14 NEW CIVIL ENGINEER 01.03.12 | www.nce.co.uk

COVER StORy: TOTTENHAM COURT ROAD UNDERGROUND

Getting Tottenham Court Road Tube station in central London fit for purpose for modern day

London Underground passen-ger demands and ready for the onslaught of passengers from the new Crossrail line is unques-tionably a massive task.

Over 150,000 people use the station every day, and passenger numbers are expected to surge to 200,000 with the opening of the Tottenham Court Road Crossrail station in 2018.

At present the station is an interchange between the Northern and Central Lines. The congestion relief scheme in-cludes an upgraded and enlarged ticket hall, three new entrances, additional escalator access to the Northern Line platforms, improved circulation space, step-free access throughout and an interchange with Crossrail – including the construction of the eastern ticket hall box. A separate contract will build the Crossrail station platforms and a western station box.

The works at Tottenham Court Road take place in a very busy part of London. The site is on the junction of Oxford Street, Charing Cross Road and Tottenham Court Road – a not insignificant intersection. Tube trains must run, uninterrupted throughout.

And make no bones about it. This is a massive project for London Underground (LUL) and the contractor, and the whole project team is under in-tense pressure to deliver; LUL’s case for future funding hinges on it.

So critical is the project that LUL capital programmes director David Waboso drops in on NCE’s visit to highlight its importance.

“The cost – £480M – is macro-economic stuff when everyone is fighting for funds. We have got to start talking about what we need in the next funding round soon, and you don’t get a seat at the table if you’re not deliver-ing,” he emphasises “And that’s what this team is doing.”

Critically then, the project remains on schedule and within budget. And equally critically, after an eight month closure, the Northern Line platforms were returned to service on schedule on 28 November 2011.

“A really big deal for us was reopening the Northern Line platforms,” stresses Waboso. “We said we’d do it in seven months, and we did.”

It was a Herculean 24/7 effort by joint venture contractor Taylor Woodrow/Bam Nuttall (TWBN). “At the time we would have had over 450 people work-ing 24/7,” says TWBN project director Jez Haskins.

On such a massive and com-plex job it is hard to pick out the most important achievements, but completion of the Northern Line platform work has to be up there. The platforms are in adjacent, closely aligned tunnels, and had to be closed so contrac-tors could reprofile the curved walls in certain areas to make room between them for a new access passage. This will lead to a new escalator box and will pro-vide additional platform access points for passengers moving to and from the new ticket hall being built above them under Tottenham Court Road itself.

During the works, which started in April 2011, long lengths of the platforms’ con-crete, plaster and tile finishes had to be removed to expose the curved iron segments that sup-port the tunnel. These then had

The £480M upgrade of Tottenham Court Road Underground station is possibly one of the most fiendishly complex schemes ever tackled in the capital. Yet it is on time and on budget. Mark Hansford reports on a pretty impressive construction effort.

UndergroUnd SenSation

“the cost – £480M – is macro-economic stuff when everyone is fighting for funds. We have got to start talking about what we need in the next funding round soon” David Waboso, LUL

■ 2007 Utility diversions commence.

■ 2009 Buildings on Charing Cross Road purchased and demolished.

■ 2010 Main construction work begins with construction of a continuous underground wall. This will create large new spaces that will form the upgraded station.

■ 2011 Northern Line platforms closed for eight months to allow the tunnels to be reshaped. A temporary railway was built along the platforms to allow plant and materials to be transported to the working areas.

■ 2012 Construction of new underground structures: tunnels, the new ticket hall and Goslett Yard box.

■ 2015 First new station entrance opens

■ 2016 Tube station completed.

■ 2018 Crossrail services begin.

TIMELINE OF WORKS

NEW LOOK: TOTTENHAM COURT ROAD

New high capacity entrances

Expanded Tube ticket hall

New Central Line access

Existing Central Line

Existing station infrastructure

Existing Northern Line

New Northern Line access

New Crossrail infrastructure

Ticket hallbox under

construction

Central Linecongestion

relief tunnelssecondary lining

being installed

FutureCrossrail 2access

Central Lineplatform bridgesto be built

Goslett YardCrossrail station box

under construction

New Northernline access tunnelunder construction

New Northernline access escalatorbox complete

Oxford Street

Centre PointTower

SITE

New Oxford Street

Charing Cross Rd

Tottenham Ct Rd

High Holborn

0 40m

New high capacity entrances

www.nce.co.uk | 01.03.12 NEW CIVIL ENGINEER 15

to be replaced with vertical steel ones that would release space behind the platform wall – free-ing up room for escalators and an access tunnel to be built later. In total, iron segments from 195 rings in the station tunnel lining have been replaced with over 1,000t of brand new, specially manufactured tunnel segments.

That the work was completed on time staggered many – not least London’s Evening Stand-ard, a paper never shy to stick the knife in where the Tube is concerned.

But that’s far from all that has been going on. In the last year alone the list of different types of construction work completed by TWBN is staggering. As well as the work on the Northern Line platform tunnels it has also ex-cavated a 30m deep box for new Northern Line escalators.

Across the site to the west, the contractor has also excavated over 130m of new station inter-change tunnels for the Central Line. These will provide more than one access point to the Central Line platforms, and will allow passengers to interchange with Crossrail services deep underground.

Between these two work sites it has also driven more than 800 secant piles and a host of diaphragm walls to form new underground spaces – mainly for the massively expanded sub-surface ticket hall that is ef-fectively a giant basement.

And, in the south western corner of the site, it has driven in large plunge columns for Crossrail’s eastern station box – the largest of this type ever built in the UK.

LUL programme manager Les Hamilton’s understated opinion says it all: “TWBN JV is per-forming well on the Tottenham Court Road Station upgrade project, achieving all milestones in a very challenging environ-ment” he says.

How? “LUL and TWBN make very good use of early warnings/risk reduction meetings to en-sure that problems are resolved quickly in a non-adversarial way to keep the focus on delivering the works to schedule,” he says.

Haskins agrees. “I am sur-prised at how few unexpected things have been found. The biggest thing is that it is a com-plicated, logistically challenging job. I’ve been working on the Underground for 15 years and the way this [project] office

“the biggest thing is that it is a complicated, logistically challenging job” Jez Haskins, TWBN

Central lined: Secondary lining installation is underway

NEW LOOK: TOTTENHAM COURT ROAD

New high capacity entrances

Expanded Tube ticket hall

New Central Line access

Existing Central Line

Existing station infrastructure

Existing Northern Line

New Northern Line access

New Crossrail infrastructure

Ticket hallbox under

construction

Central Linecongestion

relief tunnelssecondary lining

being installed

FutureCrossrail 2access

Central Lineplatform bridgesto be built

Goslett YardCrossrail station box

under construction

New Northernline access tunnelunder construction

New Northernline access escalatorbox complete

Oxford Street

Centre PointTower

SITE

New Oxford Street

Charing Cross Rd

Tottenham Ct Rd

High Holborn

0 40m

New high capacity entrances

People mover: TWBN excavated a 30m deep box for new Northern Line escalators

16 NEW CIVIL ENGINEER 01.03.12 | www.nce.co.uk

COVER StORy: TOTTENHAM COURT ROAD UNDERGROUND

is set up, we really do resolve problems.” Everyone is co-locat-ed, and working as one team.

“It is also a significant achievement to have reached 1.5M man hours at Christmas without a lost time reportable accident,” states Hamilton.

“The safety statistics speak for themselves,” adds LUL senior section manager Steve Lousley. The impact on the community in terms of noise and disruption has also been minimal. “We have had a remarkably low number of complaints,” says Haskins. This was, and continues to be, vital to remaining on programme.

“It would be so easy to lose night working,” explains Lou-sley. “It can be as simple as an honest mistake. It is testament to the way the contractor has instilled the right behaviours into the workforce.”

But the job is far, far from being done.

On the Northern Line, with the reshaping of the platform complete, TWBN is focused on building the new access routes for passengers.

Excavation for the Northern line escalator box – along with the project’s unique D-shaped pile – is complete, and its con-

crete box lining is being built inside. At the same time, excava-tion of a passenger concourse tunnel from the base of this box deep below Charing Cross Road began this week, with TWBN using the sequential excavation method, a technique more com-monly referred to as the side wall drift method.

It is a derivation of the observational method and sees the tunnel excavated in four segments, with the inherent strength of the ground used to support the work during excava-tion. It requires a delicate touch.

“The devil is in the detail,” says TBWN project manager Mike Curran. “That and getting the waterproofing right.”

Back above ground and gazing down from Centre Point tower’s viewing gallery, it is clear that there is much still to complete. Not least for the expanded ticket hall, which is being built using techniques traditional in big basement construction.

Four dimensional modelling was used to calculate the prop-ping needed to support the walls of the ticket hall’s box and its 840 bored piles while excavation and concreting can take place. “We are currently excavating as well as propping,” says Haskins. The first base pour was sched-uled for last Friday. “We are pouring 2,000m2 in total – that’s 22,000m3 of concrete and 4,000t of rebar.” The plan is to complete the concreting this year.

Back underground and further east, work to install the second-ary lining for the new Central Line access tunnel is well underway. This is a cast insitu reinforced concrete lining and features 32mm diameter rein-forcement at 150mm centres.

The 115m tunnel was driven alongside the Central Line last year. It has advanced in a con-trolled sequence using an exca-vator bought specifically for this task and for use on the Victoria

Underground Station upgrade project – also being carried out by this JV.

A design change instigated by the contractor is boosting safety here – the sprayed concrete pri-mary lining is fibre reinforced. “Replacing all steel arch mesh with fibres means we haven’t got to put men under any exposed face,” explains TBWN site agent Dave Harper. The 350mm layer of sprayed concrete was then ap-plied by a robot.

The tunnel is unusual for two reasons. Firstly, it expands from 4.5m diameter to 5.5m diameter as it heads west. Secondly, it is the first piece of work for the proposed Crossrail 2 scheme from Hackney to Chelsea in the form of the beginnings of the cross-passages that would access its platforms.

“These are the first two bits of work in London for Crossrail 2,” says Harper, gazing at the side passage stubs and their concrete lining. “In 25 years time I might get to work on the other side of this lining.”

Once the secondary lining is in place, the project team has four track possessions in May and June to excavate out two ac-cess passageways above the

“It is also a significant achievement to have reached 1.5M man hours at Christmas without a lost time reportable accident” Les Hamilton, LUL

PLAN VIEW: LATEST BIRD’S-EYE VIEW OF THE COMPLEX SITE

CROSSRAILGOSLETT YARD

FALCONBERGBASEMENT

FALCONBERGSHAFT

OXFORD STREETENTRANCE

TICKET HALLEXISTING

TICKET HALL

NORTHERN LINEESCALATOR BOX

CROSSRAILGOSLETT YARD

FALCONBERGBASEMENT

FALCONBERGSHAFT

OXFORD STREETENTRANCE

TICKET HALLEXISTING

TICKET HALL

NORTHERN LINEESCALATOR BOX

18 NEW CIVIL ENGINEER 01.03.12 | www.nce.co.uk

COVER StORy: TOTTENHAM COURT ROAD UNDERGROUND

The job of getting the piles for whole station upgrade in is a story in its own right (NCE 25 August 2011).

A Bauer/Keller JV was awarded the contract in 2009 with the work beginning in anger in March 2010 when most of the project team arrived on site. Work was divvied up, with Bauer carrying out rotary piling.

The construction phase began in April 2010, with the installation of the first rotary pile on the Northern Line escalator box’s secant pile wall. The main load bearing primary piles were constructed using 1,180mm segmental casings. Smaller secondary piles consisted of 600mm CFA piles. In total, 90 linear metres of secant wall were successfully constructed on time and to budget.

Without question the biggest challenge were the three large diameter rotary piles that had to be installed into the western side of the escalator box’s wall.

All rotary piles were complex, with diameters up to 2.43m and depths up to 64m. Four were constructed using a slip coated liner with bitumen coating to a depth of about 30m below ground level to eliminate the load transfer between the new escalator box and these piles.

But the remaining three piles were something else, demanding even greater care as they were so close to the Northern Line running tunnels.

These piles had to be permanently cased to well past the axis of the tunnels, to 35m depth. They also contained bitumen coated liners. Bauer’s BG40 rig – the most powerful in the worldwide market – was used to construct them.

The drilling tool only just fitted over the permanent casing, with barely 50mm to spare. An oscillator was used to assist with the installation of the permanent casing. Casings had to be pushed into the ground 1m at a time and then drilled – again just 1m at a time.

One of these three piles is truly unique – the “D” pile. So named because the top half of the pile is D-shaped, with the flat section of the pile aligned parallel to the box structure. It was the only way to fit the pile between the box and running tunnel, so tight were the tolerances.

A Truly ChAllENgiNg piliNg job

Central Line running tun-nels. These will eventually allow passengers to and from the new access tunnel to the platforms.

But even this is complicated by a lack of headroom as a sewer runs very close to the tunnel crown. As a result, the platform tunnels must have their roofs flattened by taking out curved cast iron rings and replacing them with flat steel ones. Once they have been removed steel bridge decks will be slid into position, replicating existing crossing points further along the platform.

Back above ground the final piece of the jigsaw – the huge four storey box that will form the Crossrail ticket hall beneath Goslett Yard – is also starting to take shape. Perhaps surprisingly, a great deal of Crossrail con-

struction is being done as part of this contract.

It is surprising because construction of the Crossrail station at Tottenham Court Road is, strictly speaking, two separate contracts. First, the Bam Nuttall/Ferrovial/Kier joint venture is creating the sprayed concrete lining platform tun-nels and access shafts as part of its £400M to £550M Western Running Tunnels contract that

will also take in Bond Street. Then the station proper will be built under a £100M to £250M contract, currently out to tender. But there will be relatively little to do, as the station box for the eastern ticket hall is being built by TWBN as part of the Tube station contract.

It will be the first station box to be built on Crossrail’s central section.

Bauer was contracted to build its 44m deep diaphragm wall box and 11 plunge columns that will enable the top down construc-tion of the box.

Work on the diaphragm wall began in November 2010 and was completed in May last year. Work on the plunge columns then ran from June to July.

The 1m thick diaphragm wall was generally built in single

bite panels 3.2m long to reduce ground movements in the sur-rounding area. To say the walls are beefy is an understatement. The reinforcement cages consist-ed mainly of 50mm bars, which are closely spaced as is possible without restricting concrete flow. The massive reinforce-ment cages had to be connected on site using a combination of splices and couplers to build the entire 44m length.

The plunge columns, installed into large diameter 48.5m deep piles, are not small either. The 600mm x 600mm and 700mm x 700mm columns up to 33m long are by far the heaviest and longest the industry has seen for quite some time.

“Last year we built the diaphragm wall,” notes Curran. “Now we are just starting to dig.”

Help point: The 115m-long access tunnel was driven alongside the Central Line

“the devil is in the detail. that and getting the waterproofing right” Mike Curran, TBWN

tough: Huge plunge columns