This winter has seen flooding hit the UK once again as heavy rains and gale force winds have battered the country. The good news for residents of Maida Vale in northwest London is that from December 2014 sewer flooding will become a thing of the past. "We are disconnecting every property that floods from the existing sewer and redirecting the flow to two new pumping stations," explains Iain Tytler project manager for Optimise.
Optimise is a joint venture between contractor J Murphy & Sons, Barhale Construction, Clancy Docwra and consultant MWH and is carrying out the work as part of its AMP 5 framework agreement with the UK’s largest water company Thames Water. "In dry weather all sewage will be pumped away immediately, in storm conditions the pumping station will hold the runoff and then we have storm pumps to take the flow away once the rain has subsided."
The works will tackle two major sites of sewer flooding situated approximately 0.75 miles apart that are hardest hit during summer storms where large volumes of rainfall land in a short period of time. "We are removing 177 properties from the sewer flooding database but we think there are up to 350 properties that have been flooded. There hasn’t been any flooding here for four years but prior to that there were three flood events," says Tytler.
The 15 month project will see the placement of 1,600m of pipe and two new major pumping stations at Tamplin Mews and Westbourne Green giving an additional 8000m3 of stormwater capacity. Given that these are situated in much valued green spaces the infrastructure is below ground as much as possible and above ground kiosks are to be constructed in timber to fit in with the park environment. Hexpath grids are being used as ground reinforcement along the vehicle access route as these allow grass to grow within it and retains the green space.
In total 1,180m of the new sewer pipe will be placed using trenchless construction methods and 420m using traditional open cut. Pipejacking of a crucial 98m section that links the new sewer to the Tamplin Mews pumping station began in November 2013. "The pipejacking ranged from 8m to 10m deep and was running parallel with the road and adjacent to an existing network sewer. The depth and size of the bore made microtunnelling the best solution," says John Raftery, site manager for Optimise. Work began with the sinking of the launch and reception shafts. "The shafts were sunk as 5m underpinned segmental shafts. The drive shaft was underpinned to about 18m and then we had to backfill that up about 5m. The reception shaft was built in exactly the same way and sunk to 10m," says Raftery. There was also a lot of utility diversion to undertake including gas pipes, water mains and power and telecoms cables. After around three weeks constructing the launch pit the team could begin setting up the pipejack. "We constructed the needle for the temporary breakout and built the back thrust wall, and then we got the above ground equipment set up for the microtunnelling and that consisted of the electricity generator, control unit, and a separation plant for cleaning the slurry," says Raftery. Boring was carried out using an Iseki TCC slurry machine supplied by Barhale. This was followed by the jacking in of 1000mm precast concrete pipes from FP McCann. "There were no major issues. Ground conditions were very stiff clay and the pipejack progressed as expected," says Raftery.
The 98m section took 10 days to complete was followed by two days of grouting the pipework. By the end of November the section was complete and the team is now constructing more of the upstream sewers utilising the Guided Auger Boring technique.
By October 2014 Optimise plans to have completed the pipework, 2014 will also see the construction of a 400m long section of 2.44m ID tunnel which will transfer flows to the 25m deep 20m diameter pumping station in Westbourne Green and all work is set to be completed by the end of the year
