Rostock, Holzhalbinsel district – The sky is blue on this July day. On the construction site right next to the Warnow River, a hotel is being built in a prime location. Four house-high silos glow bright yellow and white in the sun. They store Bentonite suspension, the supporting liquid used to carry out diaphragm wall work in the ground before the completed diaphragm wall is concreted from the bottom up.
ZÜBLIN Ground Engineering used this method to create a 17-metre-deep reinforced concrete wall around the foundation soil. Alexander Stehle, Senior Foreman at ZÜBLIN, North-East Division, walks with quick steps to a seemingly inconspicuous container. Inside lies the heart of an innovation that has led to a sustainable and cost-saving solution on this construction site: a centrifuge. “With this we manage to reprocess the bentonite suspension”, says Stehle. And not just once, but several times. What remains after each cycle is spadeable material that is much easier to remove, and water that can be disposed of as normal wastewater.
“Previously, we could rarely reuse the bentonite suspension, and at the end of each project the solution had to be disposed of at great expense”, he says. By using the centrifuge and a sophisticated mix of flocculants, the bentonite is now almost completely processed for further use in the Rostock project. The bentonite suspension can be reused during the entire construction of the diaphragm wall. This has not only reduced disposal costs but also saved large quantities of the starting materials. “It really worked out great”, says Stehle. “It really saved us a lot of money.”
Another innovation in Ground Engineering
Another innovation in the handling of bentonite suspensions was tested by ZÜBLIN Ground Engineering on the construction site in Rostock. Read here what the Airlift/Mammoth Pump project is all about..
This method, used by a team from STRABAG BMTI (Ronny Schlieder) and ZÜBLIN Ground Engineering (Clemens Mairhofer), is used to pump suspensions containing solids. At high pumping heights, standard pumping technology has design-related application limits; in addition, these liquids can block and wear out the pump wheels of wastewater pumps.
In the so-called mammoth pump used in the airlift process, compressed air is pumped into the delivery pipe. Due to its lower density compared to the surrounding suspension, the mixture of air and suspension in the delivery pipe creates an upward flow that transports the solids at the bottom of the suction pipe upwards. The simple and inexpensive process significantly minimises wear and tear on the construction site, especially in projects with diaphragm walls and suspension-supported piles. During the test in Rostock, the otherwise inevitable clogging of the system was completely avoided; in fact, the pumping performance was so good that the employees at the pump got an unwanted shower.