LOTUNG DOWNHOLE ARRAY .2. EVALUATION OF SOIL NONLINEAR PROPERTIES

The characteristics of soil response during earthquake excitations, at a site in Lotung, Taiwan are identified using the Lotung large scale seismic test (LSST) data. A technique is developed to evaluate soil sh ear stress-strain histories directly from the free-field downhole acce lerations. These histories are used to estimate variation of soil shea r moduli and material damping characteristics with shear strain amplit ude, and to assess the effects of pore pressure buildup. Soil stiffnes s properties are found to compare satisfactorily with those obtained t hrough laboratory tests conducted by the University of California, Dav is; the National Taiwan University; and the University of Texas at Aus tin. Pore pressure buildup appears to be accompanied by a reduction in soil stiffness. The information obtained in this study demonstrates t hat downhole accelerometer and pore pressure arrays offer a direct eff ective means of evaluating seismic soil properties.