key role in the amplification of vertical ground motion. A great concern thusarises with further identification of the effect of saturation on seismic ground motions. In this paper, ananalysis is made of a soil layer overlying rock formations subjected to inclined (SV) waves from the base.Both the soil and the bedrock are modeled as a partially saturated porous medium that is characterized byits degree of saturation, porosity and permeability. Attention of the present analysis is focused on theeffect of saturation of the soil layer on the surface amplitudes and on the frequency-dependentamplification in both horizontal and vertical components. It is found that a change in degree of saturationhas a significant influence on the frequency-dependent amplification in the vertical component but anegligible effect on the horizontal component. Generally, a greater amplitude ratio between the twocomponents (denoted by V/H) may occur in a partially saturated soil layer.