A cutoff wall is a subsurface barrier constructed to restrict or prevent the movement of water, typically groundwater or seepage, through soil or rock beneath or adjacent to a hydraulic structure. In stormwater management and civil engineering, cutoff walls are used to control seepage, reduce underflow, and improve the stability and performance of structures such as dams, levees, detention basins, and embankments.
The primary function of a cutoff wall is to interrupt the natural flow path of water through permeable materials by introducing a low-permeability or impermeable vertical barrier. By doing so, it reduces the potential for water to pass beneath a structure, which can otherwise lead to problems such as piping, internal erosion, loss of stored water, or structural instability.
Cutoff walls are typically installed below grade and extend from the ground surface down to a less permeable layer, such as bedrock or a dense clay stratum. This creates a continuous barrier that limits seepage beneath or around the structure. In some applications, the wall is keyed into an impermeable layer to ensure effectiveness.
Several construction methods and materials are used for cutoff walls, depending on site conditions and design requirements. Common types include compacted clay cutoff trenches, soil-bentonite slurry walls, cement-bentonite walls, and steel sheet pile walls. Each type is selected based on factors such as soil permeability, depth requirements, constructability, and cost.
In stormwater applications, cutoff walls are often incorporated into the design of detention or retention basins to prevent excessive infiltration where groundwater protection or water retention is desired. They may also be used to control seepage around culverts, outfalls, or other hydraulic structures where uncontrolled subsurface flow could lead to erosion or failure.
From a geotechnical perspective, cutoff walls are critical for mitigating seepage-related risks, including uplift pressures, heaving, and internal erosion. Proper design requires an understanding of subsurface conditions, hydraulic gradients, and soil properties.
A cutoff wall is a key subsurface control measure used to manage groundwater movement and protect the integrity of stormwater and hydraulic infrastructure by limiting unwanted seepage paths.