ANALYSIS OF SITE LIQUEFACTION USING EARTHQUAKE RECORDS

The surface and downhole accelerations, and pore-water pressures recor ded during the 1987 earthquakes at a site in the Imperial Wildlife Man agement Area (Imperial County, Calif.) are used to obtain direct estim ates of the average seismic shear stress-strain and effective stress-p ath histories. These histories provide valuable insight into the site seismic behavior during liquefaction and associated loss of soil stiff ness. As the pore pressure increases due to seismic excitation, site s tiffness is found to gradually decrease. During the high-pore-pressure phase, site behavior is characterized by cycles of large shear strain and very small shear stress. At these large strains, evidence of hard ening response, possibly due to a dilative-type soil behavior, is obse rved. The results of this study demonstrate that acceleration and pore pressure histories recorded by downhole arrays represent a valuable d irect source of information on site response during seismic excitation .