BIOLOGICALLY DRIVEN SOIL IMPROVEMENT

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Biologically Driven Soil ImprovementAward Abstract(Award # 0528171) Biological processes may provide great and previously unexplored opportunities for in situ, cost effective soil improvement. This research study will evaluate previously untested naturally occurring microbiological sequences that may be manipulated to dramatically improve the strength and stiffness of soil. The process aimed to replicate is the natural process that occurs when calcium carbonate precipitates in granular soil, resulting in a strongly cemented soil. Chemical precipitation of calcium occurs readily under aerobic conditions in a natural environment. In addition, it is known that aerobic bacteria can induce precipitation of the calcium present in the soil by drawing cations from the environment due to their negative surface charges. As a result of these processes, precipitation of calcium produces calcium carbonate precipitates. The precipitates arising from the process are highly insoluble and can be expected to increase the strength of the soil substantially by being adsorbed onto individual soil particles, leading to their strong cementation. The purpose of this exploratory research is to understand through a laboratory experimental program the conditions needed to recreate this natural process in situ with resulting advantageous effects on soil properties. To begin with, that would include investigating the impact of factors such as relative concentrations of calcite-oxidizing bacteria, the duration of each stage of the process, as well as the resulting improvement or degradation in soil strength, and possible changes in hydraulic conductivity. This process could ultimately be used either for site preparation before construction, for example, of either surface or underground construction, or for remediation of existing sites with soil conditions considered to be inadequate, including in earthquake susceptible soils. The broader impacts of the immediate study include improvement of earthquake susceptible soils and rapid construction during critical applications, such as military operations. The PI will hire undergraduate research assistants from underrepresented groups to work in the laboratory, aiming for diversity of academic background also. The PI has established a commitment to diversity among his research students and his experience has shown that undergraduates involved in research are more likely to continue onto graduate study.