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GLEESON GRABS A QUICK SANDWICH
00:00 23 Feb 1995
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Southern Water Services' solution to the need to clean up Ramsgate,
Sandwich and Deal beaches to EC standards is the œ56 million
Sandwich Bay scheme, a high priority project which eliminates 11
short sea outfalls.
The scheme involves creation of some 5,500m of stormwater tunnels and pumping stations. Up to 860 litres/second will be pumped to the scheme's treatment works, the new Weatherlees Hill wastewater treatment works.
A high-speed turnkey contract by MJ Gleeson is due to complete the plant for handover next April, less than two years after work began on the greenfield site.
The contractor makes no secret of its belief in the design and build approach. 'Doing more ourselves is the way to keep control,' said Bob Jukes, director of Gleeson's Southern Construction Division. 'It gives us more flexibility.'
Gleeson produced its own alternative design which won the contract. By reorientating the site layout, it was able to eliminate a final settling tank and reduce the aeration tanks, producing substantial savings in the contract price.
The contract is a version of the IChemE Green Book extensively modified by the client. Gleeson has now had several years' good experience of such contracts with other clients and this helped establish a similar rapport with Southern Water Services. However, the contractor believes the speed of construction speaks for itself. 'You would never build this plant as quickly with a conventional contract,' said Jukes. 'It would have been 12 months longer.'
He says such contracts give both parties an incentive to solve problems. With all design (including M&E works) controlled in-house, the risk of delays in one area holding up work in another can be managed out.
Steel fixing apart, virtually all labour on site is Gleeson employees working under the general foreman. The company believes the advantages outweigh any losses from not sub-contracting the work.
The plant's equipment is bought from suppliers and the contractor's own M&E engineers manage its installation. Cables are laid by its own electricians. Even the requirement to protect ductile iron pipes with a winding of bitumen impregnated tape is done not at the factory but on site by the contractor's site developed apparatus.
The approach explains the presence of an Elba 30 batching plant on site although, with a total concrete requirement of around 15,000m3, this is only just at break-even point. But it allowed considerable precasting on site, avoiding the need to purchase expensive proprietary items like primary settlement tank sumps. The aeration tank bridge and baffle walls were also precast on site, with items even cast for other sites.
The use of steel shuttering has given a very smooth finish to in-situ concrete items such as settlement tanks. Steel shuttering was fabricated for both primary and final settlement tanks, which were both designed with the same 30m dia to minimise the shuttering needed. This will now be available for future such castings at other sites.
The plant's treatment technology is a fairly conventional fine bubble activated sludge process. Effluent will first be screened in an inlet building with full odour control. It will pass via a detritor to four primary settlement tanks (seven hours' retention at dry weather flow) and then be pumped to the four 4.5m deep aeration tanks where air is pumped from the adjacent blower house.
The liquid then gravitates to four final settlement tanks (10 hours retention at dry weather flow) before passing through a flap valve to the 500m outfall into the tidal River Stour.
An environmental challenge was cutting the outfall across an SSSI which meant careful replacement of topsoil and vegetation after laying the 1100mm diameter ductile iron pipe.
Gleeson created extensive savings with the piling system created in its redesign. Continuous flight augured piles were used on the structures and the large piling platforms required were constructed using imported hard core.
Pile layouts and loadings for the concrete tanks were redesigned and the 1,700 originally proposed reduced by around a third. Tank bases were redesigned too.
One major uncertainty was Southern Water Services' sludge strategy which is still undergoing development but which necessitated a change from sludge thickening to sludge pressing in mid-stream.
The scheme involves creation of some 5,500m of stormwater tunnels and pumping stations. Up to 860 litres/second will be pumped to the scheme's treatment works, the new Weatherlees Hill wastewater treatment works.
A high-speed turnkey contract by MJ Gleeson is due to complete the plant for handover next April, less than two years after work began on the greenfield site.
The contractor makes no secret of its belief in the design and build approach. 'Doing more ourselves is the way to keep control,' said Bob Jukes, director of Gleeson's Southern Construction Division. 'It gives us more flexibility.'
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Gleeson produced its own alternative design which won the contract. By reorientating the site layout, it was able to eliminate a final settling tank and reduce the aeration tanks, producing substantial savings in the contract price.
The contract is a version of the IChemE Green Book extensively modified by the client. Gleeson has now had several years' good experience of such contracts with other clients and this helped establish a similar rapport with Southern Water Services. However, the contractor believes the speed of construction speaks for itself. 'You would never build this plant as quickly with a conventional contract,' said Jukes. 'It would have been 12 months longer.'
He says such contracts give both parties an incentive to solve problems. With all design (including M&E works) controlled in-house, the risk of delays in one area holding up work in another can be managed out.
Steel fixing apart, virtually all labour on site is Gleeson employees working under the general foreman. The company believes the advantages outweigh any losses from not sub-contracting the work.
The plant's equipment is bought from suppliers and the contractor's own M&E engineers manage its installation. Cables are laid by its own electricians. Even the requirement to protect ductile iron pipes with a winding of bitumen impregnated tape is done not at the factory but on site by the contractor's site developed apparatus.
The approach explains the presence of an Elba 30 batching plant on site although, with a total concrete requirement of around 15,000m3, this is only just at break-even point. But it allowed considerable precasting on site, avoiding the need to purchase expensive proprietary items like primary settlement tank sumps. The aeration tank bridge and baffle walls were also precast on site, with items even cast for other sites.
The use of steel shuttering has given a very smooth finish to in-situ concrete items such as settlement tanks. Steel shuttering was fabricated for both primary and final settlement tanks, which were both designed with the same 30m dia to minimise the shuttering needed. This will now be available for future such castings at other sites.
The plant's treatment technology is a fairly conventional fine bubble activated sludge process. Effluent will first be screened in an inlet building with full odour control. It will pass via a detritor to four primary settlement tanks (seven hours' retention at dry weather flow) and then be pumped to the four 4.5m deep aeration tanks where air is pumped from the adjacent blower house.
The liquid then gravitates to four final settlement tanks (10 hours retention at dry weather flow) before passing through a flap valve to the 500m outfall into the tidal River Stour.
An environmental challenge was cutting the outfall across an SSSI which meant careful replacement of topsoil and vegetation after laying the 1100mm diameter ductile iron pipe.
Gleeson created extensive savings with the piling system created in its redesign. Continuous flight augured piles were used on the structures and the large piling platforms required were constructed using imported hard core.
Pile layouts and loadings for the concrete tanks were redesigned and the 1,700 originally proposed reduced by around a third. Tank bases were redesigned too.
One major uncertainty was Southern Water Services' sludge strategy which is still undergoing development but which necessitated a change from sludge thickening to sludge pressing in mid-stream.
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