An Experimental Study of Biopolymer Reduction of Cohesionless Soil Permeability for Landfill Cover Applications

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The overall objective of this CAREER initiative is to investigate the mechanisms governing the performance of alternative, evapotranspirative cover systems for waste containment applications while, at the same time, to develop alternative educational modules that will expose a wide range of populations (pre-, post-, and college students) to the challenges of environmental geotechnics. It is expected that this integrated research and education initiative will provide significant contributions through advancements in: (1) basic understanding of complex unsaturated flow processes, (2) combined centrifuge and numerical modeling, (3) design of waste cover systems in arid and semi-arid environments, (4) integration of research into engineering education, (5) teaching of design and of environmental geotechnics, and (6) outreaching strategies for minority high school students and the profession.Even though field monitoring programs and numerical simulations have provided invaluable insight into the behavior of earthen cover systems, the important task of validating predictive numerical tools remains, at best, incomplete. The research plan herein is then to use centrifuge modeling as an additional source of geotechnical data in order to gain further understanding into the complex unsaturated processes that take place in evapotranspirative covers. Centrifuge modeling will allow systematic control of the relevant variables, combination of weather and soil conditions critical for design, and significant reduction in the time needed for acquisition of experimental data. Of major relevance is the fact that, instead of generic soils, actual soils from two of the nation's most significant hazardous waste sites (California's OII Superfund Landfill and Colorado's Rocky Mountain Arsenal) will be used in the centrifuge models. These two sites are, respectively, currently implementing and seeking implementation of evapotranspirative cover systems. Rather than attempting to replicate actual prototype covers in the centrifuge, this research pursues validation and calibration of analytical tools used in cover analysis. Consequently, comprehensive unsaturated flow numerical simulations of the centrifuge experiments will be undertaken, followed by a careful parametric evaluation of generic prototype covers. This investigation will capitalize on the PI's past experience as centrifuge modeler and as designer and numerical modeler of the evapotranspirative cover at the OII Superfund site. Some of the major issues to be investigated through combined centrifuge and numerical modeling include the proper representation of surface flux boundary conditions, the sensitivity of the cover behavior to hysteresis in soil hydraulic properties, and the appropriate selection of the lower boundary condition in numerical simulations. Two educational modules, which are significantly related to and draw major strength from the research plan, will be developed as part of the education plan. The very same two modules will be used to achieve four specific engineering educational goals relevant to different populations. This effort will attempt to "bring the site to the campus" by developing: (i) a Multimedia Case History Series, and (ii) a Field Alternative Cover Demonstration. These educational modules will be used to address the needs for: (1) enhanced design experience for civil engineering undergraduate students, (2) curriculum development in environmental geotechnics for graduate students, (3) effective recruitment of underrepresented minority high school students into engineering programs, and (4) active outreach to the professional community, both locally and internationally. Through implementation of alternative, though still structured programs, the education plan will not only promote current advances in geoenvironmental engineering, but it will also address general deficiencies in engineering education.