Hayward Bridge Geotechnical Array Soil Dynamic Properties

This paper infers shear wave velocity profiles and soil dynamic properties from acceleration recordings at the instrumented Hayward I-580/I-238 bridge site in California where two geotechnical downhole arrays are located. The geotechnical arrays include three-component accelerometers at the surface and various depths down to the depth of 90 m. A total of 15 earthquakes were recorded during 2011-2022 ranging from Mw3.4 to 6. The cross-correlation method was employed to determine the average shear wave velocity profiles. The estimated shear-wave velocity profiles show agreement with the results of corresponding P-S suspension logging data. In addition, the uncertainty envelopes for the shear wave velocity profiles were generated. Furthermore, the shear modulus and damping properties were calculated, which showed a more linear behavior at the east downhole array compared to the west downhole array, which was consistent with the sub-surface soil information. The damping ratios increased with shear strain and were generally less than 1.2%.