Cut-off Wall for “Old” Dams for Restricting/Preventing Leakages/Seepages-Paper

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The paper reviews cut-off walls as a common way to reduce seepage, prevent water loss, and improve the stability of existing dams and other water-retaining structures.<br /><br />It describes two construction methods. Trench-cutter diaphragm walls are formed by excavating a supported trench, typically in a series of rectangular panels. In a one-phase process, self-hardening bentonite-cement slurry remains in the trench as the barrier. In a two-phase process, temporary support slurry is replaced with barrier material, such as plastic concrete. Cutter Soil Mixing (CSM) instead mixes the in-place soil with hardening slurry using horizontally rotating cutting wheels. Overlapping panels create a continuous wall, installed either fresh-in-fresh or by cutting into hardened adjacent panels. CSM can use one- or two-phase mixing procedures.<br /><br />Four projects illustrate the methods in challenging conditions. At Alaska’s Red Dog Mine, a trench-cutter wall was keyed into low-permeability bedrock beneath a tailings impoundment in warm permafrost. At the Dead Sea, trench cutters excavated difficult salt layers for a deep dike barrier. The Herbert Hoover Dike rehabilitation in Florida included about 90 km of cut-off walls, much of it built using CSM; organic soils were replaced and limestone pre-drilled to meet wall-quality requirements. At Rennersdorf, Germany, a CSM wall was installed to remediate a leaking flood-retention dam, with testing confirming reduced seepage.<br /><br />The paper emphasizes that method selection, ground conditions, suitable equipment and materials, and rigorous quality control are essential. Testing included production monitoring, wet samples, strength and permeability tests, and core inspections. The projects demonstrate that cut-off walls can successfully rehabilitate older dams and extend their useful service.

Keywords

cut-off walls

seepage control

dam rehabilitation

trench-cutter diaphragm wall

cutter soil mixing

plastic concrete

bentonite-cement slurry

permeability reduction

quality control testing

water-retaining structures