NEESR-II: Study of Surface Wave Methods for Deep Shear Wave Velocity Profiling Applied to the Deep Sediments of the Mississippi Embayment

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ABSTRACTThe primary objective of this research project is to study testing methodologies for non-intrusively measuring shear wave velocity (VS) profiles of very deep sediments using low-frequency surface waves. Surface wave methods have become an accepted means to characterize soil deposits for site response studies and have compared well to established borehole methods. Several active-source surface wave methodologies, having varying degrees of sophistication and efficiency, currently exist. None of these methods, however, has been studied for application to the problem of very deep profiling (300 m and greater) of sediments. Most studies in the last 20 years have focused on the top 30 m with very few studies extending beyond a depth of 100 m. With the advent of the Network for Earthquake Engineering Simulation (NEES) large-scale field shakers, it is now possible to actively generate the low-frequency energy (down to 1.0 Hz) that is required for very deep soil profiling. Field studies will be conducted at several sites in the Central United States using a variety of data collection and data processing methodologies. The findings from this work will be applicable at other deep soil sites in seismically active regions around the country, including Salt Lake City, Utah, Los Angeles, California, and Charleston, South Carolina. The deep VS profiles derived from these studies will provide an additional benefit by filling a gap in the current state of knowledge of the stiffness structure of the deep soils of the Mississippi Embayment. Predicting the ground response in this seismically active region requires knowledge of the deep sediment structure, which extends to depths of 1000 m in some areas. Recent studies of the ground response in this region have been limited by a lack of knowledge of the deep soil stiffness structure. While the near-surface sediments (top 30 m) are generally well characterized, very few measurements have been performed to depths greater than 100 m. The VS profiles measured during these studies will be important input parameters for site response studies in this region. The findings from this work will be disseminated to the engineering community through peer-reviewed publications. Also, data sets will be placed on the NEES repository and will be a valuable resource for other researchers in this field. Educational field modules, demonstrating important concepts such as site resonance and soil liquefaction, will be developed by undergraduate students. These field educational modules will be included in demonstrations of this state-of-the-art field testing equipment to rural and minority K-12 students in the Central United States.