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Eight cranes, three teams, one site: Vinci tackles King's Cross conundrums

Vinci, Bam Construct and Kier are rubbing shoulders on a site that also has plans for six high-rise blocks and a new public square.

Project: BNP Paribas new UK development business
Client: BNP Paribas
Contract value: £80m
Region: London
Main contractor: Vinci
Piling subcontractor: Bachy Soletanche
M&E subcontractor: Shepherd Engineering Services
Steelwork subcontractor: Severfield
Cladding and glazing subcontractor: Focchi

For many years the post-industrial backwater around King’s Cross seemed to be in terminal decline.

Since the Second World War, the decline of rail freight transformed the area from a thriving distribution district to a scrimmage of underused and largely derelict space, dogged by crime.

But when work began on High Speed One in 2000, the area’s prospects began to change. When the London Terminus of the Eurostar moved to St Pancras station in 2007 redevelopment began in earnest.

Now, the scene is barely recognisable.

The former site of iconic but derelict gasholders is now a canyon of tower cranes and scaffolding looming over a smart pedestrian walkway running between the future site of Google’s new HQ and a clutch of high-rise office developments.

One of the largest projects in Europe

A thriving mixed-use district is taking shape between the station concourse and the University of the Arts, in one of the largest construction projects in Europe – so big in fact that it will be designated its own postcode, NC1. The scheme is worth £2bn and covers 27 ha, including 3.4m sq ft of office space and 2,000 homes.

Developer Argent has now assembled a glittering line-up of tenants including Google, BNP Paribas and Camden Council, although a deal with Sainsbury’s, which Argent is in the process of renegotiating with a new partner, fell through.

Outline planning has been granted for the whole site, with detailed planning applications made on a rolling basis.

The northern side, known as Zone B, is the current epicentre of activity, with Vinci, Bam Construct and Kier all on site in close proximity at the same time, with eventual plans for six high-rise blocks and a new public square.

“The deliveries are all to do with making sure we demonstrate what’s on the server, when it’s coming and how much of it is coming in”

Philip Willmott, Vinci

Bam is building two office blocks while Kier is working on a £70m office for Camden Council, including a leisure centre.

Running along the northern edge of Zone B is Vinci’s patch, where the firm is building an 11-storey office for Paris-based banking group BNP Paribas, in the largest project in the zone and the last to be signed off.

Two other office schemes, B5 and B6, are planned for the zone, with B5 currently acting as Bam’s site compound.

Vinci fended off Kier – one of the dominant firms in King’s Cross Central – and Skanska to win the £80m project, which will see an open plan office erected with 328,000 sq ft of commercial space and 10,000 sq ft of retail on the upper ground level, complete with terraces and a green roof.

It is the BNP’s first building in the UK and will eventually house all its London staff, who will take about 55 per cent of the building, consolidating from various sites in the West End, Marylebone, Chancery Lane and the City.

Slipform cores arise

The basement slab and mezzanine deck are complete, with twin slipform cores – one complete and one in progress – rising out of the site at 300 mm an hour.

The project has a distinctly continental flavour, with the client, main contractor and lead architect Jean-Michel Wilmotte all hailing from across the Channel.

But working in such close quarters with other contractors in a highly congested area brings unique challenges. In Zone B alone, for example, Bam fields four tower cranes, Vinci two and Kier two more, resulting in a major safety and logistical challenge.

The different contractors’ drivers are all in constant radio connection, with banksmen and slingers on the ground communicating with their cranes and each other.

Each of the three firms also employs a crane co-ordinator, who all meet weekly and make sure the correct lifts are loaded up at the correct time, with a site manager overseeing the entire project.

Additionally, SMIE anti-collision systems automatically shut down the cranes if they come too close together – a safeguard that has not yet been needed on the site.

Monthly contractor meetings are also held to co-ordinate crane movements and other site activity between Bam, Kier, Vinci and Argent, with delivery schedules another central topic.

At the time of Construction News’ visit the project was running about a week behind schedule, but the firm was confident steelwork could begin on the “key day” of 5 August, to be carried out by Severfield Rowen.

One area where the close proximity of the scheme is a boon was in excavation work, which Argent has excavated and remediated before Vinci began.

The site previously held the area’s notorious gas holders, and stood at road level before Bam Nuttall carried out excavation works for Argent.

Planning to avoid further delays

A mixture of steel reinforcement bars up to T50 are also to be used on the main building, with all steel beams coming with holes in so services can be run through without interfering with the raised ceiling.

“The amount of internal area is a key for a client – they don’t get paid as much if there’s less internal area”

Philip Willmott, Vinci

This, according to Vinci major projects director Philip Willmott, could be a big hold-up for the programme if the holes for the services were in the wrong places in the steel, which is shipped in from a prefab Severfield plant in Yorkshire.

To address this, Vinci is checking through floor designs on a monthly basis to ensure cladding and steelwork are in sync and to maximise floorspace.

“The amount of internal area is a key for a client – they don’t get paid as much if there’s less internal area,” Mr Willmott says.

The building was designed according to Paribas’ specifications and handed over to the contractor for detailed design at stage D.

Part of this design inheritance is the concrete specifications, which will be C40 for general floors, C50 for the slipform, and C60 for columns and walls.

Building information modelling is also being used for co-ordination, with architects, concrete steelworkers and services all sharing a model, with review meetings to ensure all parties are working together.

Environmental factors affect schedule

Contractors currently provide Argent with environmental data, wastage and energy usage to allow for better co-ordination and monitoring.

Though weather has not presented a major problem on site, around 80 hours or so per month were being lost because of wind disabling the tower cranes.

Having to stick to a strict timetable or risk clogging up the area’s infrastructure has meant working on the slipform until 9.30pm through a special agreement with the local authority.

Up to 30 people work in the core at any given time, and an accelerator is used in the concrete to ensure quicker hardening.

Camden Council has also struck an agreement with Vinci that sees 15 per cent of the workforce locally employed, with 5 per cent being apprentices.

Substructure work, being carried out by Masterton Holdings, began in February, taking around four months, with Focchi’s cladding work set to begin in October this year.

M&E and public health finishes will then begin under Shepherd Engineering Services next August.

Foundations on a former gas storage site

Bachy Soletanche, on behalf of Bam, installed 300 CFA piles of 900 mm and 1,050 mm in diameter to a depth of up to 30 m with two piling rigs, then it took the ground 8 m lower than the top of the pile to achieve free cantilevered mode.

The ground – entirely London Clay – was well suited to foundation installation and the work was finished a week before schedule.

However, the gas holders posed unique obstacles, with a different design needing to be used to accommodate submerged brickwork from one of the old structures.

Another section of the piling wall – installed by Simplex-Westpile – had to be supported by three rows of 15 m pre-tensioned and pre-grouted ground anchors and waling beams to accommodate the base of one of the gas holders.

Around 80,000 cu m of material had to be removed, most of it contaminated by the holders.

During this process the secant pile wall on the perimeter had to be fastidiously monitored, as it was expected to deflect by up to 30 mm during the excavation. Plowman Craven performed this work with a network of 60 3D prisms mounted on the pile wall to aid measurement.

Other risks include health and safety, with 150 people on site at any given time, though the only major incident had been a lost end of a finger.

Vinci uses Alsipercha fall arrest rigs to mitigate the danger of working near edges on the site.

 

Main contractors co-ordinate

Vinci major projects director Philip Willmott describes co-ordinating deliveries through congested central London as “the biggest challenge”.

Vinci is operating a web-based tracking delivery system, which requires all deliveries to be logged 48 hours beforehand.

As Vinci and Bam have been sharing an entrance at various phases, the two contractors have had to log their deliveries into each other’s systems – though Kier uses its own entrance.

A detailed traffic management plan is also in place, with Cemex-supplied concrete wagons reaching the site from their plant north of the development.

“It’s all to do with making sure we demonstrate what’s on the server, when it’s coming and how much of it is coming in,” Mr Willmott explains.

“My team has to completely understand how the whole operation works.”

The Vinci team prefers using a separate concrete supplier to the other contractors to avoid confusion and overtrading.

“Either a mistake could happen and we could get the wrong concrete, or they might not be able to supply because they’ve been booked in, for example by Kier,” Mr Willmott says.

The scale of this challenge is only going to increase as more phases of work come on stream – not to mention when work begins on Google’s HQ in early 2014, with most of Vinci’s traffic coming off the main road by April.

That project will make up Zone A. At present the contractor’s meetings only encompass Zone B, and there is not much communication between other zones.

The build is set to ramp up internally as well – Vinci’s site office wall is emblazoned with a progressional wall chart showing the phases of the build when different contractors will be on site, with the layers multiplying from late 2013 as the cladding and fit-out begin in earnest.

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