When deep cutoff trenches or higher strength backfill are required, plastic concrete cutoffs may be the optimum choice for the slurry wall backfill. Plastic concrete is a weak concrete with unconfined compressive strength typically in the range of 500 to 1500 psi, and a higher modulus of plasticity than regular concrete resulting from the addition of bentonite. Permeability can be as low as 10-9 cm per second. A small amount of bentonite slurry is used to increase the plasticity of the concrete.
Plastic concrete is often the material of choice for deep cutoff walls where consolidation of the adjacent soils is expected after the cutoff wall installation. Plastic concrete cutoff walls are usually constructed in alternating panels. Control of the verticality of the panels is critical to ensure continuity of the cutoff wall throughout its alignment.