A diaphragm wall is a cast in place steel reinforced concrete wall which is typically used for the construction of deep basements in urban environments where the ground water level is high. As other earth retaining structures (such as secant piles or sheet piles) it prevents the ground water to flow in the excavation and resists the pressures exerted by the soil, water and adjacent structures. The slurry diaphragm walls can be supported by struts or ground anchors, or by slabs in the case of top-down construction.
To assure the linearity of the wall are constructed guide beams. Individual panel lengths are determined by a number of factors including trench stability and the sensitivity of the surroundings to movement. Typically they do not exceed 7m in length, while they can reach 50m in depth. The wall can be constructed very close to existing structures while special measures can be undertaken to avoid their damage. Trenches are held open during excavation, so that reinforcement and concrete can be constructed, by the use of bentonite slurry which forms an impervious deposit (cake) on the walls of the trench, isolating the hydraulic pressure of the slurry from the surrounding soil and ground water, such that this pressure exerts sufficient outward force to keep the trench open. When excavation of a panel is complete, special vertical steel profiles are introduced between the joints of adjacent panels, and the bentonite slurry is desanded to assure the quality of the concrete. Finally, steel reinforced cages are lowered into the trench and the panel is concreted (tremie method) while the slurry is withdrawn and recycled. Spacers are used to ensure sufficient concrete cover on the cage.
Throughout the years the construction of slurry walls has undergone many improvements which only makes them much more efficient and a significant part of geotechnical engineering. Please contact us for more details.
In the last years our personnel has been involved with the construction of more than 80.000 square meters of slurry diaphragm walls, with depths between 15 to 40 meters and thicknesses between 60 and 100 centimeters. Also, we have been involved with the construction of 4 top-down projects where depth of excavation ranged between 13 to 16 meters. Projects involved residential and office buildings, as well as, railways and subways within urban and interurban environment.