When we are asked to pump concrete on site, we are generally being asked to solve a problem. “I want to construct a large reinforced concrete slab”, “I have to place concrete on the fourth floor”, “I need to get concrete into the basement of an existing building” These are typical requests, and we can solve such problems without too much difficulty or indeed much in the way of planning. However, a request in 2010 from HOCHTIEF (UK) Construction Ltd did require a little more head-scratching.
The request? To pump concrete through 100 metres of pipeline and distribute it at the end of the line. Not too difficult … until you learn that the 100 metres of pipeline took you into the middle of Backwater Channel, the waterway that empties Holes Bay into Poole Harbour. Hochtief had been awarded a contract to build Poole’s Twin Sails Bridge, an iconic scheme to link Poole to Hamworthy and open up 26 hectares of brownfield land – formerly a power station and an oil depot. The Twin Sails Bridge is a lift bridge with two triangular-shaped lifting leaves that symbolise the sails of a yacht, designed to reflect Poole’s proud maritime and industrial heritage.
The bridge has an overall length of approximately 140m with the two lifting leaves spanning 23.4m between main bearings leaving a navigable channel of 19m between the main piers. These main piers house the plant rooms including the hydraulic rams, reservoir tanks for the hydraulic fluid, pumps and other M&E plant and equipment associated with the lifting operation. It was concreting these structures in the middle of Backwater Channel that gave Hochtief pause for thought.
Early on in their planning they realised that a stationary concrete placing boom might be ideal for distributing the concrete and so brought Camfaud on board to work out the details of a suitable pumping scheme. The final scheme, agreed by Hochtief and supplied by Camfaud, was a Schwing WP1250 concrete pump, approximately 100m of 125mm pipeline (with scissor assemblies to accommodate the ebb and flow of the tides) and a Schwing SPB30 concrete boom mounted on a pile in the middle of the channel.
Using this equipment, 24 bored piles (1200mm diameter, 30m deep) were filled and both of the main piers were constructed. This work was carried out over the winter of 2010-2011 and was completed on time and with remarkably few problems considering the nature of the work and the obstacles that had to be overcome.
In addition to the bridge construction, Hochtief used this contract as a golden opportunity to invest in their employees. They had four operators trained by Camfaud for competence in the use of stationary concrete placing booms and to Construction Plant Competence Scheme (CPCS) certification for the use of trailer-mounted concrete pumps (CPCS category A44).