NEESR-II: Biological Improvement of Sands for Liquefaction Prevention and Damage Mitigation

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This award is an outcome of the NSF 08-519 program solicitation ''George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)'' competition and includes the University of California at Davis (lead institution) and Lafayette University (subaward). The project will utilize the NEES equipment site at the University of California at Davis, which consists of a state-of-the-art geotechnical centrifuge (http://nees.ucdavis.edu). Our project vision is to evaluate and establish the potential of a bio-mediated ground improvement process to increase soil resistance to liquefaction triggering and to reduce the consequences if liquefaction does occur in the surrounding soil. The bio-mediated ground improvement process that will be implemented utilizes the biological activity of naturally occurring microbes to create the environmental conditions necessary for calcite crystals to form and bind soil particles together (www.sil.ucdavis.edu). This process is akin to the natural geologic process of sands and produces similar results, namely sandstone-like material. A bio-mediated approach is attractive since it is a naturally occurring process that is simply being accelerated.In this project we will examine how the treatment of liquefiable soils with the bio-mediated soil improvement method prevents/limits the occurrence of liquefaction and the performance of buildings supported on bio-improved soil. The UC Davis NEES centrifuge facility will be used to create scaled structures (buildings) supported on liquefiable soils. Zones of the soil directly beneath the building will be treated. The model will then be subjected to field (real) scale stress conditions by spinning the centrifuge. During spinning the models will be subjected to earthquake shaking and the performance of the soil and the structure will be measured with displacement, pore pressure, and accelerometer transducers in addition to high-speed video. This interdisciplinary research has the potential to transform the way in which earthquake-induced damage to civil infrastructure is mitigated. It also represents a significant contribution to the field of bio-soil engineering, a new emerging field at the cross-roads of civil engineering, microbiology, and geochemistry. In addition to providing direct insight into mitigating hazards associated with liquefiable soils, bio-mediated ground improvement processes have the potential in the future for dam and levee safety, tunneling, environmental barriers, groundwater protection, aquifer storage, energy storage, and geologic CO2 sequestration. The project will also be involved in the education and training of undergraduate and graduate students for this new interdisciplinary field. Data from this project will be made available through the NEES data repository (http://www.nees.org).