Deep Shear Wave Velocity Profiling in North Eastern Arkansas

Deep dynamic site characterization was conducted at fifteen ARDOT bridge sites in northeast Arkansas with the goal of developing shear wave velocity profiles to bedrock. A combination of active and passive surface wave methods along with horizontal to vertical spectral ratio measurements was used to develop the Vs profiles. These Vs profiles along with the methodology used to develop the Vs profiles are discussed. These Vs profiles were then utilized to develop an updated 3D velocity model (UA_MEVM) of the region for the purpose of conducting future site-specific ground motion response analysis (SSGMRA) for future ARDOT bridge projects. For one location in Monette, Arkansas, a full SSGMRA in accordance with the American Association of State Highway and Transportation Officials (AASHTO)guidelines was conducted using the Vs profile developed to bedrock. A combination of equivalent linear and non-linear site response analysis was utilized. Both analyses demonstrated attenuation of short-period seismic waves and amplification of long period waves. The attenuation in the short period range led to a reduction in the design acceleration response spectrum for the bridge of 1/3 for a period less than ~1.0 second. Using the updated design response spectrum from the SSGMRA, seismic aspects of the bridge were redesigned including retaining blocks, bent/columns, piles, and pile lengths, and approach embankment. A cost comparison between the original bridge designed using the AASHTO general seismic procedure and the updated bridge designed using the results from the SSGMRA indicated a potential gross cost-savings of $205,000 or approximately 7% of the original bid price was possible as a result of conducting the SSGMRA.