The real meaning of innovation
At Canary Wharf Contractors Ltd (CWCL), we take a pragmatic approach to innovation. Being innovative sometimes means doing something that has been done before, but doing it slightly differently, slightly better. Given that practice makes perfect, we believe we’re in a particularly strong position to deliver innovative solutions to construction challenges. After all, when you build 10 million sq ft of office space in seven years, you get a lot of opportunities to improve not only your specific processes, but also your overall approach to project delivery.
The Crossrail Station
Crossrail is a new rail line which will run 118 km in 2018 from Maidenhead and Heathrow in the west, through new twin-bore 21 km tunnels under central London to Shenfield and Abbey Wood in the east.
Canary Wharf Contractors are building the new station at Canary Wharf. The challenge is the station will be built in the ten metre deep North Dock of West India Quay. This provides inherent challenges that have resulted in the latest single skin cofferdam installation methods being used. To enable construction of the station box, 396 tubular steel piles measuring 18.5 metres long and 1.2 metres diameter have been hydraulically driven into the dock floor using Giken Piling machines. These piles are interlocked and provide the structure that will hold back the dock water and maintain the separation of the lower and upper aquifers by being toed into the clay layer. 31m concrete contiguous reinforced piles were then installed through the Giken tubes with 10 storey high piling cranes to retain the lower aquifer soils.
This is the first time machinery of this size has been used in the UK. This system has the added advantage of being ‘silent’ as it uses hydraulic force (not impact) to drive the piles. This methodology was environmentally essential due to the proximity of local residents and office occupants coupled with sensitive trading floors .
The Giken piling is now successfully complete and the water within the cofferdam has been pumped out enabling construction of the station concrete box structure to be completed in 2011, for receipt of the TBM,(tunnel boring machine) in 2012. The station will eventually be six storeys high suspended on 30 plunged columns, held down by 71 tension piles, 1000 piles in total when the south secant wall and North, East and West anchor piles are included, the structure being complete in 2012. Retail areas are planned for four of the six storeys between the station cores each end of the box including a landscaped, restaurant and community facility on the top floor. The station is covered by an elegant, semi open-air timber lattice roof allowing views out over the dock, Canary Wharf and beyond.
Over 98,000,000 litres of water were emptied from the cofferdam in to the dock, 150,000 cubic metres of material excavated from the dock bottom, equating to almost 300,000 tonnes. Removing this volume of material by road would of adversely affected the surrounding road network, to overcome this CWCL removed the majority of the material by river barges. Over 20,000 lorry trips were taken off East London and Essex roads over two years using this method. We re-used 50,000 metre cube of the excavated material onsite to construct flood relief schemes for the station and the retail schemes, the remainder being taken by barge to the Veolia site at Holehaven Creek. This material will help to restore the Pitsea landfill site to high quality land for conservation and controlled public access, without disturbing the nearby tidal mudflats, which are a ‘Site of Special Scientific Interest’ (SSSI).
When complete in July 2015, the station box will be 260 metres long – greater than the height of the UK’s tallest building One Canada Square – and will be between 27 metres high and 30 metres wide. Crossrail is planned to be operational in 2018.
See also: www.crossrail.co.uk
The Heron Quays Cofferdam
The construction of the Heron Quays phase of the project presented us with enormous challenges. The site was surrounded on three sides by water, with two-thirds of the fourth side also in the existing dock and the remainder comprising the existing estate. This phase of the project included three 30-storey office towers, two 13-storey office buildings, two winter gardens, a retail mall and a large parking basement. The challenge was to build it all concurrently.
Hundreds of weekly deliveries had to be scheduled and controlled. In 2001 alone, over 225,000 cubic metres of concrete and 40,000 tones of structural steel were delivered to site. This was followed by over 100,000 square metres of cladding, miles of pipe, cable and duct, as well substations, transformers, over thirty chillers and dozens of cooling towers.
Our solution was to build a cofferdam in the dock, put a road on top of it and pump out the water. Earth ramps were constructed to get traffic to the bottom of the hole for the substructures, and once the basements were constructed, delivery trucks reached tower crane pick points and materials hoists via the cofferdam roads. To keep concrete production and delivery under close control, a batching plant was built on a barge anchored in the dock.
Aggregates were delivered by barge to keep truck movements on the local roads to a minimum. Our extensive use of river traffic included sea-going barges from the continent for the delivery of large structural steel fabrications. Delivery trucks were all booked in advance and marshalled in a holding park until their allocated off-loading time, when they were called forward.
Having completed the buildings, the cofferdam was removed and the fill hydraulically pumped to excavation points for loading onto barges. Finally, the outer steel sheet pile wall was removed.
25 Bank Street and Heron Quays DLR Station
As part of the construction of 25 Bank Street and the re-development of the Heron Quays Docklands Light Rail station, CWC and its contractors developed a unique methodology for building both the 8-storey air-rights building over the railway, and simultaneously re-building the platforms and concourse below. All while the railway remained in operation.
Our solution was to erect a temporary assembly platform and two lines of runway beams running parallel to the railway over the entire viaduct. This was done during engineering hours.
The 9.2 metre trusses were delivered by barge and lifted onto the runway beams at the south end of the building in just one weekend. Next, we “launched” the trusses forward by jacking one truss forward, erecting steel infill and decking, then jacking the complete assembly forward again. This was repeated until all trusses and infill structures were in position. All while trains were passing underneath.
After the “launch” and infill phase, the level 4 deck was concreted to provide protection for the railway below, and a further 5 floors of steel and deck erected over the railway during daytime. Only the two end bays were erected at night during engineering hours.
When the steel frame and metal deck were complete, including the large level 8-9 trusses, the load was transferred from the lower level 3-4 trusses to the level 8-9 trusses, as the structure is designed to hang from level 8. The floors between levels 5 and 9 were then concreted in sequence. The system allowed all mechanical and electrical services above the station platform to be fixed and the suspended stainless steel soffit was progressively installed as the scaffold and deck was struck. This allowed maximum use of dayshift hours, whilst avoiding or minimising the impact to the railway.
The whole project was completed with no train stoppages other than planned DLR track maintenance.