A tale of two bridges
London’s traffic is legendary. Take the A40. Running west through the center of the English capital, the roadway handles more than 100,000 vehicles a day. It also traverses some of the city’s busiest rail networks. But two of the A40 bridges dating back to the 1920s were in serious disrepair and in dire need of attention.
Transport for London, the government body responsible for most aspects of the city’s transport system, realized the bridges had to be replaced. It just had to figure out how to pull off the project—without disrupting all that traffic or the neighbors.
Hyder Consulting, which won the bid for the approximately four-year, £16 million project, knew it was in for some serious logistical snarls.
“One of the biggest challenges was the railway,” says Phil Tindall, the London-based U.K. technical director for bridges at Hyder.
Together the rail lines handle more than 800 trains, transporting 145,000 passengers daily.
The first bridge, which goes over the North London Line, has trains running 18 hours a day.
That one didn’t seem overly daunting.
“Without too much difficulty, you can get five to six hours on the nights or the weekends to work over the railway lines,” says Mr. Tindall, who started out as project manager for the job and was later promoted to project director. “You could get an extended blockade of the railway line and close it for a whole weekend if you had to.”
970 tonnes The weight of the steel girders used in constructing the bridges— the weight of 130 London buses
But the second bridge was another matter altogether.
Crossing the main rail lines that come out of Paddington Station— including the Heathrow Express, serving the city’s busy airport—the bridge is in use almost 24/7. At the project’s inception in October of 2005, the bridge was functioning 21 hours a day, 363 days a year. Now it runs every day.
“Doing everything over such a busy railway line involves working in possession periods of three hours or negotiating with the owners of Heathrow Express to close the line for a period,” says Mr. Tindall. “They wouldn’t agree to it very easily or without payment of a very large sum of money to enable them to put people on buses with advance publicity and recoup loss of profits.”
Under more forgiving circumstances, the bridges would have simply been torn down and replaced.
“The conventional wisdom for something like this is you take a 48-hour railroad possession, you build something offline, demolish the old bridge and get it there in one go,” he says. “But that was looking like it was going to cost far too much money and be far too difficult.”
Two other factors foiled the drop-in approach: a lack of nearby land where new bridges could be built and the extraordinary amount of utility equipment running through the decades-old structures.
“There are gas mains, electricity mains—11,000 volts, fairly high-voltage electric—and masses and masses of fiber optic cables that are feeding places including the BBC‘s main studios,” Mr. Tindall says. “So you’ve got to find somewhere to put all that utility equipment first, which would mean a double diversion of utility equipment. You’d have to put it onto a temporary bridge while you put the new bridge in, then transfer the equipment to the new bridge. That was going to cost an absolute fortune.”
As if dealing with all the infrastructure logistics wasn’t enough, Hyder Consulting also was up against an array of powerful stakeholders. To secure buy-in from the very beginning, the company relied on in-depth workshops with key stakeholders, largely highway operating and rail authorities.
“The workshops are done around a value-management exercise so that we’re exploring alternative ways of doing things,” says Phil Tindall, Hyder Consulting.
“Rather than everything being a fait accompli, we can involve the stakeholders in some of the decision-making,” Mr. Tindall says. “Even though the basic methodology is already there in outline, it’s still important to allow for modification or change if something happens in the workshop.”
Before starting the workshops, Hyder Consulting discussed its objectives with a professional facilitator, who helped pull in the right people from each of the major organizations.
“We want to make sure we have people who are senior enough that they can make decisions,” Mr. Tindall says. “We want to make sure they don’t have to go back to their organizations and be overruled.”
The facilitator then touches base with stakeholders to cover main points in the agenda and seeds thoughts about the issues they might want to discuss.
“The quality of the facilitator and the amount of pre-work he or she does is as important as what happens on the day of the workshop,” Mr. Tindall says. “If you don’t have that stuff ahead of time, what happens at the workshop is not as effective.”
Clearly, conventional wisdom wouldn’t apply for this project.
OUT OF SEQUENCE
Confronted with a host of options it couldn’t use, the team faced the roadblock with a simple premise: What can we do?
One option was to use the available space to build a couple of lanes’ worth of traffic alongside the existing bridges, Mr. Tindall says.
“Using that as a principle, we worked out a sequence in which we could move the utilities and move the traffic around through all the different phases,” he says.
The team eventually arrived at a solution by giving sequence the same weight as design.
“There are so many jobs where the consultant will do the design or the permanent works, and the contractor has to figure out what the construction sequence is. ‘How am I going to build it?’” Mr. Tindall says. “For this project, everything was worked around the sequence.”
Breaking with convention, the team completed the demolition and construction in multiple longitudinal slices along each bridge.
“That was something that was new to us,” Mr. Tindall says. “Working in London—replacing bridges over railway lines and dealing with all these utilities— we’d done that quite a bit before. Our advantage was experience and doing things in more conventional ways—and knowing ahead of time what works and doesn’t work, and where the risks lie and what you can do to mitigate those risks. But the particular constraints of this bridge drove the construction methodology and sequencing.”
vehicles that use
the A40 per day
How did I handle the stakeholders? “Patiently” is the word. You do a lot of talking, and very early on in the project, we held a series of value-management workshops that involved some of the key stakeholders— the highway operating and rail authorities, the real major players.
As with many projects, the devil was in the details.
The team had to look at every aspect of the construction in light of the piecemeal nature of the project. All of the steel beams were sized and arranged to suit the amount of space available and the variances demanded by the planned sequence of sectional replacement.
The reinforcement of the bridges’ concrete decks was also designed to suit the construction sequence. Steel formwork was used on top of the steel beams so the bridge decks could be layered in concrete while trains ran underneath.
“With a lot of steel formwork systems, you get gaps that are less than a quarter of an inch [one-sixth of a centimeter] wide. So when you form the concrete, you’ll get water and cement paste dripping through there,” Mr. Tindall says. “Because the railway lines are underneath and it’s high-voltage electrical, you can’t afford to have wet concrete dripping onto those overhead lines because there’s a possibility of electrical shorting. Also, the cement paste goes onto the wires, so when the connector of the train comes along, it hits the cement paste and wears things very badly.”
In many ways, working around the A40‘s constant flow of cars and trains was a matter of simple traffic direction. The larger issue was dealing with the project’s panoply of powerful stakeholders, including the transport authorities as well as the British public.
“How did I handle the stakeholders?” Mr. Tindall asks. “‘Patiently’ is the word. You do a lot of talking, and very early on in the project, we held a series of value-management workshops that involved some of the key stakeholders— the highway operating and rail authorities, the real major players.”
Hyder used the meetings to present its concept and then listened to the stakeholders’ issues and discussed ideas and solutions.
“We got everybody to work together to buy into it, and that was very important in terms of getting a way forward,” Mr. Tindall says. “Then, for the other parties who weren’t quite so crucial, we did a lot of liaisons, a lot of talking and a lot of meetings. You’d agree on things, and they’d go away and come back with something else. We went through a whole series of iterations to get there in the end.”
“The result of the feedback was factored into the proposals where possible to ensure that the design met the needs of the customers,” says Chad Frankish, portfolio manager at Transport for London and project manager on the A40 project for its last two years.
The project team decided to review the pedestrian crossing proposals, for example, after receiving the community’s feedback.
To keep locals in the loop, the team made visits to neighborhood schools, sent out a quarterly newsletter and set up a telephone helpline.
The team also tried to minimize the impact on commuters as well as the neighborhood and its residents, doing as much work as possible during the daytime when cars and trains were on the move. But for safety reasons, some tasks—such as the swap-out of concrete sections—were performed during the three-hour increments when the trains weren’t running.
Pedestrian and cyclist access was also maintained throughout the project.
Looking to keep a low carbon footprint, the team set a target of achieving a 5 percent reduction in CO2 emissions and waste sent to landfills, and developed an extensive landscaping plan for the area around the bridges.
The efforts earned the team a silver 2009 national award from the Considerate Constructors Scheme (CCS), a British organization set up by the construction industry to recognize best practices beyond statutory requirements.
“Transport for London requires all of its contractors to sign up to and abide by the CCS code of conduct,” says Mr. Frankish. “On the A40 project in particular, strict adherence to the CCS resulted in minimal complaints and those received are actioned immediately. By good teamwork, a proactive public relations strategy and a united project management approach, the project management team has been able to exceed the required standards.”
END OF THE LINE
With the exception of some finishing and landscape work, the team is on track to wrap up work this month.
Over the project’s four years, the team suffered no major accidents and even managed to integrate some upgrades, such as creating access and crossing improvements for pedestrians, cyclists and people with disabilities.
And that legendary London traffic is moving smoothly—above and below the bridges. PM
Number of passengers on the 800 trains that travel underneath the A40 bridges every day
PM NETWORK SEPTEMBER 2009 WWW.PMI.ORG
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