Analysis of Site Liquefaction Using Earthquake Records

The surface and downhole accelerations, and pore‐water pressures recorded during the 1987 earthquakes at a site in the Imperial Wildlife Management Area (Imperial County, Calif.) are used to obtain direct estimates of the average seismic shear stress‐strain and effective stress‐path histories. These histories provide valuable insight into the site seismic behavior during liquefaction and associated loss of soil stiffness. As the pore pressure increases due to seismic excitation, site stiffness 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 hardening response, possibly due to a dilative‐type soil behavior, is observed. The results of this study demonstrate that acceleration and pore pressure histories recorded by downhole arrays represent a valuable direct source of information on site response during seismic excitation.