Collaborative Research: Implementation Strategies and Performance of Unsaturated Bio-Cemented Dune Sand

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This research will explore a novel approach for dune protection using bio-cementation to stabilize and enhance natural protective structures. Dunes often present the first line of defense for the built environment during extreme wave surge and storm events. In order to remain effective, dunes must resist erosion in the face of these incidents. Understanding the physics of dune erosion is critical for devising ways to mitigate it. The research team will explore multiple treatment implementation techniques and assess their performance under extreme conditions at field-scale in a large wave flume (LWF) at Oregon State University. Dunes will be constructed in the LWF, bio-cemented in-place, and subjected to a series of wave inundations so that their performance may be observed and quantified. The large-scale work will be supported by coupled laboratory and numerical investigations. The numerical investigation will provide insight into the loading conditions for which each treatment implementation alternative is preferred and the treatment design (e.g., required treatment dimensions) to have minimal impact on the natural environment while still providing the required engineering performance. The resulting outcome of this work will provide guidance for enhancing coastal dunes with bio-cementation to prevent damage to infrastructure during extreme events.Bio-cementation may be a viable method to mitigate dune erosion, which in turn would protect coastal infrastructure during extreme events. We will explore two approaches to implement bio-cementation. The first implementation technique will induce bio-cementation at depth within the dune; this will result in an uncemented surficial layer which may erode but will also minimally impact the coastal habitat. The second approach will be geared towards rapid deployment, for example, in preparation for a forecasted storm event anticipated to hit vulnerable dunes. This rapid approach will be sprayed onto the dunes, instead of injected, since this quick application is more likely to be implemented in a rapid deployment. Furthermore, two methods to induce bio-cementation will be explored: microbial induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP). The EICP implementation will be conducted by the NSF Engineering Research Center for Bio-mediated and Bio-inspired Geotechnics (CBBG). The research approach will include near prototype-scale experiments in the NHERI Hinsdale Wave Research Laboratory (HWRL); this is made possible by collaborating with an existing NSF project, Physics of Dune Erosion During Extreme Surge and Wave Events, which includes placing nearly 1000 tons of sand in the HWRL Large Wave Flume (LWF), the largest of its type in North America and in the top 10 in the world. In addition to the experiments in the LWF, a complementary laboratory testing and integrated numerical modeling program are planned to assess the effects of implementation strategies with overall dune performance. This research will advance bio-cementation technology by providing well-controlled and instrumented case studies to quantitatively compare the effect of implementation techniques on the performance of dunes. The resulting cementation patterns from the two treatment approaches are expected to be different; however, the performance of the two treatment approaches is unknown. This approach will not only develop prototype-scale case studies of two different treatment implementations, but also provide case studies of bio-cemented sand dunes subjected to extreme storm loading conditions. The numerical simulation approach will provide a framework to design and evaluate the stability of the bio-cementation under extreme wave loading.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.