CIVIL ENGINEERING

Na-bentonite has been used since at least the mid-1940s to create low-permeability in situ barriers to groundwater movement and to form in situ foundations for buildings in a practice known as slurry trench construction in this process, bentonite slurry is placed in a trench during excavation so that it is constantly kept filled.

As water from the slurry seeps out of the trench into the soil, the bentonite forms a thin film on the walls of the trench. This retards further water movement, allowing the hydrostatic pressure of the slurry against the bentonite film to stabilize the trench walls. With this practice, trenches can be excavated to depths of a hundred feet or more, even though highly unstable soils. Bentonite mixed with soil, cement, or other backfill materials, depending on the requirements of the project, may then be placed in the trench.

Such barriers have routinely been used to form stable, low-permeability cores during the construction of earth-filled dams. This technique is also widely used to form low-permeability barriers around hazardous waste sites to contain contaminants until site remediation is completed. Bentonite-based products are also used in boring tunnels for highways and subways, and for installing pipelines to transport drinking water, storm water, and sewage.

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