Bio-Cementation Field-Scale Trials: Addressing the Challenges of Treatment Uniformity & Verification, Biostimulation, & By Product Management

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Bio-mediated soil improvement, and in particular the use of microbially induced calcite precipitation (MICP) as a natural bio-mediated cementation process for sand improvement, has progressed rapidly. We propose to directly address the critical issues of treatment uniformity & verification, bio-stimulation, and by-product management through modest field-scale trials that are supported by experimental and numerical modeling techniques. Specifically, we proposed to perform two field-scale trials in a deep test chamber using natural liquefiable sand. The first trial relies on bio-augmentation (injection of bacteria) in order to provide a low-risk ground-truth set of data unencumbered by the unknown spatial distribution of native bacteria that we face with bio-stimulation. This first experiment builds directly on extensive laboratory research, has high likelihood of success and thus will enable focus on treatment uniformity and verification using in-situ and laboratory geotechnical tests. The second trial will use bio-stimulation (activation of native sessile bacteria) that introduces the additional degree of freedom (spatial distribution of bacteria) but is also the most desirable field scale treatment approach for the future. It is more practical (cost, permitting), has reduced by-product generation, and may increase uniformity. Both trials will enable study of by-product generation during treatment and its fate after soil improvement. We believe that field-scale treatment in a large test chamber provides the necessary balance between length scale and experimental control to rigorously, but practically, address these issues. The full-scale work will be supported by parallel efforts developing a robust bio-stimulation technique and modeling of the field trials to develop a predictive modeling tool that accounts for bio-stimulation, by-product transport and fate, and spatial heterogeneity. The scope builds on the team?s continued research activities over the past eight years, making this a challenging, yet feasible, scope. We envision that successful completion of this project will be transformative through improvement in treatment uniformity, validation of verification tests, development of a bio-stimulation approach, and management by-product generation and fate. Bio-mediated soil improvement is a relatively new, novel technique for improving the engineering properties of soils to a level where civil infrastructure can be supported. In particular, microbially induced calcite precipitation, or MICP, is a process in which microbial activity in the soil temporarily modifies local environmental conditions such that calcite crystals bind soil particles together. In the laboratory loose, liquefiable sand can be transformed into sandstone-like material in a matter of days. MICP is also attractive in that it uses less energy, and may be more sustainable than existing technologies using man-made chemicals. This research project is up-scaling the technology towards full-scale field deployment. Focus is placed on particular issues that directly influence the cost, environmental impact, sustainability, uniformity, and permanence. These issues include stimulation and utilization of naturally existing soil bacteria, optimization of treatment formulation, and optimization of the physical injection technique. This will be studied through a combination of numerical and experiment work across length scales from about 10 cm up to 5 m.