Shear-wave velocity and attenuation analysis of liquefiable soils in the south Truckee Meadows, Washoe County, Nevada

Abstract

Within the sediment-filled basin of the south Truckee Meadows a soil liquefaction analysis demonstrated high potential for ground settlement and other deleterious effects due to strong ground motion associated with the design and maximum credible earthquake magnitudes assigned to this area. Detailed in-situ measurements of shear-wave velocity and bulk attenuation were obtained using state-of-the-art borehole geophysical techniques at three study sites. An important result was that liquefaction susceptibility (determined by standard engineering techniques) correlates with measured values of the anelastic attenuation factor and as more in-situ data become available this method should enhance correlation with standard engineering practice. The near-surface soils (^40 ft.) have shear-wave velocities ranging between 500 and 1500 fps, primarily dependent upon stiffness and relative density of the layer. Average Qs values computed from ratios of downhole signal Fourier spectra, for the frequency band 20 to 80 Hz, are 2.3-2.4 in (liquefiable) loose to firm silty sands, and 11.4-14.6 in (non-liquefiable) sandy gravels and silty clays.