Seeing red - bentonite plants popping up around the City
Large red silos have started popping up around the city to help build the foundations of our City Rail Link train stations.
The silos are part of the Link Alliance’s bentonite plants, which create and recycle bentonite slurry - a wet clay that is pumped into the holes created by piling rigs to stop them collapsing before the concrete is pumped in.
Plants were being assembled at our Aotea and Karangahape Station sites in late May, with a third plant expected at the Mt Eden site in late August. City dwellers might also remember previously seeing a red plant around our Britomart construction site as pictured above. The silos from Britomart are being reused at the Karangahape Station site.
The bentonite plants are needed for the below ground construction of the station’s concrete walls, known as diaphragm walls (D-walls). A D-wall is a continuous wall constructed in the ground, typically to form an underground barrier or structure.
The clay is pumped into the excavated area to keep ground water out, maintain positive pressure, and prevent the trench from collapsing until steel reinforced concrete can be added in its place. The bentonite is continuously pumped through the excavated area and back through the plant to screen out dirt and other material prior to re-use.