Look across the River Thames from Rotherhithe and you will see, emerging from the cluster of high-rises that make up Canary Wharf, the Landmark Pinnacle Tower, the area’s latest mega-project – and it will be filled with high-end apartments.
Project: Landmark Pinnacle
Client: Chalegrove Properties
Principal contractor: Chalegrove Properties / J Reddington
Architect: Squire & Partners
Structural engineer: WSP
Subcontractors: Miller Piling, Trent Precast, KFK Facades
Start date: March 2016
Completion date: September 2020
Situated on the western edge of the capital’s business district, the Landmark Pinnacle, when completed, will stand at 239 m and become Canary Wharf’s second-tallest building.
“It will be just one metre shorter than One Canada Square when it is finished,” says Alex Bui, associate director at WSP, the project’s structural engineer.
But unlike One Canada Square, which includes offices for businesses and organisations such as HS2 and Barclays Bank, the Landmark Pinnacle will be filled with high-end apartments.
And being a residential block calls for an emphasis on maximising floor space, meaning it will have 75 storeys when completed, compared to the 50 floors that make up its fractionally taller neighbour.
Another difference to One Canada Square, which was built in the early 90s when Canary Wharf was far less developed than it is today, is that the Landmark Pinnacle project team has faced more spatial challenges.
“This is 100 per cent the tightest site I have ever worked on,” says J Reddington project manager for the build, Sam Patton.
Maximising floor space
Structural engineer WSP is no stranger to designing tall buildings, particularly in Canary Wharf.
The firm was also the engineer for Canary Wharf’s 58-storey Newfoundland tower – a mere three-minute walk away.
But the sheer height of Landmark Pinnacle has brought new design challenges. The stability system is comprised of a central core, which engages two perimeter columns.
This is further supported through a series of outrigger walls that will be positioned at different locations across the building’s 75 floors.
“That is the enhancement we require to provide the sufficient stiffness to the lateral system of the tower to make sure its stands 239 m tall,” Mr Bui says. “To just rely on the central core is not sufficient for a building of this size.”
Landmark Pinnacle J Reddington Chalegrove Properties 3
And with the tower being a residential apartment, WSP’s design has also had to ensure the building has as much sellable floor space as possible.
To get all the floors in, extra space has had to be found in every part of the design..
“In these sort of high-rise buildings, the client will always want to squeeze the floor slabs as much as possible,” Mr Bui says. “Even losing 25 mm over 75 storeys is a lot of height, that is why you want to get them as slim as you can.”
Mr Bui says those [floor slabs] being used have a thickness of just 200 mm – about the thinnest you can use for a building of this type.
“This is about as slim as you can get. Anything slimmer than that and you will start getting rebar and acoustic issues,” he adds.
The building has required economical MEP, too. In most high-rise projects the concrete structure is completed first and the MEP added later.
But with a brief to maximise space, WSP’s design has incorporated the MEP into the structural elements where possible.
“Often, by the time you add the MEP distribution, you are taking out a lot of head height,” Mr Bui says. “What we have come up with is to integrate the structure and MEP together to squeeze those two zones and give back the ceiling height.”
When J Reddington started enabling works, it soon realised just how tight the site was.
“When we started digging out to start with we had only about a metre to the hoarding line and that is bearing in mind we are digging 14 m deep,” Mr Patton says.
The Landmark Pinnacle is nestled between two other towers also built by Chalegrove Properties.
“At the start we had two giant piling rigs. It’s very unusual to have such big ones so close in this tight space,” Mr Patton explains.
On the other side of the site is the River Thames. To protect works, operatives installed a secant piled wall around the site on three sides.
Proximity of piping
The project team also had to be aware of a listed pumping station situated nearby.
This, which is still in operation, pumps water from the Thames every 24 hours and is supported by a network of pipes just metres away from the Pinnacle site.
Mr Patton says the piping was a constant worry when piling. “There was literally a metre clearance between the site and the pump and its pipes,” he says.
“We had to be very careful when we were doing the piling work because there was the potential to interfere with the piping and drainage.”
“At the start we had two giant piling rigs. It’s very unusual to have such big ones so close in this tight space… You will probably find only five tower cranes have been up this high, ever, in London”
Sam Patton, J Reddington
He says this required some precision work from subcontractor Miller Piling, as well as monitoring of ground movement.
To do this, probes were put down with the piles four times a day to check for this and ensure it didn’t impact on the pipes.
In total, 220 bearing piles were drilled down to a depth of 18 m under the tower. A further 137 soft and 138 hard piles were drilled as part of the secant wall.
But drilling did not come without its own issues.
The stratum for the Canary Wharf site comprises Thanet Sand, an extremely hard ground condition. While this provides a great foundation for high-rises when the piles have been drilled, it does create problems for rig crews.
“When you hit the Thanet Sand its like granite stone – we lost a couple of augers in the process,” Mr Patton says.
A structure of the Landmark Pinnacle’s dimensions has required a super-strength material.
From the basement to the 22nd storey, the core and outer columns needed C85 concrete – some of the strongest being used in the country.
“You might see it in Asia, but you don’t see it used very often on buildings in the UK,” Mr Bui says.
And for J Reddington, it did provide some challenges, which led to the firm seeking advice from Tarmac about how to manage it, particularly when using it to slipform the tower’s core.
What quickly became apparent was the speed with which it cures.
“It is very difficult to work with this concrete – it goes off very quickly and the consistency is different because it is so strong,” Mr Patton says. “It has caused us a few problems during construction.”
It was a daily race against time for the team, which was armed with two high-powered jet washes to clean away the concrete so it did not close the shutters used during the slipform work.
“We have managed it alright, but it has been difficult,” Mr Patton admits.
Landmark Pinnacle J Reddington Chalegrove Properties 7
Another key to the success of the scheme is the phasing of the work.
“One of the biggest challenges on this job is co-ordinating the height of the slipform with the floor slabs and then with the tower crane,” Mr Patton explains.
“You have to climb the tower crane when the core and floor slabs catch up.”
The process J Reddington has adopted sees the core slipformed up 3 m, the equivalent of one floor height. The floor slabs are then installed around the core. Once this happens across four floors, the crane is bolted to the building.
When it has been secured, it can then be built higher before the process starts again.
The J Reddington team has developed a system where each floor can be delivered in five days.
“It is a process that has to be very finely tuned and timed well so everything carries on and construction doesn’t stop,” Mr Patton says.
With the facade on the side of the building now being installed, it is important the concrete structure stays ahead of the facade contractor.
Part of this quick turnaround of floors has been driven by the use of precast columns.
Mr Patton says the slabs that arrive from Trent Precast’s factory in Nottinghamshire have accelerated the speed of the build massively. If the precast columns arrive at the site at 8am, by 11am, the team will be able to install five or six columns.
“If you install five columns, normally it could take a couple of days; doing them precast could take a matter of hours,” he says.
With another 22 floors to be built, there is still a lot to do before it completes in 2020. And the sheer size of the building, and more specifically its crane, means the project team has had to think about the airspace around the tower.
“You will probably find only five tower cranes have been up this high, ever, in London,” Mr Patton says.
Just four miles away from City Airport, one of the team’s tasks was to get permission from the Civil Aviation Authority (CAA) to build the crane. “We have had awful problems getting their heights passed through the CAA,” he notes.
“The biggest challenge I can see is logistics. We are going to have the dryliners coming in every day in such a small area, which will be a challenge”
Sam Card, Chalegrove Properties
As part of the agreement, the team has had to get a custom-made part for the crane, much shorter than the 6 m components that make up the rest of it.
“We’ve had to get a specially made part,” says Chalegrove Properties façade manager Sam Card. “It’s all been approved now, and that is with the custom-made section.”
And as the crane continues to grow, so will the number of people on site. Currently there are 120 workers, but at peak construction, that number will rise to 500.
Mr Card says that with the extra people and supplies coming to the site, organising the people and deliveries in such a tight space will become the biggest difficulty (see box, below).
“The biggest challenge I can see is logistics,” he says. “We are going to have the dryliners coming in every day in such a small area, which will be a challenge.
“But so far everything has gone really well – we are delivering a floor a week.”
Military precision required
Any project of this scale, delivered in such a built-up area, comes with its fair share of challenges.
On Landmark Pinnacle, these have been greater than most.
“Logistically it is very tight,” Mr Card says. “We have had to work very hard to ensure everything gets delivered on time.”
With such a restriction on space, nothing can be stored locally, meaning it is important to keep the deliveries moving through the site.
And strict council guidelines on when traffic can arrive makes organising the deliveries an almost military operation.
This precision was demonstrated during the muck-out of the basement, when the site team had to co-ordinate a turnaround of 170 wagons every day.
“We set up a through road from Westferry to Marsh Wall, with 170 wagons almost like a train, during the dig,” Mr Patton says.
And all of this had to happen throughout the day due to the council limits on work.
“We are just out of the boundary of Canary Wharf Contractors’ area, whose team pretty much have immunity to work through the night, but we are have been set from eight until six by the council,” he adds.