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1. Resisting Dune Erosion with Bio-cementation

   Montoya, B.M. ( October 2021 , 10th International Conference on Scour and Erosion)

   Coastal dunes often present the first line of defense for the built environment during extreme wave surge and storm events. In order to protect inland infrastructure, dunes must resist erosion in the face of these incidents. Microbial induced carbonate precipitation (MICP), or more commonly bio-cementation, can be used to increase the critical shear strength of sand and mitigate erosion. To evaluate the performance of bio-cemented dunes, prototypical dunes consisting of clean poorly graded sand collected from the Oregon coast were constructed within the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. The bio-cementation treatment was sprayed onto the surface of the unsaturated dune. The level of cementation was monitored using shear wave velocity measurements throughout the duration of the treatments. The treated and control dunes were subjected to 19 trials of approximately 300 waves each, with each trial increasing in water depth, wave height, and wave period. The performance of the dune was evaluated using lidar scans between each wave trial. The results indicate that the surface spraying treatment technique produced consistent levels of bio-cementation throughout the treated length of the dune and demonstrated significant resistance to erosion from the wave trails.
2. Resisting Dune Erosion with Bio-cementation

   Montoya, B. M. ( October 2021 , Proceedings of the 10th International Conference on Scour and Erosion)

   Coastal dunes often present the first line of defense for the built environment during extreme wave surge and storm events. In order to protect inland infrastructure, dunes must resist erosion in the face of these incidents. Microbial induced carbonate precipitation (MICP), or more commonly bio-cementation, can be used to increase the critical shear strength of sand and mitigate erosion. To evaluate the performance of bio-cemented dunes, prototypical dunes consisting of clean poorly graded sand collected from the Oregon coast were constructed within the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. The bio-cementation treatment was sprayed onto the surface of the unsaturated dune. The level of cementation was monitored using shear wave velocity measurements throughout the duration of the treatments. The treated and control dunes were subjected to 19 trials of approximately 300 waves each, with each trial increasing in water depth, wave height, and wave period. The performance of the dune was evaluated using lidar scans between each wave trial. The results indicate that the surface spraying treatment technique produced consistent levels of bio-cementation throughout the treated length of the dune and demonstrated significant resistance to erosion from the wave trails.
3. Bio-Cementation for Protection of Coastal Dunes: Physical Models and Element Tests

   https://doi.org/10.1061/9780784484050.042  

   Yazdani, E. ; Montoya, B. ; Wengrove, M. ; Evans, T. M. ( March 2022 , Geo-Congress 2022)

   Erosion of coastal dunes during storm events is an increasingly common problem in the face of global climate change and sea-level rise. To investigate the efficacy of bio-mediated ground improvement for reducing the impact of extreme events such as hurricanes, a near-prototype-scale experiment was performed. In the experiment, a model sand dune was constructed in a large wave flume and divided into treated and untreated zones which were instrumented with pressure and moisture sensors. One of the treated sections was subjected to a surface-spray technique to apply bio-cementation. Afterward, the dune was subjected to a discretized severe storm event (a scaled Hurricane Sandy) consisting of 25 trials. Surge runup and drawdown cause surface erosion and also internal instability due to liquefaction. Pore pressure sensors were embedded in different depths of the dune to study the pressure fluctuations during the wave action and the consequent momentary liquefaction phenomenon. Momentary liquefaction leads to detachment of fine sand particles and the initiation of internal erosion and sediment transport. In this project, remote assessment technology (lidar) was used between each trial to evaluate the performance of the dune under the surge flow by detecting the eroded volume of the sand. To better quantify materialmore »properties in-situ, a series of triaxial experiments were conducted on bio-cemented cores taken from the formed crust. The strength and stiffness of the cemented sand were measured under different drainage conditions. Element test results indicate a significant increase in critical bed shear stress (τc) due to cementation.« less
4. The Unique Ability of Fine Roots to Reduce Vegetated Coastal Dune Erosion During Wave Collision

   https://doi.org/10.3389/fbuil.2022.904837  

   Figlus, Jens ; Sigren, Jacob M. ; Feagin, Rusty A. ; Armitage, Anna R. ( July 2022 , Frontiers in Built Environment)

   Vegetated coastal sand dunes can be vital components of flood risk reduction schemes due to their ability to act as an erosive buffer during storm surge and wave attack. However, the effects of plant morphotypes on the wave-induced erosion process are hard to quantify, in part due to the complexity of the coupled hydrodynamic, morphodynamic, and biological processes involved. In this study the effects of four vegetation types on the dune erosion process under wave action was investigated in a wave flume experiment. Sand dune profiles containing real plant arrangements at different growth stages were exposed to irregular waves at water levels producing a collision regime to simulate storm impact. Stepwise multivariate statistical analysis was carried out to determine the relationship of above- and below-ground plant variables to the physical response. Plant variables included, among others, fine root biomass, coarse root biomass, above-ground surface area, stem rotational stiffness, and mycorrhizal colonization. Morphologic variables, among others, included eroded sediment volume, cross-shore area centroid shift, and scarp retreat rate. Results showed that vegetation was able to reduce erosion during a collision regime by up to 37%. Although this reduction was found to be related to both above- and belowground plant structures andmore »their effect on hydrodynamic processes, it was primarily accounted for by the presence of fine root biomass. Fine roots increased the shear strength of the sediment and thus lowered erosional volumes and scarp retreat rates. For each additional 100 mg/L of fine roots (dry) added to the sediment, the erosional volume was reduced by 6.6% and the scarp retreat rate was slowed by 4.6%. Coarse roots and plant-mediated mycorrhizal colonization did not significantly alter these outcomes, nor did the apparent enhancement of wave reflection caused by the fine roots. In summary, fine roots provided a unique ability to bind sediment leading to reduced dune erosion.« less
5. Experimental Study to Determine an EICP Application Method Feasible for Field Treatment for Soil Erosion Control

   https://doi.org/10.1061/9780784482834.023  

   Ossai, Rashidatu ; Rivera, Lucas ; Bandini, Paola ( February 2020 , Geo-Congress 2020: Biogeotechnics)

   The end goal of this research is assessing the feasibility of using enzyme induced carbonate precipitation (EICP) to create a cemented top layer to control runoff erosion in sloping sandy soil. The paper presents the results of an experimental study of bench-scale tests on EICP-treated sands to determine a treatment method feasible for field placement for this application. The soils tested were two natural sands and Ottawa 20-30 sand used as control. The EICP application methods were percolation by gravity, one-step mix-compact, and two-step mix-compact. Other conditions considered were pre-rinsing the sand prior to treatment, adjusting soil pH prior to treatment, and changing the EICP solution concentration. Promising results for this field application were obtained using the two-step mix-compact when the soil was first mixed with the urease enzyme solution before compaction. Considering that the EICP reaction starts once all components are added, this method would ensure that the reaction does not take place before the protective layer of treated soil has been installed. The effect of pre-rinsing the natural sand was not consistent throughout the testing conditions and its role in improving soil cementation in natural sand needs further study.