Divers called in for underwater concreting job

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Mixamate recently provided concrete for a unique job in South Quay Plaza, Canary Wharf, in which professional divers were used to assist in the laying of underwater concrete. The technique, which uses fabric formwork socks to place mixes into underwater areas, allowed GPSM DiveCo Ltd. to install cofferdam stop-ends into the Quay wall structure.

We chose Mixamate as they were able to provide us with the complete package from providing the grout through to cleaning the pump and removing waste” said Alex Smedley, Site Supervisor at South Quay Plaza for DiveCo. “Less personnel were required on site who would normally be mixing and operating the grout pump. For those that were needed, the health and safety risk was reduced due to not needing to handle COSHH materials directly, as it was all mixed internally on the lorry.

6m3 of a special concrete mix were used to fill fabric formwork vertical socks that created temporary grouted stop-ends between an existing quay wall structure and a new sheet piled wall for the creation of a cofferdam. The grout sock was lowered into a vertical steel recess against the existing wall, with a maximum gap of 350mm at the top and a 135mm at the bottom. The cofferdam seals were then filled with a highly fluid sand-cement micro concrete, to form a near watertight seal between the existing quay wall and the steel sheet piles, which in turn allows works to continue on the quay wall.

Due to the installation process taking place predominately underwater, professional divers are used at several points during the project. Initially this is to survey the existing wall structure and remove any snag or tearing risks, then to check the grout sock for folds and correct alignment. The divers are then used again during the grout pour to monitor fill levels report any leaks in order to minimise environmental impact.

The Mixamate All-in-One Concrete Pumping Truck provided the perfect machine to assist in this delicate job, since it provides the delivery, mixing, and pumping of materials from a single vehicle, and can run a pumping hose of up to 100m that allows us to assist in the most intricate of sites.

Rather than having multiple vehicles delivering and collecting from the site it was in fact just the one trip, which reduced our carbon emissions. Also, as Mixamate could provide us with the exact amount of grout we required and any that was left unmixed was not charged, this saved money and helped to eliminate waste.

“They provided a highly efficient grout pump that they themselves delivered, operated and took away to clean. This saved on man hours and reduced operational planning because when the pour was complete, we could carry on with the project rather than stopping to wash down the area and clean all the equipment. The staff were friendly, knowledgeable, efficient and provided us with outstanding service. We would definitely be using them again and would recommend them to others.”

This was a great project to be involved with and we were interested to see such an innovative approach being taken to come up with a solution for effective underwater concreting.

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