Site-Specific Earthquake Ground Motions for the 12th Street and 14th Street Viaducts on Route 139 in Jersey City, New Jersey

The 12th and 14th Street Viaducts, which carry Route 139, are located west of the Holland Tunnel in Jersey City, New Jersey. The two viaducts, supported on pile foundations, provide access to and from the Holland Tunnel (which connects New York City and New Jersey) and are considered critical structures. The New Jersey Department of Transportation (NJDOT) has selected DMJM+HARRIS to perform design services including rehabilitation and seismic retrofit for the 12th Street and 14th Street Viaducts. The subsurface conditions play a major role in evaluating the structures behavior under a seismic event. At the project site, the subsurface conditions consist of the following six strata: Loose to Medium Dense Sand (Fill), Peat/Organic Silt, Normally Consolidated Silty Clay, Silt/Sand, Weathered Rock and Bedrock. The magnitude of the seismic event will influence the response of these soil strata. The purpose of this paper is to present the results of a site-specific earthquake ground motions on rock. A probabilistic seismic hazard analysis (PSHA) was developed for this site. In addition, the paper will also present the results of site response analysis performed to compute ground motions at footing level and their associated response spectra. Values of soil amplification between the spectral acceleration of the footing level and the bedrock response spectra will be calculated and presented. A comparison of the resulting data to the current design spectra as defined in the 1998 New York City Department of Transportation (NYCDOT) Seismic Design Guidelines is presented. In order to determine the effects of the site soils on bedrock motions, it was required to define a soil profile with layer thickness and dynamic soil properties. The dynamic soil properties for the soil profiles were derived using a correlation with shear wave velocities obtained from cross hole surveys and from a correlation with standard penetration tests. Fourteen (14) soil profiles with two hazard levels having a return period of 500 years (probability of exceedence of 10% in 50 years) and a return period of 2500 years (probability of exceedance of 2% in 50 years) will be compared to the NYCDOT Class C, D and E soil profiles, which are appropriate for this site. The site response spectra were developed for the two level seismic events, using the computer program SHAKE. Nonlinear soil behavior is approximated by equivalent linear techniques implemented in SHAKE