slurry wall

A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table. This technique is typically used to build diaphragm (water-blocking) walls surrounding tunnels and open cuts, and to lay foundations. Slurry walls are used at Superfund sites to contain the waste or contamination and reduce potential future migration of waste constituents, often with other waste treatment methods. Slurry walls are a "well-established" technology but the decision to use slurry walls for a certain project requires geophysical and other engineering studies to develop a plan appropriate for the needs of that specific location. Slurry walls may need to be used in conjunction with other methods to meet project objectives. Construction While a trench is being excavated to create a form for a wall, it is simultaneously filled with slurry (usually a mixture of bentonite and water). The dense but liquid slurry prevents the trench from collapsing by providing outward pressure, which balances the inward hydraulic forces and also retards water flow into the trench. The density of the slurry mix must be carefully monitored and adjusted to produce the correct outward pressure to prevent the trench walls from collapsing. Slurry walls are typically constructed by starting with a set of concrete guide walls, typically deep and thick. The guide walls are constructed near the ground surface to outline the desired slurry trench, and to guide the excavation machinery. Excavation is done using a special clamshell-shaped digger or a hydromill trench cutter, suspended from a crane. The excavator digs down to design depth (or bedrock) for the first wall segment. The excavator is then lifted and moved along the trench guide walls to continue the trench with successive cuts as needed. The trench is at all times kept filled with slurry to prevent its collapse, but the fluid filling allows the excavation machinery and excavation spoil to be moved without hindrance.