WET News

WN May 2015

Water and Effluent Treatment Magazine

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drainage 18 WET NEWS MaY 2015 river water extracted by the pumps was then fed into a high pressure water pump to supply motive water to the Jet Pump hopper located on the shore In order to drain the area of the river bed where the founda- tions for the first tower were to be constructed, a steel coffer dam was erected. This was designed to isolate the site and allow the construction team to excavate down to the river bed safely, ready for piling and con- crete pour. Circle of steel However, before excavation could begin, the coffer dam had to be made sufficiently robust to resist the weight of the water in the river and the force of its flow. The coffer dam consists of a circle of steel sections that were driven into place to create a cir- cular dam with water inside and out. The additional strength required was then provided by sand that was pumped into the dam at high pressure, using water from the river itself to cre- ate the necessary force. Specialist contractor Jet Pumps UK used pump hire spe- cialist Sykes Pumps to provide two 8" submersible pumps to aid the sand filling operation for the first coffer dam. An access bridge was constructed between the shoreline and the coffer dam and the submersible pumps were suspended from this tem- porary structure to extract water from the river. River water extracted by the pumps was then fed into a high pressure water pump to supply motive water to the Jet Pump hopper located on the shore to fluidise the sand ready for pumping into the centre of the coffer dam. Sand sludge Explains Graham Lamond from specialist contractor Jet Pumps UK: "We needed to create a sand sludge to fill the coffer dam and the most efficient way to do that was to use the river as the water source because it was readily available on site and would be pumped back into the river as part of the process. "The two 8" submersible pumps were ideal for this pur- pose due to the rise and fall of the tide, but we also needed a further high head hardened steel diesel pump, the UVO 200/150F (D70) from Sykes Pumps to drive the sand sludge from the Jet Pump hopper and down the 250 metre pipe to the dam." Sykes Pumps provided 8" submersible pumps to extract water from the river and fed it through another high-head pump to boost the jet pressure from the hopper. This technique enabled Jet Pumps to increase the pressure from two/three bar to nine bar, enabling the sand to be pumped into the coffer dam at the rate of 100 tonnes per hour. Lamond continues: "The cof- fer dam for the first tower meas- ures about 40 metres across and sufficient sand had to be pumped in to create a com- pacted sand centre that could be excavated. "The pressure boost that the UVO 200/150F (D70) from Sykes Pumps provided enabled us to complete that part of the opera- tion within just four days, including night works, so that the construction team could get on with the rest of the operation." Sykes Pumps provided both the pumps required for the The operation was completed within just four days, including night works The two 8" submersible pumps were ideal for the project because of the rise and fall of the tide

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