Cut-off walls are used to exclude groundwater from an excavation, to minimise the requirement for dewatering pumping. Typically, the process involves installing an extremely low permeability physical cutoff barrier or wall around the perimeter of the excavation to prevent groundwater from entering the working area.
Several approaches are accessible to form cutoff barriers or walls around excavations, including:
- Steel sheet-piling
- Slurry trench walls
- Concrete diaphragm walls
- Weary pile walls
- Grout impediments
- Combination-in-place barriers
- Man-Made earth freezing
The selection of a given exclusion process used to form a cutoff obstacle will be contingent on the conditions and constraints on a given project. Main restraints are desired depth of wall, ground conditions, geometry of wall (some systems can be used horizontally or inclined to the vertical, while others are restricted to vertical applications), and whether the obstacle is meant to be permanent or temporary.
Building of a slurry wall using cuttoff walls
Slurry walls are non structural obstacles that are constructed to impede groundwater flow. Slurry walls have been used for decades to provide cost-effective, long-term alternatives for many groundwater control and groundwater remediation problems.
The slurry wall construction technique involves excavating a narrow trench that’s kept full of “slurry” or an engineered fluid. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse.
The slurry prevents the trench by supplying external pressure which balances the inward hydraulic forces and prevents water flow into the trench from collapsing. Support is subsequently lowered in and the trench is filled with concrete, which displaces the slurry.
Slurry walls are typically built by beginning with a set of guide walls, commonly 1 metre (3.3 ft) deep and 0.5 metre (1.6 feet) thick. The guide walls are constructed on the earth surface to outline the desirable slurry trench(es) and guide excavation. Excavation is done using an unique clamshell-shaped digger or a factory trench cutter. The excavator digs down to layout depth, or bedrock, for the first cut. The trench is kept filled with slurry (usually a mixture of bentonite and water) at all times to prevent collapse.
Slurry walls are built to enclose the desired place, blocking water and softened earth from flowing into it. On conclusion of concreting, digging within the concrete wall-enclosed area can proceed. To prevent the concrete wall from collapsing into the just open place, temporary supports such as tiebacks are installed. When completed, the construction constructed within the walled-off region supports the wall, so that and/or tiebacks other temporary bracing may be removed.