Slurry walls are impermeable barriers that can be used to prevent an unstable trench from collapsing or stop groundwater from entering a particular area. This technique involves digging a trench and filling it with a slurry of clay and water. In order to facilitate the construction of underground structures, the main purpose of a slurry wall is to keep unstable ground from collapsing before concrete can be poured. The same technique can be used to control the flow of groundwater in treatment systems and areas where subsurface contamination has occurred, though in those cases the slurry wall must be excavated to a particular depth and is typically never replaced with concrete.
The slurry wall technique has uses in both the construction and soil remediation fields. In both cases, the slurry is a semi-solid mixture typically made of clay and water. The thick suspension is solid enough to help maintain the integrity of a trench dug in soft ground, lighter than concrete and impermeable to groundwater. Each of these features is necessary for the construction of an effective slurry wall.
In construction projects, slurry walls can be used to facilitate the pouring of large, underground concrete structures. If the ground is solid, it is possible to simply dig a trench, lower in a form and then pour concrete to create a wall. When the ground is soft, saturated with water or otherwise unstable, an unsupported trench will tend to collapse in on itself. In order to support such a trench until concrete can be poured, slurry is pumped in as the excavation takes place. When concrete is later pumped into the bottom of the trench, it will naturally displace the lighter slurry.
The impermeable nature of clay and water mixtures can also be used in soil remediation projects and other activities that require the control of groundwater flow. In order for this type of slurry wall to be effective, the trench that contains it must be excavated deep enough to contact a naturally occurring layer of impermeable rock or clay. Water will then tend to flow around the slurry wall since the clay is already saturated, and will be unable to pass underneath due to the rock or clay below it. This can be used to redirect clean groundwater around a contaminated site or to completely contain an area. If a contaminated site is properly surrounded by slurry walls, the soil can then undergo remediation processes.