Cutoff walls are constructed by excavating narrow trenches under bentonite slurry and then backfilling (displacing) the slurry with higher density impermeable material (backfill) creating subsurface barriers that prevent the lateral flow of groundwater. These structures are used to contain the migration of contaminated groundwater, reduce the permeability of storage impoundments (such as tailings dams, ash ponds, or wastewater treatment ponds), and to prevent subgrade seepage in levee and dam construction. Design permeability and strength requirements, as well as native soil and groundwater conditions influence the composition of the engineered slurry backfill. Odin’s cutoff wall construction capability includes the ability to design and construct soil-bentonite, soil-attapulgite, soil-cement, soil-cement-bentonite, cement-bentonite and slag-cement-bentonite cutoff walls.
Typical cutoff wall designs include a hydraulic conductivity specification of less than 1×10-6 cm/sec, and an unconfined compressive strength between 30-300 psi. Odin can construct cutoff walls up to 93 feet deep using our specially-designed long reach excavator, and to depths over 93 feet using clamshell excavation or deep soil mixing (DSM) with nominal wall widths between 2 to 3 feet. Cutoff walls can also be designed to “key into” underlying confining layers (e.g. clay or bedrock) or can function as “hanging walls” (i.e. having a specified depth with no key).