Field Testing and Monitoring of an Experimental Soil-Bentonite Cutoff Wall

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Soil-bentonite slurry trench cutoff walls are widely used for seepage control, levee repair, and pollutant containment. Their widespread use in these critical applications requires a better understanding of their as-built condition and long-term behavior. Regarding the as-built condition, the in-place permeability of cutoff walls is heavily influenced by the presence of defects and by the stress within the wall. Conventional construction quality control programs are insufficient to verify backfill homogeneity throughout the installation, and commercial technologies are not yet available for non-destructively detecting defects or verifying the absence of defects. Regarding long-term behavior, several factors may cause changes in permeability of the wall over time including changes in stress and wet-dry cycling. This project seeks to address these questions regarding both the short-term (as-built) and long-term integrity of cutoff walls through the design, construction, in-situ testing, and monitoring of a fully instrumented cutoff wall to be installed near the Bucknell University campus. Society will benefit from better understanding and performance from our dams, levees and pollutant containment systems and from substantial teaching, training, and mentoring through the involvement of undergraduate and graduate students in the research, outreach to secondary students as part of the annual engineering summer camp, and exposure of students and practitioners to the state of the art/practice for cutoff walls via formal seminar presentations.The cutoff wall will be fully instrumented to monitor in-situ conditions in the backfill (e.g., 3D state of stress, vertical and lateral deformations, and pore water pressures) as a function of time and location. Electrical resistance imaging will be investigated for locating defects placed within the wall at known locations and of known size, with the goal of developing a viable geophysical methodology for defect detection in SB walls. The monitoring will be complemented with lab tests and in-situ tests (e.g., cone penetration, vane shear, dilatometer, and standard penetration tests), also performed over time to reveal time-dependent behavior. Finally, numerical model simulations to predict the stress distribution within an SB cutoff wall will be performed and the results compared with the measured field stresses. All field and lab data will be managed within a geospatial information system framework that will be made accessible to the public via the web.