NSF East Asia and Pacific Summer Institute (EAPSI) for FY 2013 in New Zealand

Carter William L, Blacksburg VA

Investigators

Abstract

This action funds William Lake Carter of Virginia Tech to conduct a research project in Engineering during the summer of 2013 at the University of Canterbury in Christchurch, New Zealand. The project title is "Use of Surface Wave Tests for Evaluating the Efficacy of Ground Improvement Techniques for Mitigating the Risk from Earthquake Induced Liquefaction." The host scientist is Dr. Brendon Bradley. After the devastating 2010-2011 Canterbury earthquake sequence, the city of Christchurch, New Zealand is in a state of rebuilding. A particular focus is on mitigating future risk of damage from earthquake induced liquefaction at proposed building sites. Ground improvement technologies, like stone columns, reduce soil liquefaction potential by increasing the density and lateral effective confinement of the soil profile. However, the installation technique for stone columns is non-standardized and varies from company to company; stone columns installed by one technique may have a lower liquefaction potential than sites where stone columns were installed using another technique. This research determines the effectiveness of ground improvement techniques and their installation techniques by evaluating the improved sites using surface wave tests. Using Multichannel Analysis of Surface Waves (MASW) equipment, the PI performs active source, shear wave profiling of various improved ground sites around Christchurch and its environs. The tests are performed at the improved ground sites and adjacent unimproved ground sites to provide a comparison. Both sets of measurements are transformed into one-dimensional shear wave profiles and subsequently, compared to quantify the soil improvement defined by an increase in shear wave velocity across the site; an increase in shear wave velocity constitutes an increase in soil stiffness and resistance against soil liquefaction. Broader impacts of an EAPSI fellowship include providing the Fellow a first-hand research experience outside the U.S.; an introduction to the science, science policy, and scientific infrastructure of the respective location; and an orientation to the society, culture and language. These activities meet the NSF goal to educate for international collaborations early in the career of its scientists, engineers, and educators, thus ensuring a globally aware U.S. scientific workforce. Furthermore, the proposed research will continue to cultivate the professional and academic relationship between the University of Canterbury and Virginia Tech. It is also hoped that both research groups will learn from each other and further the profession's knowledge of earthquake risk mitigation worldwide. Stemming from this research will be an MS thesis, which will document the findings of this unique study. It is expected that the findings from this research will be shared with the earthquake engineering community by publishing the results in a high quality journal and/or a conference proceedings.