Lotung Downhole Array: Evaluation of Soil Nonlinear Properties

M. Zeghal*, Associate Member ASCE, A.-W. Elgamal*, Member ASCE,
H. T. Tang*, and J. C. Stepp*


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 shear stress-strain histories directly from the free-field downhole accelerations. These histories are used to: i) estimate variation of soil shear moduli and material damping characteristics with shear strain amplitude, and ii) assess the effects of pore pressure buildup. Soil stiffness properties are found to compare satisfactorily with those obtainedthrough laboratory tests conducted by the University of California at Davis, the National Taiwan University and the University of Texas at Austin. Pore pressure buildup appears to be accompanied by a reduction in soil stiffness.The information obtained in this study demonstrates that downhole accelerometerand pore pressure arrays offer a direct effective means of evaluating seismic soil properties.

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