Deep Shear Wave Velocity Profiling in North Eastern Arkansas

North-Eastern Arkansas is located in the heart of the New Madrid Seismic Zone, which is subjected to significant seismic hazards. NE Arkansas is also located inside the Mississippi Embayment, a geologic unit characterized by very deep soft sediment deposits. These two characteristics significantly increase the seismic design costs of bridges, abutments and deep foundations in NE Arkansas. Currently Arkansas State Highway and Transportation Department (AHTD) uses the generic design method in American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) manual to estimate the seismic demand for these structures. However, the manual clearly warns that short-period structures may be over-designed at a significant cost, and long-period structures may be under-designed at a significant risk. Therefore, the manual recommends the use of site-specific ground motion response analyses (SSGMRA) in evaluating the seismic demand to support structures on deep soil deposits. Recent studies (MBTC 3032 & AHTD Job BB0610, PI: Brady Cox) have demonstrated the potential cost saving of doing a more in-depth SSGMRA, which could allow the seismic design demand to be lowered by 33% permitted by the design manual. The initial phase for performing SSGMRA calls for collecting site information including shear wave velocity (Vs) profiles as main input to the analyses. Numerous investigators have attempted to measure shear wave velocity profiles in the Mississippi Embayment. However, most techniques for measuring Vs are not effective in covering the full depth of the soil sediments. The current research project TRC1603 focuses on developing deep shear wave velocity profiles to bedrock in NE Arkansas, which are one of the three main inputs into SSGMRA. These profiles are one step in reducing the high cost of highway structures, while maintaining their safety for travelers.