A kilometre-long stretch of mud and machinery forms the worksite leading up to the Royal Oak Crossrail portal as T&TI visits in February. As narrow as 20m in places, conditions are tight, with single-file walkways in places. The A40 flyover juts out along the north of the site and surface rail skirts along the south.

As the visitors are lowered by cage lift from the site office near the flyover, the roaring noise turns out to be coming from a skate park echoing off the underside of the elevated road.

The first machine is nearly assembled and waiting to be taken away from the Westbourne Park site (the west end of the worksite), through the Royal Oak eastern end of the site, and towards the Royal Oak portal at the extreme east.

The BAM Ferrovial Kier (BFK) JV’s workforce is 100-strong and began site preparations in November 2011. The contract award for the 6.2km western tunnels from the Royal Oak portal to Farringdon was announced in December 2010 along with a contract for access shafts and SCL work at Tottenham Court Road and Bond Street. The combined value was GBP 500M (USD 787M).

The machines
The Herrenknecht TBM set to execute the first drive for the Crossrail project is approximately 85 per cent assembled says Derek Whelan, BFK shift manager. "The cutterhead itself is about 99 per cent complete. We’re on target to kick off on 21 March with no delays expected.

"We’ll move the first TBM down to the tunnel eye on 16/17 March over a period of 24 hours. The second machine should be fully assembled by the end of March, with transition to the portal on 14 April and a launch towards the end of that month. There’s a four-week stagger on the two drives."

Mammoet was contracted to move the machines to the tunnel eyes via 500t cranes. Whelan and BFK tunnel agent Alfonso Chicharro point out a small bridge that runs overhead and perpendicular to the route the TBM must take from the back of the site to the portal.

Mammoet will raise the bridge on jacks for around 10 hours at a time. The jacking forces required are not particularly large.

The TBMs themselves are 7.1m EPBMs. Once lined, the Crossrail running tunnels will have a 6m internal diameter. During a visit to the Herrenknecht TBM factory in Schwanau, southwest Germany in December, Ralph Lickert, a Herrenknecht project manager for Crossrail told T&TI, "This is a very compact machine. You can see from walking through it that there isn’t much room. It is also very powerful with over 55,000t of thrust and a high main drive torque [of 9,800kNm].

"The belt scales are also of the highest achievable quality and are provided by [Australia-based] Control Systems Technology which was the only company able to meet the requirements."

The machines are expected to carry out a 100m+ advance each week, removing 20,000t of spoil in the process.

New regulations
British standard 6164:2011, clause 14.12 requires refuge chambers in UK tunnel projects. The 2011 update is applicable to this project. Donald Lamont, principal of Hyperbaric and Tunnel Safety and member of the Crossrail Engineering Expert Panel says, "The standard does not directly address TBM safety but does so through reference to EN 12336, which is the current CEN standard for TBM safety. EN 12336 is to be replaced in due course by prEN 16191 – the draft revised CEN standard for TBM safety, which will require a refuge chamber on a TBM.

"The Crossrail TBMs are not the first in the UK with chambers – the Lee Tunnel TBM has one. ITA Working Group Five is also preparing guidance on the specification for refuge chambers – their equipment duration and so on."

Update and schedule
On 22 February a Crossrail spokesman announced that the first machine had been completed. Andrew Wolstenholme, Crossrail chief executive adds, "The first Crossrail TBM is due to undergo testing ahead of the start of tunnelling. Work is underway to assemble the second TBM."

Wolstenholme adds that following the second TBM launch in April, "later this year a further two TBMs will be launched from Limmo Peninsular in the Royal Docks that will travel a total of 8.3km (westwards) towards Farringdon via Canary Wharf, Whitechapel and Liverpool Street.

"Towards the end of 2012 another two TBMs will begin construction of the south-east section of the route, launching from Plumstead portal in the south-east and travelling a total of 2.6km to construct the Thames Tunnel."

Managing manpower
The drives from Royal Oak to Farringdon will advance in a two on, one off three-shift pattern with 12 hours to a shift. Crossrail’s western tunnels project manager Andy Alder says, "The important thing is managing fatigue. You can do this if you know where people live and can make sure they are not travelling a long distance before and after working, and that is what we are doing here.

"Some people in the industry have given the opinion that you should run eight hour shifts rather than 12. The simple fact is that there just aren’t the manpower resources in the industry for eight hour shifts unless you take on less experienced people."

Moulds, segments and production
The BFK JV is supplying its own segments for the western tunnels at a new purpose-built factory at Old Oak Common in west London. The factory will be replaced by a major Crossrail depot upon an end to production in spring 2013.

Bob Wagstaff, BFK segment factory manager, says, "After this we have a duty to get maximum value from the moulds. We will try to find a comparable diameter project for this, but the industry is not always the best at learning from itself – we will probably find a job that is 0.05m out."

It was incredibly cold on site as production began in the first week of February. During the night following T&TI’s visit in the second week of the month, teams say they are preparing for temperatures as low as -5ºC.

Wagstaff explains mould selection: "A carousel system brings the sides up and the middle down. Once it’s out of the curing chamber at 60ºC you have to look after the segments, and you just can’t do that in this cold. With our static moulds, all of the segments are perfectly within tolerance."

Wagstaff adds, "We have a seven minute cycle time and it is 18 hours before we de-mould normally, though a bit extended due to the cold. Strength is 30N at 24 hours and easily 20N after 18 hours. We reach 58N after seven days."

In total 213 moulds have been manufactured by CBE for the project. Segment stockpiles need to be maintained at six weeks of the consumption due to tunnelling rate. Wagstaff estimates this will be approximately five or six hundred rings, but that they will probably exceed this and reach the 2,000 to 2,500 stockpile capacity of the site.

Segments are in a seven plus key arrangement. They are tapered, and moulds colour coded with red moulds producing right segments and blue for left. An internal micrometer is used to check the width of moulds and depths are checked by vernier scale. Segment width and depth is also checked by vernier.

EPDM gaskets are used, with combined hydrophilic in some areas.

Scissor lifts are used to lift the segments. Wagstaff says that he favours this method over vacuum, which he views as time consuming and that he likes to "keep the operation as simple as the team can make it". The cost of all moulds, lifting and turning gear from CBE was EUR 3.6M (USD 4.84M). Each mould has an identifying code that is cast onto every segment. The date is sprayed next to this giving each segment a unique identity.

The mix
"The basic concrete mix is based on the High Speed One specification," Wagstaff tells T&TI. "But it is a stricter specification – it’s High Speed One and a little bit more. We are using a limestone aggregate and 40kg of powder in a 70/30 ratio. Some 30kg/m3 of Dramix steel fibres with hooks go into the mix and an increase of polypropylene fibres was required – 1.25kg/m3 passed the fire test."

A BFK spokesman said 1-2kg/m3 of Propex poly fibres were used. Bekaert manufactured the batching plant, which has a planetary mixer system.