Cut-off wall

A cement-bentonite wall is a cast-in-situ water retaining screen, made up of a purpose-designed low-permeability material such as a cement-bentonite mixture. Driving sections such as sheet piles can be installed within the cut-off wall to reinforce the latter and assure structural stability.

Construction sequence

1. In advance construction of temporary guide walls and excavation of a trench. Filling of the trench with a cement-bentonite slurry

2. Excavation of the second panel

3. Removal of the soil located between the two previously excavated panels

4. By repeating the procedure, the formation of the cut-off wall progresses.

Fields of application

• Confine and enclose contaminated areas such as waste dumps or landfills to prevent the spread of contamination through horizontal groundwater flows.

• Drawdown or groundwater lowering to minimize water inflow or prevent undercurrent (i.e. determine quantities and zone of influence) into major infrastructural works, such as aqueducts, quay walls and access to tunnels.

Environmental impact

• Vibration-free installation

• Low noise pollution

• Removal of soil and disposal of bentonite

• The water table must be located at least 2 m below the working level

• A wide working platform for the bentonite production process and a designated storage space of a minimum of 300 m² are required.

• Workspace surface: minimal 15 m from the axis of the wall and 2 m in front of the wall

• A stable, dry and flat work platform is necessary.

Technical specifications

• Standard waterproof depths up to 35 m, occasionally seal depths up to 50 m

• Non-structural barrier: a cut-off wall has no soil retaining function so the soil itself must properly provide strength and stability.

• The water tightness / permeability and the compressive strength characteristics of the wall shall be determined by the composition of the cement-bentonite mixture, by reference to use and application.

• Possible execution with a high-density polyethylene (HDPE) plastic membrane

• Eventually reinforced with steel sheet piles to guarantee structural stability.