One of the key concerns of Geotechnical engineers has been how to improve soil behavior to mitigate geo-hazards. This research addresses the utilization of in-situ microbial biofilm formation on mineral surfaces as a means of soil improvement. Despite extensive research efforts on biofilms in a wide range of engineering applications, current knowledge of biofilm-mineral interactions in geologic materials is still in its infancy. The objectives of the proposed research are to quantify the interactions between biofilms and soil minerals, and to identify the effects of such biofilm-mineral interactions on the mechanical properties of soils. The primary emphasis is to explore the hypothesis that the biofilms produced by soil bacteria coat soil minerals and increase the mechanical strength and stiffness of soils, the extent of which will be dependent on physicochemical properties of the soil mineral, pH and ionic strength of pore water, as well as confining stress. This research will be among the first efforts to investigate biofilm associated soils from a geomechanical point of view, and will use various multi-scale experimentation techniques such as atomic force microscopy, X-ray computed microtomography, geophysical monitoring, and triaxial strength testing. The combination of those techniques will allow examination of the effects of mineralogy and pore water chemistry on adhesion forces of biofilms to minerals, biofilm growth patterns in pore spaces, and shear behavior of soils undergoing biofilm growth. Therefore, the specific aims of the proposed research are to select a model bacterium via characterization of the composition and structures of biofilms grown on mineral surfaces; to quantify the interactions between model bacterium biofilms and soil minerals at the nanoscale; to visualize the three-dimensional morphological patterns of biofilm growth in pore spaces of soils at the microscale; and to identify the effect of biofilm formation on geomechanical behavior of soils at the macroscale. Success of the proposed research will advance the understanding of the roles of biofilm formation in enhancing soil behavior, by identifying the most relevant factor related to mechanical behavior, investigating the extent of enhancement of soil strength and stiffness, and providing experimental data for development of a theoretical mechanistic model of biofilm-associated soils.
Society will benefit from the advancement in understanding of biofilm formation in geo-media and the development of the intelligent use of microbial biofilms to improve ex-situ and in-situ soil properties. The use of biofilms may improve hydrologic engineering barriers; controlled bio-remediation methods of contaminants, and sustainable soil improvement methods for mitigating of soil erosion, debris flows, and slope instability. Moreover, the outcome of the research will have broad impact related to engineering applications to natural and engineered porous media, such as biomass accumulation in near-surface soils of agricultural/farm lands, bio-clogging during natural oil and gas production, microbial enhanced oil recovery using selective plugging, biofilm development in microbial fuel cells, or biofuel processing. The cross disciplinary nature of this research gives graduate and undergraduate students unique experiences and opportunities that integrate bioscience, surface physical chemistry, and geophysics with geotechnical engineering. In addition, the proposed educational and outreach activities with high school teachers will broaden the participation of underrepresented groups and minority students in engineering, strengthen their scientific and engineering foundation, and stimulate their interest in engineering. The research and educational results will be broadly disseminated to the public and scientific community through publications at peer-reviewed journals and professional conferences, exhibition of demo hands-on modules with the high school teachers at regional conferences, and dissemination of the description of the demo hands-on modules through university websites.