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CrossRail - Europe's Largest Infrastructure Project


CROSSRAIL - EUROPE’S LARGEST INFRASTRUCTURE PROJECT

 

After years of debate, feasibility studies, planning, cost comparisons, financial options and finally government approval, the main construction work for Crossrail, Europe’s largest infrastructure project, began in 2010. Costing £14.8 billion and scheduled for completion in 2017, Crossrail will run 118 kilometres through 37 stations from Maidenhead and Heathrow in the west running through twin-bore 21 kilometres of tunnels under central London to Shenfield and Abbey Wood in the east.     

 

Since the main construction began, the Crossrail project has made good progress with work underway at all central London station sites. Tunnelling began in March this year following the assembly and commissioning of the first two tunnel boring machines (TBM), beginning the drive from Royal Oak in west London and finishing at Farringdon.

 

Prior to the arrival of the first TBMs at Royal Oak an important part of the tunnelling was the construction of the launch structure which allows the machines to propel themselves forward while steel seals, fitted around the tunnel portal entrances, are needed to support the ground during the early stages of tunnelling. In addition, a conveyor system was installed behind the TBM to remove more than one million tonnes of excavated material from the cutter head to the portal entrance. A total of 24 kilometres of conveyer belt is being used to transport spoil from the western tunnels.

Altogether, eight TBMs will be used to undertake a total of 10 individual drives to construct the 6.2m diameter tunnels under London. Each machine is 7.1m high, 140m long and weighs-in at 1,000t, without doubt a massive piece of kit. Tunnelling rate is expected to achieve around 100 metres per week. Herrenknecht, the Germany-based company was selected by Crossrail tunnelling contractors to build all the TBMs.

 

The next two TBMs were launched from the Limmo Peninsula in Docklands for the eastern tunnels this summer. Two further TBMs will begin constructing the 2.6km Thames Tunnel between Plumstead and North Woolwich during the winter and the final two TBMs will travel from Pudding Mill Lane driving towards Stepney Green and starting in 2013.

 

Five twin tunnels will be constructed including the 6.4km-long tunnels from Royal Oak to Farringdon, 8.3 km-long tunnels from Limmo Peninsula in the Royal Docks to Farringdon, 2.7 km-long tunnels from Pudding Mill Lane to Stepney Green, 0.9 km long tunnels from Limmo Peninsula in the Royal Docks to Victoria Dock Portal and 2.6 km-long tunnels from Plumstead to North Woolwich (Thames Tunnel).

 

Slurry TBMs will be used to construct the Thames Tunnel due to the chalk and flint ground conditions in this part of the capital. The remainder of the tunnels, between Royal Oak, Pudding Mill Lane and Victoria Dock Portal, will be constructed using earth pressure balance machines which will pass through ground predominantly made up of  London clay, sand and gravels. Earth pressure balance is a mechanised tunnelling method in which soil is admitted into the TBM via a screw conveyor system which allows the pressure at the face of the TBM to remain balanced without the use of slurry. This allows soft, wet, or unstable ground to be tunnelled with speed and safety. In total almost 42 kilometres of tunnels will be driven under the streets of London.

 

At the height of tunnelling, the machines constructing the western tunnels will extract 7,000 tonnes of excavated material a day. However, overall about six million tonnes of material will be excavated during the construction of stations and the twin-bore tunnels. According to Crossrail close to 100% of this excavated material is expected to be clean, uncontaminated and reusable elsewhere.

 

Each of the TBMs is being operated by tunnel gangs working in shifts. A gang comprises approximately 20 people with about 12 on the TBM itself and eight working between the rear of the machine and the tunnel entrance. The TBMs operate 24/7 only stopping for scheduled maintenance.

 

Prior to tunnelling, a concrete segment manufacturing plant was opened at Old Oak Common in west London, producing the 250,000 concrete segments needed to line the Crossrail tunnels. The plant houses 216 moulds and is capable of making 200 segments per day at peak production. Approximately 60 people are employed on-site.  The plant has been built specifically for the production of Crossrail tunnel segments and once tunnelling is complete, it will be removed.  Another plant has been built at Chatham in Kent to supply segments for the eastern tunnels between Docklands and Farringdon

During Crossrail's construction, more than 85% of all excavated material will be transported by rail or water including the 4.5million tonnes destined for Wallasea Island located at the mouth of the river Crouch in Essex where it will be used by the Royal Society for the Protection of Birds (RSPB) to create a major new 1500 acre nature reserve. This project aims to combat threats from climate change and coastal flooding by recreating a wetland landscape. It will also help to compensate for the loss of similar tidal habitats elsewhere in Britain due to rising sea levels.

 

Before the excavated material could be transported, rail sidings and a £13.5 million freight link from the North Kent line had to be constructed to allow freight trains to access Westbourne Park so that the excavated material could be transported to the former Lafarge cement works at Northfleet from where it will be shipped to Wallasea Island.

When the sidings and link were completed, the first 13 wagon train left Crossrail’s Westbourne Park site for Northfleet after it was loaded with 492 tonnes of earth during May. Two trains a week are also running a return journey between Crossrail’s tunnel entrance near Paddington and Northfleet. The trains will eventually increase in size to 27 wagons and run three times a day. At the peak of tunnelling up to five freight trains a day will operate from Westbourne Park carrying a total of 7,000 tonnes of earth. According to Crossrail, transporting the excavated material from the western tunnels via train and ship has removed at least 50,000 lorry journeys from central London.

Excavated material from the eastern running tunnels will be loaded onto ships directly from the tunnel conveyor surfacing at lnstone Wharf on the Bow Creek. However, material arising from shafts and stations will be brought by road to Crossrail's docklands transfer site at the Barking riverside jetty.

 

Up to five ships a day will transport excavated material down the River Thames to Southend-on-Sea. They will then travel north passing Foulness lsland before turning west into the River Crouch to reach Wallasea lsland.

 

WALLASEA ISLAND

 

A key part of the project is the unloading facility at Wallasea Island. Here contractor Bam Nuttall and partner Van Oord UK won the £50 million contract to ship the material, construct the pontoon jetty and install the unloading and conveyor systems. On-site work commenced in September but suspended the following month as work was restricted due to the bird nesting season but then resumed in April this year when piling began.

To install the restraining piles for the pontoon and to support the conveyor system the company hired a BSP heavy-duty CG210 hydraulic piling hammer fitted with a 14t dropweight from BPH Equipment. The hammer was pedestal-crane suspended and powered by an-onboard power pack. Headquartered at Barton on Humber, BPH Equipment is the UK’s leading crane and piling equipment rental specialist. The company owns an impressive portfolio of impact and vibrating piling hammers together with a fleet of modern crawler cranes ranging in capacity from 50t up to 250t which are available for hire or rental on both short and long term contracts.

The foundation and restraining piles were transported by sea to the site consisted of 48 tubular steel piles, 30m in length and 450mm in diameter which were driven into stiff clay ground conditions. Additional piles 37m long, 1092mm in diameter and a thickness of 40mm were also driven by the BSP hammer. Although the exposed site is subjected to adverse weather some delays were inevitable during construction due to strong easterly winds.         

To form the jetty BAM Nuttall brought-in two floating pontoons, each 15m wide and weighing 800 tonnes, which have been joined to form a temporary 180m long jetty with a 1,000m2 deck area. A hopper and a crusher have also been integrated in the on-board conveyor system.

Four Terex Fuchs wheeled MHL 360E materials handlers are being used to unload the ships as they arrive at the jetty. Two 90 metre, 2500 tonne ships can be unloaded at the same time with up to five ships a day arriving at the site  At peak time, two machines per pontoon will service four ships and unload some 10,000 tonnes of material over a 24 hour period.

Each of the Terex Fuchs wheeled machines are equipped with 9.7m long booms, 7.8m dippersticks and 0.6m3 capacity clamshell buckets and have an operating weight of between 44t and 46t.  Power is derived from a turbocharged Deutz diesel engine delivering 186kW. Features include a hydraulic-lift cab with large, panoramic windows to provide the operator with an excellent eye-level view of almost 6m from the pontoon deck. A dual circuit hydraulic system allows the machines to slew rapidly during each unloading cycle as well as allowing precise control and manoeuvring in the confines of the jetty deck. The machines are fitted with independently controlled front and rear stabilisers.   

Electricity to power the facility is being brought by underground cable from a mains source one and half miles away while three 400KVa generators provide a back-up supply in case of a power failure. One of the generators is constantly on stand-by.  

Excavated material is unloaded directly from the ship into a hopper and crusher and then on to an 800 metre long conveyor system which transports the material within the site. The conveyor stretches from the jetty to a holding point for the spoil, from which it will distributed around the site by truck. To accommodate tidal movements of up to six metres, the conveyor comprises a flexible section on the pontoon connecting to a fixed shore section to allow for the tidal range.

The RSPB nature reserve on Wallasea Island will be one of the largest new wetland nature habitats in Europe, providing an environment specifically tailored for fish, reptiles, insects, mammals and birds and acting as a tourist attraction and recreational resource for local people.

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